RickBetterley

Where'd my thread go!?

mark kibort

It went by way of the same thing that happens when kids dont learn how to DO math in school, and just use calulators.

Anyway, back to your questions. Follow the HP curve and you will find your way.
plot the shift points of a post shift RPM to be 85% of the pre shift rpm. (cept for your 2nd and 3rd gear which is 80%).

Post some video at you most frequent track and we can see if if the gear set you currently use can be helped with a taller rear diff ratio, or if messing with the ratios would be a better choice.

Mark in Baltimore

Here we go...

bobt993

Mark, Rick has a 993 with a stock motor. And, so do I!! My car has been through a bunch of evolutions and both driver and car have fortunate enough to benefit from Pro driver instruction/setup. The result is the car has been a front runner in GTS3 with a couple of track records last year. I feel like I am trying to tell the dog next door to stop barking at midnight. Please do some due diligence and check your facts on data. Learn a little about long G accelerations and how they manage gearing on short boxes. I just did some looking on my office shelf and two very basic data books will point out how to calculate gearing based on data. While you are shifting to each gear you are certainly at less of a mech advantage, but the time lost in the power band of that gear has to be compared to the prior acceleration data before you decide to redline the prior gear. BTW stock 993 engines do not pull to redline. Rick I sent PM and will help anyway I can.

mark kibort

Bob, if you have data to support short shifting, your curve has to mimic the curve I posted above. Im not doubting the data, I just know how its calculated and where it comes from. I dont need to check my data, as there is no data to check. Im just telling you a factual analysis of where shift points will be. Again, if you had HP curves that rise and then flatten and then fall , if the next gear Hp is less than the HP at redline, it doesnt matter if the HP is falling, its better to shift at redline. this is VERY easy to visually see. if you have a stock 993, as you say, then this should be an easy analysis. you MUST have a HP curve like the one I posted last.

whether you look at overall thrust forces or HP curves, it doesnt matter. they will be exactly the same as far as the answer for determining shift points.

do a quick check of my math and logic here. look at your HP curves from the dyno. take the Redline RPM and multipy it by .85. (gear spacing for most of your gears based on Ricks gear spacing quotes). IF you see more HP post shift than priior shift, you are right, shift early.

It has nothing to do with understanding the "long G-acceelerations" you speak of. It has to do with putting down more hp over time or more torque to the rear wheels over time. this can be easily indicated by looking at the HP curve.
if you look at your hp curve, you can see what $100s of DAS systems will charge for (only in relation to this topic). You will not be disappointed by just trying to check it out. And if you understand the math, which is pretty simple you will get where Im coming from.

Give me the gear spacing, a hp curve and I can give you accurate shift points for optimal straight line speed 100% of the time. This will maximize your "long G-acclerations"
The noise that VR Dave speaks about when looking at falling torque curves is complete BS. As you say, as long as the HP pre shift is greater than what it will be post shift, you are maximizing acceleration . This is indesputable. But, im willing to listen if you dont agree. And boy, if Im wrong on this one, i SURE would like to know about it. Its like telling me the the earth doesnt spin.

mark kibort

Here are some graphs to chew on.


Down the page, there is a graph that is only in mph, but still at 127mph, X .85, gives you 107mph. ( this is the graph shown here) The post shift HP is greater, so this engine would need to be shifted earlier. The first few graphs on this thread, this is not the case. again, shifting before redline, is kind of the exception, rather than the norm for most race cars. stock engines, with a close ration gear box might show it to be a little more common.

The second graph is another stock 993, but a more peaky HP curve. it would pay for shifting at redline.

Its pretty handy to just look at a HP curve , apply your ratio spacing and know the shift points.

https://rennlist.com/forums/993-foru...aphs-here.html

Veloce Raptor

Bob, you clearly don't understand.

You (actually owning a 993 race car) know nothing. Mark (neither owning nor likely ever having driven a 993) knows EVERYTHING. And he will now make multiple gargantuan posts containing many superfluous graphs to prove it.

mark kibort

VR, again, mocking what YOU dont understand. Im just givng undeniable tools for determining shift points. It transends beyond any make and model of car, you knuckelhead! its physics 101. make fun all you want. call the HP past peak, "just noise" and mislead those who will listen to you. IM providiing solid, correct math based tools to determine shift points without the need of DAS. If you disagree VR Dave, why dont you give me an example of where this would not work, or STFU!

and yes, ive been on the track a few times in a 993.

by the way VR, didnt we go through this before with your incorrect assessement of the stock 996 shift points based on your "feel" of noise for the last 300rpm before redline, and then the curves proved you were wrong. along with a few other folks that got it. then, you backpedaled about "certain turns", control, traction", where that was clearly rulled out in the comparison. you are advocating shifting before redline and often times this can be a 10-30hp loss in accerative forces unless you know the HP curve (or set of torque curves) for that particular car. actuallly, when racing, i count on this kind of misinformation when facing cars with greater performance packages.

Mark

Bill Verburg

here's what your transmission looks like now

compare that to a Cup g50/30


You don't need to use every gear, having such short gears means shifting a lot more, sometimes at an inconvenient place

bobt993

Bill, nice to add in his gearing chart. Rick have you considered setting the car up for a 285 R6 with 245/40 up front. The 285 is a little taller. Set your max speed for that setup, chip the 993 and move your RPM limit up 200 rpms. Change the clutch setup to the Cup Car setup with the turbo pressure plate for a little quicker shifts. That helped me with corner exits and having a short box means your shifting quite often.

mark kibort

looks like if he just gears up the rear end, he could approximate the cup gears, and give himself a higher Max speed of near 160mph, without sacraficing much
looks like a 15% taller final drive would do it.

what do you mean, " dont need to use every gear" ? you mean skipping on downshifts? Im sure you can mean on upshfts.

mark kibort

so just go with the taller tire for the 2-3% higher top speed,and then another 2-3% of changing redline to 7000rpm? I guess that would be one way to do it , but only getting him to near 148mph. but if it is a street engine, sometimes the owners dont want to run them at high rpm's for extended periods of time. I think a taller rear end might help kill two birds with one stone. get the higher MPH and possibly pick up some more grunt out of the slower turns by being able to use 1st gear, which is currently not functionally fast enough.

Veloce Raptor

Whatever you need to tell yourself to sleep at night, gladiator boy.

You ever ask yourself why you got kicked off from RU recently?

I guess, like everyone else here, I am going to have to put you on Ignore. You schit on every thread it seems. You don't know what you're talking about. And you defend your abject ignorance with the militancy of a rabid squirrel.

I (like pretty much everyone else here) am done with you.

mark kibort

VR, you are a joker. Im only tryng to help those weed through the mystery of a pretty simple subject.

I dont know what Im taking about? really? isnt it funny, after all these years you have NEVER steped up and provided anything other than your seat of the pants proof for your points. Sorry VR, nice try.

all you have to do is provide one instance where my "not knowing what Im talking about" is wrong. It cant be wrong, because its simple math and a simple equation.

Im not talkng to you anyway, yet any post by you , instead of adding value is just an attack to make yourself feel better. Let Rick decide if what Ive posted hasnt helped. (or what Bill just posted hasnt helped) you are arguing against simple fact and cant even make a comback that defends your assumptions. seat of the pants feel, with "noise" for fallig HP typifies your advice. I hope I have a chance to race someone you have coached !

have a good one beach boy!

PS : racer university..... good intentions, good ideas, but a waste of time, based on no freedom of speach. I was on a trial membership and you got it, Scott has to chim in and argue with me about weight transfer for g-loading, being the same of two idential cars one being heavier. I said it was differnet, provided the equations to make the point to the original question. Same players, not tryng to find the truth, but trying to win arguments. Thats ok, Im sure they will be just fine without me. Mark can have his little good old boys club. Without being challenged, you dont improve. it goes for your mind too! So, pay money for the same thing we got going here? I dont think so.

anyway, re-read your interjections and then read mine. who is trying to create a discussion to help and who is just stroking himself?

mark kibort

Dave Scott,

Here are all your posts. Did you add one bit of value intead of starting an agument. I'm flattered you need to spend so much time trying to put me down to validate your measly existance here. VR, if you object to what Im saying, here is a tip, try and prove me wrong technically and Ill never post again!