Brinkley

sh*T That didn't do it.

Sh*t it did do it!

Bonster

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

Werkstatt

"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.

J richard

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

garrett376

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!

mark kibort

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!

333pg333

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.

Bonster

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. You guys be good and don't get caught if you're REALLY good. Lol.

333pg333

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....

mark kibort

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.

mark kibort

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

333pg333

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.

onefastviking

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.

onefastviking

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 .......

winders

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