996 3.6L street engine race car owners. Where do you shift?
 

If you have a street powered 996 3.6L engine, where do you think its best to be shifted at, for maximum acceleration down a straight at a track near you.

as we all know, the gear spacing for 3-4th is an RPM that ends up 80% post shift RPM, and from 4-5th, 85% of that pre shifted RPM.

There is some thought, and even some lap time data that shows that the 996 engine, makes just a bunch of "noise" up top and its better to short shift by 300rpm. what do you think?? HP is generally flat up top, as torque flat and is falling as soon as 6000rpm.

There is a guy named Newton that would disagree with this technique, given that the 996 hp curve is fairly flat up top and produces more HP to redline than post shift, even in 4-5th and especially 3-4th

What do you think and do at the track?

Mark,

Another example of how not to endear yourself to the masses....

Scott

If anybody actually cares PM/email me an actual dynojet file and gear ratios and I'll figure it out.

I'll give a little crumb to Kibort here, do I want to calculate wheel trq or hp? :icon107:

Greg,

Based on the article I posted in that other "Kiborted" thread, you want to "shift to maximize transmission output torque".

Here is the article link again:

http://www.allpar.com/eek/hp-vs-torque.html

Scott

I know the answer, I figured I'd just get Kibort all worked up on HP vs torque.

You know that wheel torque (after the transmission) and HP tell the same story at ANY vehicle speed. :) So, either one will work. I have no preference.
HP is just easier to work with. less to calculate to find performance maximization. maximize HP, you maximize rear wheel torque! :cheers:

There really is nothing to figure out. just get the gear shift spacing and plot it on the HP curve. if the post shift RPM hp is the same, then you shift generally.

Which is the same as maximizing HP at any vehicle speed, by definition.

I think the masses appreciate someone that questions authority and helps to find solutions. IF I help one interested sole in figuring out that the "noise" up top in RPM is utter BS in most cases, it is all worth the critism. Im obviously not here for a popularity contest or I wouldnt be agreeing with butt dyno boy, VR and his posey. Im only here to show what is true and correct, and learn something myself.

Mark,

It's not the questioning that is offensive.....as I have said before, it is pointless trying to discuss anything with you.

Scott

Please make it stop.....

Its kind of funny with you. you get it, obviously with the article you posted, yet you have an issue "discussing" it? I dont understand. what is hard to discuss, is a topic when facts are brought up and some just says your wrong.
If you dont want to discuss, you should just get a blog.

some of these guys take this stuff WAY to seriously. news flash, this is a forum, discusson board. Like guys at the track just talking, but its in priint.
nothing more, nothing less. BUT, its a great way to research, share information, and also have a little fun doing so.

anyway, the results are in. as I thought, there are some blind sheep. :)

Good luck with that...

on my m96 fall goes after 6900 rpm. there is definitely no fall at 6K, it pulls pretty equally to 7200 or so, redline is increased to 7500 but i try to upshift at 7.
http://www.6speedonline.com/forums/p...pictureid=8782

i run it 5k-7k usually on a track, if it goes close to 4500 it feels pretty stall.

One final comment to you:

It's funny with me??? You are too much! The problem you have is not whether you are right or wrong. It's how you present your opinions, right or wrong. You have the subtlety of a tornado in a trailer park.

Scott

Moderators,

Is there an "ignore poster" feature we can get enabled?

Scott

really??? really? are you really that much of a princes.

"Daaaaad, tell jonny to stop pushing me".


Scott, here is a hint. you dont want to discuss, dont read the posts.

The way to find the answer, which I think Greg is offering to do, is to calculate wheel torque in each gear across the powerband. Then you look at where the lines cross for each successive gear. If the thrust force of the next higher gear is lower than the thrust force in the preceeding gear, you keep accelerating all the way up to redline. I've never run the numbers on the 996, but given that the gearbox is geared for the street and has what we would consider relatively high gaps, I am going to guess that fastest acceleration in 3rd and 4th gear will always be achieved by running the engine up to the limiter before shifting.

the way I present?? Really?

hmm, why dont you do both of us a favor. read the last thread and my post regarding the comments made about the topic. see what I said, and then see what the reponse back from who ever. I re read it and I think it was very informative, especailly if I am right. you often hear of folks short shifting intuitively, as VR has suggested, even if it is by 300rpm. Most of us *(are racers) and want the most out of our cars, so why would this be a good idea, even though their data (which we have never seen ) supports their point?
What I presented is hard core fact and it can barely be argued to the contrary if we are talking straight line acceleration. thats like saying, if you take a longer time to shift, your drag times will be better. Its just not true!
Their data is swayed by many other factors, as we all know, existing during a lap.

if you can handle the power, shift at a point that maximizes HP for your engine.

Yes, and this is the point of all this. But, what greg is offering is totally unessesary, unless you dont understand the concepts of power.

in the end, the power curve dictates your ability to accelerate, (as does the curves or plots Greg is offering) they will be identical. shift at a point where equal power is found after the shift and you maximize area under the HP curve.

shift earlier, and you are leaving sometimes BIG HP on the table (for racers, 20-40hp is big, even if it is only for a second or so depending on the gears)

again, the gear spacing is .85 and .8 for 4-5th and 3-4th shifts. take the RPM at redline, and see what the RPM drop is. see if lower shift points gives you more or less HP after a shift and compare. its really simple.

Mk

with your curves, it definitly pays a little to shift earlier, but only from 4-5th gear shift. (3-4th pays to redline or 7200rpm anyway ) that HP curve falls off pretty steep. so, shifting at 7k is not that bad an idea for you .
In this case, with the curve as it is, increasing redline doesnt buy you much, unless you had a 928 long gear box. :)

Now the red curve on the graph, pays for redline each shift, no matter the gear.
what was the mod that gave the HP gains, but hurt the shape of the curve, which obiously is a fantastic trade off?

red curve was pure stock pre-mod, final curve was done on same dyno in same weather after all mods were done, so what did what is difficult to say, it is final cumulative effect. increase to 7500 just helps to avoid cut-off before upshift.

most likely it is a combination of fabspeed xpipe 200cell cats and softronic flash. torque bump at 4500rpm is definitely softronic and it is pretty ****ty on a track as it happens quite sudden and if not careful car may spin but after 5K it became awesome - it really pulls very equally until redline. it was very different before those changes despite what graph shows - car did not pull in proper uniform fashion before, it was a definite 'drop' and tone changes - you can also see that on timing graph there - after mods it became much more stable.

again, on the other side - it may be specific to my car only as i got it in pretty virgin state with MAF sensor never cleaned so i cleaned it up from inside out literally then started adding stuff.

dirty maf and dirty stock air filter could be causing a lot of issues on that first curve, so, who knows.

Sorry, I didn't realize it was an obvious foregone conclusion and that you had an axe to grind because of some previous thread. I thought you were encouraging a discussion. That's not what's going on here, so I'm out of here...

Nevermind, I found it!!! :bigbye:

Scott

Here you go. At 7000RPM you have to make the decision as to rev up or shift. These options are highlighted in bold.

Edit- I did whip this up quick, so the units are meaningless without final drive etc. Also, the precision of the dyno numbers leaves something to be desired :)

An alternative way of doing it is to calculate Work with W=Pt and ignore the wheel torques but you still need to know the shift points.

In my 996 3.6L, I don't shift anywhere near 7000. Is that wrong? ;)

-td

Just a comment from the cheap seats....

Please stay on topic and avoid personal comments/attacks.

We won't be having a sequel to the events that led up to the last time I had to "take out the trash" in the Racing/DE forum.

Thank you.

:thumbup:

good graph. Its much easier to discuss with actual data. (even if it just proportional). I wouldnt go so far as to say its "meaningless", as that will not change the shift points of the respective RPM, but certainly would change the vehicle speeds.

wow, look at the power difference for short shifting. Now, could any motec data be found to dispute the advantage of taking the 3.6 to redline for max acceleration down a straight? looks like, even a 200rpm short shift costs between 20-40hp as was mentioned! :eek:

Thanks for the post.

Sorry, didnt mean to come off that way. I was just trying to show that the HP curve in the end is all you really need to show shift points which is much easier to see. BUT, the spreadsheet does give values to see the level of differences.

yes, the discussion is good.

Definitely there are somethings going on. I think I understand the raised redline, as when getting to the real redline, you dont want to bump off it. (not good for the engine to have a "miss" at 7000rpm. :) )

as far as the red curve, stock curve goes, you see if you short shift, even as much as 200rpm, it would cost you near 40hp!! (for the time it would normally take to get from 6900 to 7200rpm! 3rd to 4th gear shift) that is a HUGE loss by shifting earlier. Also, its really actually longer, because at the lower HP leve, you accelerate slower and you spend even more time at that lower hp level!

This is why this is such a great topic of discussion. you cant make statements about when to shift, unless you really know the HP curve (or torque curves).
And, look at that plummeting torque curve. common thougth would be that your torque is falling, why not shift? this is because as we have been saying, if you shift, the acceleration would be reduced even further!! :(

Apparently to some people. :rolleyes:

Clearly slowpokes like you, PedroNole, Viking, mglobe, me, etc etc etc could not POSSIBLY know anything, despite our real-world data & experience, when confronted by the theoretical world of a classroom instructor. :rolleyes: :rolleyes:








Professional Racing and Driving Coach

Is it wrong to want to lose 20 to 40hp by shifting early? If that is wrong, I dont want to be right! :)

now we have the actual data on a spreadsheet to make the point crystal clear.

Certainly on the street, or when in the lead in a race, it might be a good idea to save the equipment. But when going for best laps, you need to take advantage of all your potential. Performance 101 here.

I'm supposed to shift at 7000? My dog told me not to. I'm so confused now.

So, you are clearly disputing the data presented in a clear and consise fashion.

what real world data? Have we seen any of, other than a contrary to phyics sesation in your behind? This "noise" you speak of is a valuable resource to anyone trying to run a faster lap time. Just because YOU didnt see it in the hours of seat time, under racing conditions. :roflamo:, doesnt mean its not there. How about this. maybe YOU couldnt handle the extra power. You couldnt then, "bend" the car into the oncoming turn and you ended up slower. BUT, if you could, you would. Just something to think about.

If you are coaching with this logic and mindset, you are not doing anyone any favors.

You want to get faster, you need to use all your available HP. its not "noise" up top, as the chart and HP curves CLEARLY show.

Why dont you vist me in my theoretical world of the classroom at High Plains Raceway, so you can put your "Data" to the test! ;):D

"Luke, sense your feelings, use the force, read the torque chart! It will serve you well. dont circum to the darkside of "feelings" . those are for L. Richie songs ONLY..........." da da da, Nothing more than feelings, feelings of.........."

mk

Kibort, please learn how to use the multi-quote feature!

Why limit it to just that? :rolleyes:









Professional Racing and Driving Coach

as just an outside observer i can see what kibort is trying to say but i do not see what are you trying to say here. is there an alternative shifting chart to see?
just curious.

Baby steps Dave, baby steps.

PS-Someone email me a dyno file!

So wait....this chart seems to show that--GASP!--you don't really need to upshift at redline with this motor. But...but...but...how could that be? 42,000 defensive words of protest in 2 separate threads seem to indicate it is impossible! Zut alors!!! :roflmao:








Professional Racing and Driving Coach

Actually that chart shows that you're best off always shifting at 7250rpm(assuming that's the rev limiter).

:corn:Oh boy !

Not in gears 4 or 5, which is (not coincidentally) some of the gears in question in Brinkley's video.









Professional Racing and Driving Coach

No it's not, you make more transmission output torque at 7250 RPM in 4th gear than you do at 6060rpm in 5th gear. You also make more transmission output torque at 7250rpm in 5th gear than you do at 5970rpm in 6th gear.

Using my old car as an example, with a 7000rpm redline. From 1st to 2nd and 2nd to 3rd my optimal shift was 7000rpm, for 3rd to 4th it was 6800rpm, for 4th to 5th it was 6500rpm. So yes it's true for some cars, but it depends on the torque/power curve and gearing.

And yet, in the real world, what was true in your car is also true in the 996.









Professional Racing and Driving Coach

Hmmph. Well, I'm never going to shift at 7000.

-td

The real world is irrelavent in this situation because those involved real cars, the spreadsheet posted earlier were hypothetical numbers of a different car and my post is based purely off those numbers. Based on the info from the spread sheet, shifting at 7250rpm for all gears would be the quickest, for that car. Your post #42, which was in regard to that spread sheet, is wrong. For a 996(or whatever we're comparing at this point) I don't know the answer, but if someone sends me the info I'm asking for I'd be willing to find out.

Sorry, here you go! >>>>

really, my question too!

Let me know, ill send you one

Ummmm, are we looking at the same chart Dave??

all you mention, and this post and you still dont get it?? I give up......
maybe not.



exactly. I dont think Dave reads charts too well. certainly hasnt for years, why start now.

yes, in gear 4-5 transition. what chart or values are you looking at???

as a note, look at the drama that happens in the 2-3rd shift too. 100ft-lbs and thats before the final drive!!! you still stand by your "Data" and "experience".
I wouldnt lump the other guys into your corral, just yet.



yes, exactly right.

This tells us all we need to know about both these threads.









Professional Racing and Driving Coach

Taking my quotes out of context Dave, bravo. Way to change the subject.

in any car with a peaky hp curve, or even a flat top, its going to be true. your "real world" data is cluttered up a bit with other factors. If you have the data, show us a run to run comparison down a straight, with the g's listed at 7000rpm vs 7200rpm vs the post shift rpm. Because you failed to even see the difference on a very clear spreadsheet, something tells me you would have a hard time reading more complex information on the data aqu. output. Just a guess. in fact, you can try and find a dyno run that simulates your theory, but unfortunately, it would have probably had to be a 928. :)

anyway, as Greg posted, from 4th to 5th, the difference is from 204 vs the post shift torque of 180. 24ftlbs BEFORE even a rear end multiplier. so, more like near 100ftlbs difference! But, your data shows to the contrary. Hmmm, I wonder why. seriously. Or, i would like to really know the true comparison you did or what you are looking at, in order for others to not make this same mistake!

VR,

Have you looked at this article?:

http://www.allpar.com/eek/hp-vs-torque.html

It covers much of this. Here is another paragraph:

Not all cars should be shifted at the redline for maximum performance. But it's true for many cars. You can determine optimal shift points by graphing horsepower vs. velocity or transmission torque vs. RPM. Engine torque alone will not determine shift points.

That is what Greg is talking about and he is willing to do the math to show what the optimal shift points actually are.

Scott

even when he fails a task, he cant admit defeat. denial!

That's his style.

https://rennlist.com/forums/996-foru...light=996+dyno
This is the chart I used Greg. It was easier to get the dyno numbers off it than the one in this thread. Feel free to check my work.

Here are the gear ratios: http://www.californiamotorsports.net...oxster%20S.htm

There is no change of subject. All of these academic theoretical exercises don't change what PedroNole, Viking, myself, mglobe, and may others have figured out in the real world. Look carefully at 0:36 and 1:21 in this video, for example. I cannot IMAGINE why Darren does not shift at redline in these places. Hmmm.....clearly he has not been "educated" by the slowpoke of 50,000 words here. :rolleyes: He's ONLY doing a 2:05 here. :rolleyes:





As many of us said in the other thread, sometimes it makes sense & is faster to shift short of redline, and this is often true with a street based 996 motor. Which neither you nor Mark have seat time in. ;)

Ay ay ay....








Professional Racing and Driving Coach

Scott, check the video I posted. I am pretty sure an RSR is a pretty peaky motor compared with a street 996 motor, yet Darren is upshifting short of redline in at least two places. Q.E.D.








Professional Racing and Driving Coach

But the real question is does Darren shift at or before redline between turns 16 and 17? ;)

LMAO! Amazing how quiet the peanut gallery suddenly got here, eh? :D









Professional Racing and Driving Coach

VR,

Sure. I raced motorcycles (even more peaky motors) which are more sensitive than cars to traction changes in corners. With the higher horsepower bikes there were places on most tracks where I would up shift before red line so I would not upset the bike in the corner.

Would Mr. Law be shifting before red line if he were on the Mulsanne Straight? I don't think he would.

Unlike one other, I am not arguing absolutes here. I know there are good reasons to not shift at red line. But, if we narrow the scenario to accelerating down a straight, I think we can say that in that case, shifting early would not allow one to get down that straight faster.

Scott

But that WASN'T the scenario.









Professional Racing and Driving Coach

To be honest, with all the crap that has gone on, I don't recall the original scenario. But, as I said, I am not arguing absolutes here. I know there are good reasons to not shift at red line in certain situations.....

Scott

Your comment on the scenario (other thread) was:

"As he says, the 996 street motor generally makes more noise than power at the very top end of the range. I have spent some seat time in Spec 996 cars, and I find that my times are better if I generally upshift slightly short of redline. Plus, this is a bit easier on the equipment."

:confused:

And that was my ONLY point (as with Pedro, Viking, et al).









Professional Racing and Driving Coach

And....? Where is your confusion? The power graphs show the power falls off at the very top. So...where is your confusion?









Professional Racing and Driving Coach

I thought you were saying that accelerating down a straight wasn't the scenario where you would short shift. If you meant that you would recommend to do it so the car is not upset at turn-in or whatever other scenario involving weight transfer, etc., then all this is miscommunication I guess...

Edit: Sorry if I wasn't clear again... accelerating down a straight wasn't the scenario as compared to your initial suggestion to "generally" short shift.

I'm not going to comment further, I know what I've posted is correct. I couldn't really care if you agree or not, it's just another advantage I have against you and your clients. If you want to have an actual conversation then email me, but I'm not going to play the 'look at this video' and 'I have data but won't post it' game.

Of COURSE you do, Greg. :rolleyes:

I couldn't really care if YOU agree or not. When you and/or Mark get some seat time in cars running street-based 996 motors, you can rejoin this conversation with some credibility...just as I said at the outset of this...and then you will understand.

Until then, enjoy your Sour Grapes Club membership and your "advantage".

Too funny.








Professional Racing and Driving Coach

I feel the exact same way Greg.

Do I post an answer that could help a number of RL'ers ?
Or
Keep my mouth shut and keep coaching guys that use the info and seem to go faster than most.
Debating with Mark, who is never wrong, is not even a considered option.
Or
Maybe I should just give a clue to why it works so those that are smart enough to figure it out and use the information can and will. - While others will follow those that sit online and type a lot about how much they know with no real experience, data, dyno time, time in other vehicles to prove or disprove what they preach. After all, if it's on the internet, or written somewhere it must be true........

Ding ding ding! As usual, you and I are on the same page.









Professional Racing and Driving Coach

Sure !

As an Rennlister club race amateur, I thought that this forum was a good way to get useful info. May be I should look elsewhere (private coaching only ?) if the most experienced people here can't explain why this other person is wrong...

...;)

Here's my 996 that I run:
(stock gearbox with these ratios:
1st gear 3.818
2nd gear 2.20
3rd gear 1.516
4th gear 1.216
5th gear 1.024
6th gear 0.841
Final drive 3.444)

Since you're asking, I shift below redline for "theoretical longevity" reasons...

Just so everyone that doesn't know VR and I understands ....... VR and I don't always agree.

We do share a common belief that trial and error with the support of data via in car data, dyno's, etc allow us to provide a better understanding of what works and why in the real world. Which ultimately allows us and our respective customers, students, and friends to see better ultimate results.

This whole thread reminds me of a conversation I once had with a (claimed) thermal engineer regarding why a car without a thermostat actually ran hotter than it had previously with a good thermostat.

There is a lot of useful info on here, but as racers are a competitive bunch you can't always expect them to just totally give away all their secrets. My recommendation would be to try both ways and see what works for you, in your car, on your tracks, and do it with data that can allow you to see without a shadow of a doubt which works best for you. - Ultimately, thats all that matters anyway.

I'm here for the friendship and because TV bores me. I coach a number of people, I maintain a number of cars, and I have also built a few cars over the years. I'm not here to advertise or get new customers or even inflate my head. Hell, I don't even have enough hair to cover my head now, I couldn't afford for it to get any bigger. :D

Have a good evening.

I am sorry you got the wrong impression: I have no desire to explain why "this other person is wrong" not because I don't want to be informative, but because it will only generate another avalanche of enormous, overly wordy and condescending posts from him, usually 5 to 10 in a row. And none of us can take any more of that.

Here is what I suggest: look at the graph that garrett376 posted above (nice RWHP by the way!) and then email me, and I will give you my view of why in many cases upshifting a street based 996 motor short of redline can be much faster around a track: dave@racecoach.net

And then you can make up your own mind.








Professional Racing and Driving Coach

Dave, I have said nearly a dozen times, and others here can back me up certainly it DOESNT always pay to redline or maximize HP in areas of a track where traction or control are an issue. we are talking straight line, and notice Darren on some of the key straights, pegging the rev limiter before braking zones off a straight..

You have proved you are not being careful enough to evaluate the data posted. here. by reading the graphs of HP curves, and there are many of them, It is HIGHLY unlkely that somehow YOUR 996s that you were driving had some other shapped HP curve. more than likely, they were even more peaky than on the dyno due to ram effect and cool air intake. regardless, you are double talking, forgetting and not able to understand the information that is for others, very easy to grasp. you mention falling HP curve, but for some strange reason, you forget that the shift to the next gear has a less mechanical advantage. In the the end, the torque spread sheet or the HP curve has ALL the answers based on the .8 to .85 RPM change for a shift.

I dont get it. why are you fighting it. Its clear you dont even remember your own statement of short shifting due to the engine power at the top, just being "noise", when in actuality, that noise is power! and that POWER is more than if you were to shift.

To say that a top pro is short shifting, in a particular video, and to say that it must be "correct" is nuts. that car has so much power, and he is ripping around the track at break neck speeds, it might be a lap where he is just trying to be comfortable.

On that same side of the coin, your faster laps, with short shifting could have had a million things going on that skewed you times, certainly, short shifting wasnt anything that could help, but only hurt your times. take that motec, make a perfect lap, and use redline shifts vs non redline shifts and you WiLL have a faster time. basic physics, and everything to do with reality, not your experience.

So, there the scenario! you got it. we have said many times, forget about turns, turn ins , transitions, etc etc, ONLY straigth line performance.

I dont think you know what your point was. I know what you are saying. you are talking about short shifting through turns.
Now, HERE is your CONFUSION. I hope you understand WHY you are confused. I dont know why im going to help you , but I am. probably because it is so sad you sit back, spew errors and just say, "your wrong" for your defense. Anyway, here it is. The power falls off up top, but its still at a level, where a shift would produce LESS torque to the wheels. This is why it pays to shift at or even sometimes, beyond redline. factory redline is usually safe, and sure, you are working the engine more than if you short shifting, but in racing, as I said, you are using the equipent to the max to go as fast as you possibly can (qual or a tight race), or you are just driving around for fun.
If you want to win or post a top time, you need to shift, usually at redline, unless your engine has a HP curve that doesnt pay to redline, as that does exist. the 996 isnt one of them.

my comments, as much as you want to poke fun at them or my wordy data enclosed responses, it doesnt matter if you run a 996, ferrari, 928 or a VW bug, if you have a peaky HP curve, you shift at redline to maximize acceleration.
Ive said it once Ill say it again.
acceleration =power/(mass x velocity) this means , at any vehicle speed, acceleration is directly proportional to power. (or as greg said and posted, torque at the wheels.)

Im beginning to think this is all a mistake. Now when I race VR, he will be taching out the 944 and give me more of a run for my money. :)



that sounds interesting, but in a 928, your engine will overheat without a thermostat. :) It does it because without it, the dual function of the t-stat of restricting flow and directing flow, is removed. the directing flow part, being removed, allows for no flow and the engine overheats.


Do you think anyone wants your opinion now, based on your inability to even read the charts and give us the gears where you would want or not want to short shift. YOU clearly said, 4-5th gear when in actuality, the torque, power or whatever , was less post shift if you did.
AGAIN, we are not talking about transition turns and cornering , traction areas of the track. ONLY straight line acceleration.

Now, you have a copy of what you said. Care to recant? How about this. give me your reason and I promise not to respond at all. That way , if it is some revelation, we can all benefit, and you dont have to listen to my critisism.
So, what is the reason you would want to short shift on a straight based on the 996 HP curves presented here?
If not, would someone please send a dyno chart posted on this thread to VR Dave, so we can hear this revolutionary reason? I guarantee, AGAIN, I will not post again in regards to any post VR makes from this point further! thats a racer promise! :)

Please tell. Im really curious. seriously!

with this gear box set up. Ill put the % rpm shifts below:
1st gear 3.818
2nd gear 2.20 57%
3rd gear 1.516 68%
4th gear 1.216 80%
5th gear 1.024 84%
6th gear 0.841 83%
Final drive 3.444)

what this means, is that for each shift of a gear, the resultant RPM is x% of the prior gear RPM.

look at that chart that shows rear wheel torque, and then use the 3.44 rear end multiplyer to see how much torque you lose by short shifting. in some cases, over 300ft-lbs lost by a short shift , as measured at the rear wheels. :eek:

A quick thanks to all those who sent me emails overnight. I hope my reply this morning answered your questions in the context of this discussion as well as Brinkley's video in the other thread.









Professional Racing and Driving Coach

Just for discussion's sake... with this engine (dyno below) I shifted the car around 5500 based on "feel" - this engine didn't pull past 6000 very hard and felt stronger in the next gear at lower RPM instead. I didn't need the dyno graph to realize the power drop as it was easy to feel. The new engine is obviously more fun - it's an x51! :)

I usually try to shift my little 3.4 (270rwhp) at 7k although it will rev to 7400. It all depends on the circumstances and specific corner....

I definiitely short shift at a specific corners where too much torque could push me over the edge. Backside of Cotton Corner's at Buttonwillow comes to mind as it's a off camber, downhill turn into a short straight that has sent many cars off into the desert or worse. Another example would be T8 at Willow Springs, a high speed sweeper leading to a short straight and brake zone. I shift a touch early into 6th approacing that turn as my max grip of 1.6-7 G's is easily obtained in the taller gear at the lower RPM's. Conversely, I take it to 7200 or more in 4 & 5 coming out onto the banking at Cal Speedway where you absolutely need to stay up in the power band to make it around T1 & 2 at your max speed. So my $.02 is that your shift points are relative to the track and the turns you're facing. If I have a big lead or I'm way behind I take it easy to save the mechanicals and tires. But what the hell do I know.....

The best way of determining shift points is to use the completion backwards principle. Starting from the point of maximum velocity just before braking, compare speed and gear and minimize back in reverse order the QUANITY of shifts above the torque curve you wish to employ.

so, now after this discussion, you can now see how much time you are leaving on the table. If you shift your engine at 5500, from 3-4th gear, the resultant rpm puts you at 4400rpm post shift. thats 235hp down to 200hp. shifting later, gives you a 250hp shift ending up at 235hp. at first glance, thats a 20hp diff of average HP. But, that doesnt tell the story. you shift at 7200rpm , near 250hpand you drop down to 235hp. (otherwise you shift at 235hp and drop to 200hp. This means, you are really down near 50HP . Youre not the first to be fooled by your butt dyno. :)

Now, your graph makes it a lot more complicated, because of the dip. this is where some area under the curve work, or HP-seconds (J) needs to be taken into consideration. certainly the shifting early is killing your performance by 20 to 50hp , without question.. I could give you more accurate differences if you really think you need it.

my advice. fix that dip in the curve, if possible. shift at redline for best straight line acceleration.

Edit: a summary of the above, is that by shifting at 5500rpm, you are almost 2 full gears down post shift, and thats a rear wheel torque difference of nearly 50% !!! Its one thing to see, feel and hear engine torque loss at the high rpm, its quite another to incorporate gearing and power (multiplied torque) and make a correct gear selection opinion.

The "best way"?? I dont know really about that, but the easiest, (which I think is the best) is to just what we are talking about here. just maximize HP as best you can by getting the greatest time spent in the highest HP range, and you maximize hp, regardless of top speeds on a track. usually, as we see with the 3.6L 996, this means shifting at near redline. (whenever possible, and you wont be upsetting the car in a turn, transition, etc.)

The discussion really is about straightline acceleration. maximizing acceleration of the engine when you can. sure, a short shift in areas like you say, similar to coming out of the corkscrew for some cars, and certainly coming out of the "wart" at thunderhill, where redline WOT, might just not be possible. (thunderhill turn 5 yes, need to short shift, corkscrew, not anymore)

anyway, its a discussion if the top end of the RPM curves are noise, or power. by definition the curves show power, so this is very easy to see for the semi trained eye, with access to a set of gear spacing %.

Please send me this information if you recieved it via PM. I will not discuss on this list. I am curious what we are missing here if we are are incorrect in our calculations. My guess is that short shifting from VR Dave's perspective, is related to traction or car control issues at certain parts of the track. It would be a revelation, if any straight line acceleration hypothesis detailed out in our discussion, can really be challenged.

Mark

I've decided that Mark and Dave are like North and South Korea. They both speak the same language but are not having any sort of intelligible conversation. There's aspects of both positions that are correct but neither seems willing to concede that anything the other says has any merit. It's a shame really because there's some very good racing technique information that people could draw from the contributions of both guys but there's so much crap to wade through it's not really worth finding the valuable information. I think jrgordonsenior sums it up pretty well though.

Funny. yes, racers all will have different take on style and trade offs for maximizing performance. Its the way of sports. I have a 1000 things I would do different that dave on the track and have logical, thought out reasons for them, and IM sure, dave would have the same. so many trade offs in all areas, and in the end, I respect most all of them and certanly would try them all as well. HOWEVER, there is only ONE thing I disagree with completely .
That is, when an engine makes a hp and has a HP curve, you can easily use that hp curve (based on gear spacing) to determine shift points. I really dont think this is debateable. really, and so far, in the 100s of pages of this stuff, he has never put down one single solitary bit of information to the contrary, other than to say I am "wrong". So, he fired off some PMs and emails this AM to explain his thoughts, and Im really curious as to what they would be. :rolleyes: Seriously, if you make less hp after a gear shift, you are accelerating at a LESSER rate. PERIOD. And I have to say it again, because it is glazed over, this is not applicable during traction or handling related issues on the track. ONLY straight line performance. He says he shifts early due to that engine rpm area just being "noise". I say, that "noise" is greater hp , thus greater ability to accelerate even if HP is rapidly falling off . (if the falling off is greater than the post shift HP.) easy to prove in theory and reality. you cant fool Newton! many have tried! :)

I think Gordon did sum it up perfectly and its what we have been saying all along. Most of us anyway. shift at redline, unless you cant due to traction or upsetting the car, so why not save the engine if you cant use the power. totally agree with that and practice that myself.

VR Dave Scott said:

"...The 996 street motor generally makes more noise than power at the very top end of the range. I have spent some seat time in Spec 996 cars, and I find that my times are better if I generally upshift slightly short of redline. Plus, this is a bit easier on the equipment."

What you call "crap" is--from me at least--my total unwillingness to post the proprietary data of my clients, and thus sell out one of their competitive advantages. Despite Mark's 90,000 word avalanches, my statement, which he has bolded and posted many times along with my name, is still true. Garrett's graph shows that power falls off pretty dramatically just before redline with this particular street 996 motor...and it is simply slower to try to use a falling power curve rather than a rising one.

Again, in what we refer to as the real world, things are often different than in what folks can Google. So if you want to call that "crap", knock yourself out. I have nothing to prove here, whereas Mark apparently does. Folks here can make up their own minds.








Professional Racing and Driving Coach

So, Dave,
Im still really puzzeled. you have kept us in the dark regarding your revelations of how to bend the laws of physics, so just clear up one thing that you already said, and was corrected by many of those participating in this thread.

The reason I bring this up, is that if we find our what part of the chart you are looking at, maybe we can figure out what you mean. I know you are not a dummy, but sometimes your ideas and thought process is not very clear. So, im sure you have a good reason for saying what you say below. in otherwords, clearly, beyond a doubt, you DO need to shift at redline to take advantage of the available HP of the 996 engine. why did you say you dont?

curious......
..>>>>>>>>>>>>>>>>>>>>>
VR Dave Scott, said:
So wait....this chart seems to show that--GASP!--you don't really need to upshift at redline with this motor. But...but...but...how could that be? 42,000 defensive words of protest in 2 separate threads seem to indicate it is impossible! Zut alors!!!
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>




Now, I also want to hear from the 9 soles that also think that the upper rpm activity in a 996 engine is just "noise" and it pays to short shift. Why do you think this, when the data would suggest otherwise? Do you just think its not a big deal to lose 20-40hp for a second or two?
that saving the engine from extra abuse for that short of a gain, is not worth it.
If so, then the fastest possible lap time, really isnt that important to you.

Im really curious, because I certainly understand the other 10+ listers that will follow VR off a cliff, thats just natures way. some of us, just have blind faith. :)


One thing for sure, this could help us on race day (those of us that dont believe VR), in that there are 20 racers that follow him blindly, or dont understand the concepts, so if 50% of the racers /followers, are out here, thats 5 guys that will be at a distinct disadvantage when it comes to race day if they are already close on power! They will probably be blaminng their corner balancing or their wing settings when they lose! :)

[QUOTE=JustinL;8285965]Here you go. At 7000RPM you have to make the decision as to rev up or shift. These options are highlighted in bold.

QUOTE]

I rest my case. Korea will never be reunited. Have fun bickering fellas...

ki•bort \ki-ˈbȯrt\ Verb
1. Render obscure, unclear, or unintelligible.
2. Bewilder (someone).
3. Process of obscuring so as to hinder ready analysis.

To "kibort" a thread: to make meaningless, unwieldy and not understandable to lay persons.

"A great effort was made to kibort the analysis. In sum, we were left baffled and bewildered.”

That is the REAL difference here with you vs me, Dave. I'm here to help, and you are hear to premote yourself. Very clear now! knock -your-self-out.
You dont have a porsche, you are not contributing, really, unless you are gettting paid. Hmmm, very telling.

I think any of us in the know, now see your problem with the concepts. you are confusing a falling HP curve with a post shift reduction of HP. just because HP is falling, it doesnt mean that you are accelerating less than a rising HP curve. (kind of reminds me of the one confused sole that didnt understand that when you lift to shift, you actually decelerate! he was confused with the force, and momentum concepts) you call it google, i call it an expensive education, and in the end, the education really did involve "real world" information too.

The fact that you think a falling HP curve is slower (less acceleration) than a rising one, is amusing. really. now, you cant tell us why, because its your proprietary information, and their "competitive advantage" . Thats funny and very convenient. I hope , no , Pray, i meet one of your students in one of my races this year! :) Better yet, YOU ! High Plains Raceway! :burnout:

Anyway, Garrett's graph does fall off before redline and that fall off is still showing more hp available than a post shift level. PLUS, if you are approaching a braking zone, and you might not have to shift as you go to redline, you now shift and lose not only 300hp or so, but negative braking 20hp for coasting. Put .3 to .5 sec of braking power, for that time sequence, into your equations for acceleration where you have decelleration for a shift during that straight.


So to summarize , and make clear to anyone that wants to use YOU as a racing resource, to maximize performance, you think the acceleration of a falling HP curve at a higher HP, creates less acceleration than a rising one with a lower HP level. Got it. :roflmao:
And, that the point at which the rising HP curve is caught by the next gear being at a lower HP, doesnt mean anything either? Got it.

VR, this really shows your value as a coach. First . inability to really understand the information or read a graph correctly. Second, inability to learn something that you may have have not known before. Nothing worse than a player or coach with a closed mind.

Another day, yet more insults & personal attacks, Mark? Aren't you the same guy who has repeatedly whined about same?

No wonder no one wants to discuss anything with you.










Professional Racing and Driving Coach

which ones of these dyno runs is VR Dave Scott, refering to?'

Garrett, are both of these from the same car, different engine, or different all together. you claimed both of them. :)

Eitherway, both pay to shift at near redline, if redline is 7300rpm.

why? because the HP after the shift is much higher than shifting earlier , and the pre shift level of HP is much higher than the post shift level of HP.

bottomline, if you ever, putting down more power, you are accelerating faster. its really that simple. (and thus you will be putting down more rear wheel torque)

by the way, take the graph numbers and multiply the values by 3.44. that will give you the real differences in torque found at the rear wheels if you short shift. basic physics! some differences are near 300ftlbs! by short shifting.
do that on the main straight of willow springs or Cal speedway and you are going to be left in the dust by someone that is NOT listening to VR. :)

..

Not to add more fuel to this fire, but I'm still not going to shift at 7000 RPM in my 3.6L 996. Doesn't seem like a good idea...

-td

Attachment 511632

No fuel on the fire...., good discussion.

why is it you feel its not a good idea. do you have the HP curve handy? or did you post it before?

remember, all of those values below are multiplied by 3.44 to show the real difference in torque to the rear wheels.

why does this go to 8200,is this not a street 996 engine, or something else. what redline are you refering too. redline stock or this new redline of 8200rpm.

what are the highlighted areas meaning?

Mk

news flash, this discussion isnt with you Dave, you have not posted anything worth looking at. and infact, you have only commented and made errors of your assesment (verified by greg and others) of the main thrust chart. When asked about your reasons, you just bow out and say , "proprietary". You then correct yourself, and say, "maybe for 5-6th gear as was the main issue with Brinkely." but, when called on that as well, you just remain silent , start back pedaling, and then refer back to your "data" for truth.
You are like a religous zealot!
So, you havent really entered into the discussion, except for saying that we are "wrong".

no whining here , just disucssing. :)

Also curious what engine this is. GT3? What do the blue highlights represent? This looks like a car that is very well geared for it's power delivery.

Poll needs an fifth option:
5. I drive the entire track at redline in 1st gear to sustain maximum wheel torque.

Speaking of North & South Korea: The only thing more frustrating/entertaining than this thread would be watching a death-match between Sarah Palin & Kim Jong Il, each armed with nothing but goose down.

TGIalmostF@RL

for a autocross that would work. :)

its the same gearing as the 996 3.6, right?
where would you shift it if it was your car? (on a long straight that is! ) :)

If someone else is footing the maintenance bill... then 8200 would maximize acceleration all else equal. Though I think the 996 GT3 has gear dependent rev limits.

Discrete components of curve are posted in my excel sheet above. Some of the items are extrapolated from the curve.

TORQUE: I have a fairly flat torque curve:

• 240@2600 RPM - generally rising to a high of
• 289 @ 5000 RPM (high) which is a typo in my spreadsheet, but it's too late to fix it now), slowly dropping to a second low of
• 240 at 7700.
• There are a few little crests/valleys in the graph.

HP [corrected] :

• 120 @ 2600 rising to
• 280 @ 5000 and on to
• 373 @ 7321 and then tapering off.

This is a street GT3 with a stock 3.6L flat six, pushing 380 HP [factory claim]. The stock redline is 8200.

Green is max torque RPM [5000 RPM with 279 (typo as noted above)].
Grey is gear down location [i.e., shift from 8200 in 1st results in 4500 in 2nd]
Yellow is Max HP @ RPM [373 @ 7300]
Blue is overlap with max tq from next shift.

-td

Got it. thought it looked a little stout and high strung! :)

anyway, we were talking 996 street, but, you have a couple of short shifts noted and I think you would be better served by redlining at 8200 and I posted some pointers on your graph.

also, a graph of the 996street motor and why we should shift it at redline as well

the red boxes are redline shifts
the blue boxes are 7300rpm, incase this was a 996 street motor with mods
the green boxes are it looks like, your short shift points.

on the second graph, the points are self explanatory.

From Garret with RPM drops vs GT3:
Here's my 996 that I run:
(stock gearbox with these ratios:
1st gear 3.818 vs GT3 3.82
2nd gear 2.20 57% vs GT3 2.15 56%
3rd gear 1.516 68% vs GT3 1.56 77%
4th gear 1.216 79% vs GT3 1.21 82%
5th gear 1.024 84% vs GT3 1 82%
6th gear 0.841 84% vs GT3 .85 85%
Final drive 3.444)



can you post your GT3 street hp curve??? thanks

Mark

Blue is information only, you are not required to move over. ;)

Yes, these two different dyno graphs are from the same "car" but with different engines installed. Due to the "dead" engine that has no guts above 5000rpm, I swapped engines between this car and my street car since the x51 engine won't get me to work any faster, but the increased power is a lot more fun in the track car. ;)

This is an interesting discussion (the technical stuff part of it)... gives me something to think about at the POC willow springs races this weekend!

That's been my reason for my earlier shifting: my current (or future?!) race budget doesn't account for engine work, nor does my means for getting home at the end of the race weekend!

And FYI there is more to a fast lap time than just maximized acceleration. Unless you're a drag racer... ;)









Professional Racing and Driving Coach

Gearing is not the same in the C2 and GT3.

Here is a graph.

-td
Attachment 511650

VR, i couldnt agree more. its all the factors optimized for a fast lap though. sure, brakes and tires are cheap when there is accelerated wear from pushing it . however, i agree, if that extra 300rpm costs you an engine 10 hours earlier, you have just de-tuned for budget reasons. nothing wrong with that.

But , we are talking about fast laps, no excuse, no holding back, fast laps, right?

:cheers:



I posted the differerences of the gearing on my post. pretty close though! I was surprised.

Now, the graph. You interpolated the 7500 to 8200rpm data?

based on the curve, it most certainly pays performance dividends to shift at redine. if you look at the torque lost by short shifting, you can see those numbers can be as close as 10-100ft-lbs, but remember, multipy that by 3.44 and you get the real difference at the wheels.

Btw, its so much easier to do a visual "integration" by looking at a graph. you can actaully see the trade offs. with the chart, you dont know what is under it, and you really need to integrate the values to get the answer you are looking for. just by looking at the curves and knowing the rpm drops are 80-85% of post shift rpm, it is clear you always have more power available by shifting as high as possible. I dont know about redline with this motor because its a guess as to where the HP curve goes, but generally, it continues to go up and doesnt fall too much. Here is a GT3 cup and street dyno

..http://1.bp.blogspot.com/_jgyugzLdbn...ke-it-stop.jpg

Dave, we are discussing something, do you mind?
Do you always have to be the center of attention? :rolleyes:

I was directed to this thread for a different reason, but I did read parts of it. Can I just ask a quick question? Okay . . . I have years of experience in the Spec Miata class. I know that each car might vary, but generally the 'sweet spot' comes in around . . . . 6500. It redlines, however, at more like 7200. From what I have read and from graphs I have seen, the oomph (sorry for the lack of technical term) starts dropping off once you pass that sweet spot, and thus it's time to shift. Anything past the peak torque (I guess that's what it is called) is just wasting gas and you won't continue to accelerate. I hope I'm getting this across properly.

So . . . is that basically what's being argued here? Or are you gonna make me read eight pages of half argument, quarter speculation, and some graphs. :) Just tell me if I've got the basic idea correct. I've not messed with my Porsche on the track yet to get a feel of where its power band (sweet spot, as mentioned above) starts and drops, so I guess there's a chance there's a difference in its inherent behavior than with a Miata. But that's the experience I am drawing on -- playing with Miatas for many years. I get to play with the Porsche (hopefully) in March at Barber. Hopefully I can get something out of all this way-over-my-head conversation. :D

Oh! Ooops. BTW, I don't fall into any of the four choices in your poll. As I tried to explain, I try to find the sweet spot and shift just as it starts to drop off. Where that is on my 993 I hope to soon find out. No it's not a 996. But it's still got a 3.6 litre engine and I like it better (not that I'd turn down a 996, I just wouldn't trade my 993 for it). :p Lol.

shorter thread:
MK: In the absence of any conflicting priorities, shifting a 996 at redline produces max accel.
VR: Many tracks involve conflicting priorities which make the above shift strategy counterproductive vis-a-vis laptime.

Both true. Neither takes a genius.

Can we please be spared a 9th page?

And ask us to behave like adults? Surely you jest! :D Oops . . . this might be on the ninth page. ;)

Bonster,

You are asking the exact same question that many have toiled with.

There are several things:

max torque = meaningless for our uses of performance
max HP = Only an indication of what power is available in that range
sometimes it falls at max rpm (redline) and other times, several 1000 rpm earlier.
flat torque= means nothing means HP is rising. most engines have max Hp when the torque is falling. Hp is torque x speed /5250.
HP definition = Hp is the max ability for the car to accelerate at any vehicle speed.

So, in most cases with a rising HP curve, torque is flat. a flat hp curve ,and torque is falling and falling fast. :)

so, if you look at the HP curve, you will see it rise to some peak and then start to fall. sure, when its falling its making less hp, but the entire discussion is about when to shift. you shift as soon as the falling hp reaches a point where the post shift HP is equal or greater. (usually slightly greater, as there is time for a shift that has to be taken into account). This means you might feel like acceleration is falling off ,and it is, even if you are at max hp, acceleration fall at the same rate that you are accelerating. But, when the HP falls off , that lack of acceleration is even GREATER. the question becomes is it even worse if you shift into the next gear (less mechanical advantage) or stay in it til redline. That is the million dolllar, 9 pages of this list, question. :):cheers:

so, in the end, peak torque even peak HP are not required for bearings on when you should shift. its the shape of the curve and the spacing of your gears.

This means, with any high rpm engine, in generally pays to peg it to the rev limiter, unless doing so upsets the car in a more technical part of the track. by doing this, you maximize wheel HP and thus maximize acceleration at ANY speed you are at on the track.

(

Can we just assume that Mark's point regarding a 996 car could be solved in a straight line drag race. Surely what ever car wins that race would prove this single idea?
As for being faster around a racetrack there are a lot more variables. Apart from the physical attributes of the car itself, perhaps the driver goes faster by changing at a certain point
as opposed to another. Looking at the film of the 935 doing the hillclimb recently showed in certain places he certainly 'short shifted' and the car appeared to take a sit and accelerate
faster. https://rennlist.com/forums/racing-a...light=935+porn
There are charts and graphs AND there is butt dyno and times...both can co-exist and both might be correct at different times. Probably the best thing to do would be to take some data
with the car in question on the turns in question and put this 'all too short' thread....

I think Patrick's assessment is the best by far. You can't always take 'written in stone' data and make it apply to everyone. And you can't always have one answer for any question, especially when it comes to racing/track driving. We can only really discuss our own personal results, compare and contrast, and hope to improve. At least, that's what I think. But I can't be right all of the time. ;)

C'MON PAGE 9
:jumper::jumper::jumper::jumper::jumper::jumper:

Man, you guys can really get into it...

9th page??

sh*T That didn't do it.

Sh*t it did do it!

EPIC!!! We now need to go for page ten!!! :roflmao: Just to piss some of these guys off. :roflmao: Yes, I am a bad influence. You should see me after I've had a couple of whiskeys. :D

"The best way of determining shift points is to use the completion backwards principle. Starting from the point of maximum velocity just before braking, compare speed and gear and minimize back in reverse order the QUANITY of shifts above the torque curve you wish to employ."

The "Completion Backwards Principle" , wasn't that an album by The Tubes in the mid-eighties? I Loved those guys, they ROCKED, finally this thread has merit. :rockon:

I have an eerie feeling we've been here before...

Too bad this thread is being filled up now with useless posts, as I've appreciated the interesting discussion and learned about things I had not considered or thought about. So, thanks!

Actually, you can. (somethings are set in stone and easy to apply under all conditions)

What you missed by not reading the last thread and the 9 pages of this thread, is that we already qualified the question, but saying we are not talking about any other place on the track BUT the straights. Some have said that they shift early, generally, because the engine is just making "noise" up top in the RPM of a 996 street engine . Some have also reviewed the force chart and made some incorrect comments, as anyone could (not really clear to understand), as it showed that in any gear, short shifting, compromises accelerative forces. Actually quite substantially. (between 20-40hp in some cases for times near 1-2 seconds!)

Thats is the great part of this discussion, even more so than drag racing, it doest incorporate ANY variables, really. as long as you have a dyno sheet and a set of gear ratios, you know when to shift your car for max acceleration.

Again, as long as you are not traction or control of the car, limited! :)

The only possible problem with that logic Mark is that even though you qualify this question by saying it's on the track but ONLY on the straight, the straights are preceded by a corner. Now what about if the person who 'short shifts' (itself a grey area term) on the straights also shifts differently to you who would be redlining down the straight. Mr SS might be coming out of the preceding corner faster than you because he upchanged and was gathering speed earlier than you. This is hypothetical but it is a possibility.

Overall if all you are saying is that it's faster (in a straight line) by holding on till redline in a car that has power all the way to redline vs upshifting to a lower power level, then yes OK that sounds clear enough.
After that it becomes very subjective IMHO.

I guess, Patrick, that now would not be a time to ask about what happens when you introduce forced induction? With that, I am running for the hills. :D You guys be good and don't get caught if you're REALLY good. Lol.

Don't open that box please! To be fair I think this discussion started and can be kept just about a certain 996 spec motor.....although I guess if you really want to stretch that concept, by repeatedly shifting at Redline there is the very real chance that you are going to induce more heat into the motor and reduce power which might just slow you down the longer the race goes for (moreso with forced induction too). Not to mention added wear on components that might add an extra pitstop?? Just saying....

the preceding corner has no bearing on anything. if i dropped you from space on to a straight on a track, and you said, "wow, im racing and floor it " you would shift up until redline, because that is where you get the greatest overall acceleration. remember, this is not a discussion about modulating power, traction , set up, style, nothing, however, If I put you in a car that had a ton of power, and you followed my direction here and you were not used to the power, you could overcook entry points to turns and have a much slower lap time than someone else. But, if you can "Handle" the power, you will be faster down any straight. Also, there is a high likelyhood that SS guy, might shift 3-400rpms and then have to down shift for a turn, rather than pegging it to the revlimiter. this will be a double whammy advantage. more power available up top of the RPM, (even though the Power is falling with RPM rising) , and they have lost time with a .3 to .5 shift time , where this is a negative power, not low power, not 0 power, but negative power. (actual decelleration happens between shifts, unless you have sequential gear boxes, and then its slight if any at all)

yes, this discussion has been only on the straights, and "is the rpm after peak hp " just "noise in a 996 street engine??? :)
The answer clearly, without any possible challenge , no. its not noise its more power than if you shifte into a lower gear. (more often than not with a high strung motor.) Now, get into V8 land, or turbo land, then yes, it might pay to short shift. This is why, no one can really tell, until you look at the HP curve and know the gear spacing.

all you need is the hp curves cold and heat soaked to tell. many turbos fall off in power after peak HP pretty rapidly, but some do not. the curve and gear ratio will tell all.

But, what I can say, is shifting by butt dyno certanly is not a good way to maximize acceleration down a straight. in the turns, it is, because you can certainly feel the drive wheels giving way. This is part of the craft of racing. straight line has no craft, only in the shifts if you are operating a clutch. :)

mk

If you dropped me from space I'd say something like "AAAAAAAAAAAAGGHHHHH-SPLAT!!!"

In all fairness you can't take out the preceding corner to isolate the point you're making. You have to include them otherwise you're talking about a drag race. As for losing time due to shifts, well that's true but if I shift from e.g. 3rd to 4th through a long sweeper and the car sits and settles into a better line then I'm already in 4th while you're coming out of the corner and perhaps hitting redline and shifting into 4th on the straight. At this point who is going faster?

I get your point and I don't disagree in some principal but I just don't believe in absolutes unless you get totally unadulterated data from the car in question on the track in question under identical circumstances / conditions. Not impossible. Be nice to see.

So if I am driving a 400 hp LS1 motor or a SRF I should shift both at redline ?
Any SRF drivers care to jump in ?

Feel free to jump on this one VR, I don't have time to play here as can be seen by the time of morning that I am currently typing this response, just before going to bed.

Oh , wasn't there an epic thread some time ago where it was argued,discussed, debated, that torque was not what mattered, it was all about the hp ? Yet now suddenly torque is what we are discussing as being important. How did that happen ???

There is another element here that has been forgotten I believe.
Bueller, Bueller .......

onefastviking,

I have blissfully missed a lot of posts in this thread because I have a certain poster on my ignore list.

But, I will say that what matters for best acceleration is not torque at the engine. What matters is the torque at the wheels. The transmission multiplies the engine torque.

To quote some text from the web site I posted much earlier:

Shift to maximize engine POWER, not engine torque! This is *exactly* the same as saying "shift to maximize transmission output torque".

Again, this is only valid if you are trying to maximize acceleration. If you have other concerns, you may not want to maximize acceleration while accelerating.

Scott

You're joking, right???? Please tell us you are joking, Mark....

Viking, why should I bother any more? Your comparison of LS1 vs SRF is a valid one, and we both know what the answer is. And my private replies to the numerous email queries I have received on this issue have included a discussion of the role of torque as well as HP. But you know as well as I know that ya can't tell mark anything. He will never, ever, EVER back down nor admit there could ever be any fault in his Googled "logic", despite the obvious fact that he has zero seat time in type.

So why bother?








Professional Racing and Driving Coach

Yup. That is about all that needs to be said. Amazing that some will make dozens of posts with graphs, posted over and over and over (like many, I can't manage to actually read all that crap when someone cannot make clear point without attacks).


SRFs are interesting. Redline is pretty low but you can actually go past it under power as the valves float. They are also slow to shift so there are many places where you might find it better to hold the lower gear, rather than go through a quick upshift and an almost immediate downshift.

Also, there is a HUGE gap between 4th and 5th (not as bad as it used to be as I think they allow an optional 5th ration now). That really makes you want to hold 4th as long as you can, because you will lose acceleration in 5th to a great extent.

Without knowing the gearing of the LS1, impossible to say. With the SRF the shift points are well before the red line. Here's a good explanation using the same methodology used in this thread. http://wahiduddin.net/race/dynotest.htm

Again, you are bringing in the technique and car control into the discussion. the discussion is ONLY about whether the rpm of the 996 engine is just "noise" and it is better to short shift or shift early.

I totally agree and advise the same techniques when going though, entering and exiting turns. we are ONLY talking about straight line acceleration here.

abolutely, during turns and traction, contol limited situatios in turns, it ABSOLUTELY depends on the drivers' and car's ability to choose the proper gear, regardless of engine potential.


Mark

Because you are not as silly as you seem to be here, im going to ask you politely. What are you talking about? why does exit speed of a turn determine or effect shift points down the following straight. what we probably have here is a falure to communicate.

Dave, listen closely. I said it once and Ill say it again. we are talking about maximizing acceleration at all points of a straight. meaning, taking full advantage of an engines potential, based on is HP curve. For this discussion, we are talking about a 996 engine.

The information was not found on the internet. Its a topic I have taught professionally for many years in a much more critical industry of applications relating to this topic. Also, I dont know if you have any engineering background, (actually , i know you dont) so, when you do, why don t you come back THEN and post like you know what you are talking about!

Now, as far as the LS1, Miata, ferrari, truck, jet, space rocket, all of these will have thrust curves that we can determine shift points or acceleration potential at any speed. Now, I never said redline all vehicles. In fact, i have a few pages with the 928 list, on shift points, some of which I brought up with you a year or two ago. It pays to know your engine and shift at points that Optimize power, not engine torque ! since you brought up an LS1, there are some that have rising hp curves that pay to shift at redline, but that redline is also a moving target, THATS why you need to know the curve and determine the shift points based on gearing. straight line acceleration ONLY Dave!!!

.

See what I mean, Viking? :banghead::banghead::banghead:









Professional Racing and Driving Coach

you have got to be kidding me, right? Ive said it litterally 1000s of times, but no one seems to listen. you shift at a point that maximizes HP. if HP is rising and then has a slight downward direction at near redline, then yes, you redline it to maximize HP available. there are some choked up V8s that have a big wide bell shaped HP curve before redline. THOSE pay to shift earlier.
SRF, LS1, LS7, 351 cleveland, Kawi Zr1, doesnt matter. you optimize HP to maximize acceleration.

Wow, you werent paying attention Bueller!! HP needs to be maximized. that will give you the maximum torque AT THE REAR WHEELS as multiplied through the gear box. Peak torque of the engine is often irrelevant. just look at the cup car. its peak torque can be anywhere. :) its shifted near redline.
Now, does that make sense. looking at power curves are just an easier way to determine shift points. it saves a step, thats all! (actually several steps)

Scott, you are on the same page as me. as you should be. Dave is a little lost when it comes to torque vs power. torque at the wheels, is determined by HP (or torque multiplie through the gear box at any given speed, which is obviously even harder to type as well as determine vs using HP values and curves)

Mark

I think you have it, and maybe have all along, but you know this is really about Dave. it seems he is the only one that doesnt understand. Unless I see something from him that shows he does get it, ill continue to try and correct his assumption that shifting before redline in a 996 street, cup or otherwise, is a bad idea on the straights.
I also have agreed and made the point clear, yet it keeps on getting brought up about shift points in critical areas around track. they are often not at redline do to the points you made in this comment of yours above. but on a straight,regardless of how you exit it. shif the engine at redline or at apoint that gives you the maximum HP. if the valves are floating and you get more hp than the next gear in a shift,well,then it pays to float ! :) (probably not though,but you have to look at the HP curve to determine that)


well, its not impossible to guess. LS1 powered street cars and many street conversions to race cars have .70 to .75 RPM drops (meaning the rpm is 75% of the pres shift RPM. even with a wide HP curve, which many V8s have, if the HP is climbing, then it pays to shift later,usually at redline. why do you think they limit redlines in race venues?


David, please! Let me understand the situation about coming off a curve, and how that would matter for a shift point following that curve, on the straight. at all times that you can, Im saying it pays to maximize acceleration by using all the available HP, regardless if you are coming off a turn or coming out of th pits , or out of a sand trap! if you want all the power, you run the engine in the max HP area, and often times, it is redline that allows you to do so.

Let me post 3 curves below. you tell me the shift points based on a 75% of the preshift rpm. (just using a ball park figure, but this is critical in reality)
(as a note, the 928 porsche has 70% of the preshift rpm as a drop for most of its gears)
996 GT3 cup car
Vet
928
ferrari
superchargedS2000 350hp
BMW M3 e36 euro
turbo s2000 with 500hp


anyone care to play?? anyone see the car that needs to shift short of redline?

:D

..http://www.hitjokes.com/pics/Humour/...on_For_Men.jpg

interesting curves on the SRF. If you notice , the HP curve is a belll shape from 4-6k. if the gear spacing is 70% as it is in my street car racer, or worse, the shift points could be 5600rpm as noted. I noticed he mentioned 3rd gear being 69mph at 5000rpm at 6000rpm its 82mph, so they are right on.

this article is exactly what we are talking about and is true and correct

Nice find

EDIT : notice that the SRF curve is almost idential to the 928 HP curve i posted above. even the gear ratios are the same. (near 70% delta). shift point? welll that would be before redline, for sure. :)

anyway, absolutely the right approach to determine shift points.

Now, if you remember, the original discussion was the 996 based on the torque and HP curves. it does pay to shift at redline, but for some unknown, proprietary reason, (VR Dave's secret sauce), he wont reveal why he thinks it doesnt. (ingorning anything other than straight line acceleration that is. No curve, traction limiting situations)

Dave Scott,

PE? is that your issue?

Anyone else notice that VR & MK's total post-counts are almost identical? 17,714 vs. 17,721?

Oh, and I would just like to correct one error... MK, space rockets don't have transmissions, so they don't need to shift gears at all. And they don't produce any torque either.

There, now everything is cleared up.

you think I or any top racer needs to have seat time in a particular car, to know when to shift it. now, you are the one that is joking. give a set of curves to D. Law or anyone else we see on the track and the shift points are obvious, to all except to you. So, when we race, you can short shift, stay away from the "noise" and Ill know a general idea of the 944's HP curve and shift accordingly. Then we will see who will have an advantage on the straights. :)

I know you have a short atttention span, so here is the net net

look at the HP curve, know the gear spacing and shift when you maximize HP.
(on all straights and when not traction or control limited)

period.

any comments??

Mk

I know what it is, you are still made you cant keep the car pointed the right direction when in a race! its all clear now.
those who can race, those who cant , teach.

It all makes sense!

Mk

Since you brought it up Dave, here are the Gear ratio comparisons of MM6 (base-model C5) vs C6)
Gear LS1/MM6 LS6/M12
1st Gear 2.66:1 2.97:1
2nd Gear 1.78:1 2.07:1
3rd Gear 1.30:1 1.43:1
4th Gear 1.00:1 1.00:1
5th Gear 0.74:1 0.84:1
6th Gear 0.50:1 0.56:1
Reverse 2.90:1 3.28:1
Axle Ratio varies 3.42:1
Final Drive Ratio varies 1.91:1

Here is the HP curve of a standard LS1

when would you guys shift this car from 3rd to 4th to 5th on a straight?

redline? something short of redline?

I dont know off hand, but looking at the dyno runs, it looks like redline to me.