mark kibort

Transmission ratios: Manual
1st gear 3.91
2nd gear 2.32
3rd gear 1.61
4th gear 1.28
5th gear 1.08
6th gear 0.88

percent of redline RPM after a shift
59% for 1-2nd gear
69% for 2nd to 3rd gear
80% for 3rd to 4th
83% for 4th to 5th

You can clearly see from the graph , and i used 2 gear shifts, that shifting at 7500rpm yields the best average HP and maximizes acceleration in ANY gear shift for all gears and speeds.

Below, ive added a C2S dyno run with the torque curve shown.. you can see it clearly falling dramatically after 6500rpm, but that doesnt matter! its all about HP for shift points OR.......... you can find the programs and applications and arrive at the same result

ProCoach

Mark, the torque curve is important, maybe even MORE important. So without it, it's not the same as your graph with your notes on it.

Apples to oranges.

cello

Deja-vu all over again, lol

mark kibort

Peter, the torque curve is not more important.. it cant be.. torque and HP are intrinsically tied together, PERFECTLY. HP just has more info associated with it.

It's not apples and oranges. by "law" HP determines acceleration or force at any speed and Ive described why many many times here. so, because of this, whether you use HP or all the calculations of torque, gear ratios, tire diameters, the answer and result is exactly the same!

So yes, the thrust curve will be in exact proportions as the HP curve will be at any vehicle speed. Trust me on this one. it's simple physics..... and a challenge to you if you doubt it... find one condition with the HP and torque curve where this isn't true and doesn't point to the exact same results as a thrust curve would.

Led Zep said it best........The song remains the same.

ProCoach

Manifold

I've tracked a 997.1 C2S. I didn't study data to optimize shift points, but shifting near redline seemed to work best for all upshifts. Probably not much time lost if you shift a little below redline. The gearing seems to be matched well with the engine.

mark kibort

Yep. you seem to understand it. for every little bit you shift under redline, you follow the HP curve down on the resultant shift power available. so you do lose some, but its an average too. the 997 transmission is still not perfect, and couldnt be unless it kept the engine at or near max HP , which it does a great job with from 4th on to 6th, but not perfect. perfect would be to keep the engine at that little table top of power from 6500rpm to 7000rpm

If you think about it. if you short shift just 200rpm shy of redlne, you lose about 10hp on the post shift, for how ever long it takes to make up that 100 or so RPM . so when you are in that next gear you are down 3% on power and accelerating force, (contrary what Peter said, 3% down on power is the same as 3% down on rear wheel forces at any same speed) but its only for a short time, the delta gets greater as you spend more and more time in the next gear at higher speeds. That's why the gears are closer together at the higher speeds vs the lower speeds. (i.e. 1-2 vs 3-4-5) it matters more at the higher speeds!

mark kibort

Just for information here. you made a statement and didnt back it up with anything. I think I posted all the reasons/data and math to show how simply you can find shift points for any car with a HP curve and RPM drops per gear. It might be sometimes hard to follow if you dont use the math on a regular basis

Since this is your business..... i would be very interested in your explanation of how it is possible , or from what perspective, that the torque curve is more important, or how a comparison is "apples to oranges" ,or what that analogy means.

I think a better analogy is power to amps or power to volts.
but, if we are talking about doing work, or ability to effect the rate of KE change, do we care if it's more amps than volts or more volts than amps?
with power, do we care if the torque is high or low if the power is the same? maybe for component strength ratings, but not on its effect on accelerating a mass (car) . Again, power is a cars capacity to accelerate at any speed, just like energy is a bodies ability to do work.

again the law and simple identity: acceleration = power/(mass x velocity)

Thundermoose

Torque = HP x 5252 / RPM so easy to calculate torque curves if you have HP plotted against RPM.

This is a tastes great less filling debate.

Mark and I are in the HP is what matters camp (as long as it's climbing even if torque is falling slightly) as the gearbox is a torque multiplier and a lower gear will almost always apply more torque to the wheels than a higher gear.

Since most of our cars make increasing power to redline there is no good reason to short shift (at least in straight line).

Having seen this debate on multiple forums I have never seen anyone move from one side of this argument to the other based on math, experience or rhetoric.

I say we agree to disagree. I'll try to shift at redline and others can shift wherever their torque curve tells them.

Matt Romanowski

Here is another opinion by some smart folks https://www.hpacademy.com/technical-...ractive-force/

ProCoach

Mark, your 928 and DynoJet (M3?) graphs show the HP and torque curves. The 997S does not. That is what I meant when I said apples to oranges. Add the curve to the 997S so we can see it.

This is the graph the Shift RPM app makes with the proper information inputted.

https://www.hpacademy.com/assets/Upl...leTQ-Ideal.jpg

mark kibort

It's really not a "less filling , taste great" discussion. you either get it or you dont. (and there are some that finally get it by the way after seeing the facts)

And, Illl add something to your point... the HP curve doesnt ahve to keep rising.. it can in fact, be falling too. the answer to the shift question is, if the engine makes more power at redline than it does post shift, leave it in gear and redline it......... it's that simple. its the area under teh HP curve we care about and that will yeild the most rear wheel force (wheel torque) at that speed possible by the car, its engine and its transmission. so, most cars have a falling HP too, but it still pays to redline because the post shift HP is still less than redline HP, bringing the average up by redlining. its all about maximizing HP or rear wheel forces. (not engine torque, but REAR wheel torque which are grossly different)

i gave a very clear example of when it pays to short shift. the HP cuve has to be falling so far and so fast that the next gear has more power before redline. THEN and only then, does it pay to shift or be in the next gear.

There are so many that are thinking , "im going to put a lower gear in my car to get more acceleration and get in the torque range of the engine.. when actuallty, the flat HP curve makes it a non issue. if you ever are in the max HP range, the torque is falling at a 45 degree angle! yet you still shift at redline... why is that? because if you work out the simple math, you will see that acceleration forces when ever you are at max or the same hp at any speed, will be identical!

good article, but the HP curves point to some short shifting to optimize HP. (like the graph i posted which is very rare ) but , i do like the summary and the fact that HP determines acceleration forces. engine torque does too.. its just harder to extract because you need to plug in more variables (i.e. gearing , tire diameter, etc) with hp, it has all the info you need for shift points, sans the RPM drop %. so, you need no calculators, programs, etc, other than your eyeballs to see if the HP is greater or lower at redline, requiring a short shift or not.

mark kibort

Peter, i had the second graph added to the next post. maybe you didnt see it. here it is again with the same superimposed shift points . again, you dont need to look at the torque, as it doesn't really matter if you have the gear spacing. if you had only torque, you would never know shift points unless you had gear ratios and multiplied out the rear wheel forces... HP does this for you , because HP is proportional to rear wheel forces at any vehicle speed.

Here is the original post with both the 997 curves one without the torque curve.

https://rennlist.com/forums/racing-a...l#post13852597

so here is the OP 997C2S HP and torque graph with two shift points for an example

morsini

Deja-vu, deja-vu, deja-vu, all over again. FIFY

Gofishracing

01/02/2017. Full throttle..