Veloce Raptor

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

SundayDriver

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.

JustinL

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

mark kibort

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

mark kibort

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!!!

.

Veloce Raptor

See what I mean, Viking?









Professional Racing and Driving Coach

mark kibort

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

mark kibort

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?

Veloce Raptor

..

mark kibort

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)

mark kibort

Dave Scott,

PE? is that your issue?

quickxotica

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.

mark kibort

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

mark kibort

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

mark kibort

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.