Hi,

it was a very heated up discussion on a racing forum (now closed) regarding this subject so I was quite interested to check here, a bit away from that group of people what is the common opinion about this.

All my life I was told and used an upshift method trying to move shifting points in the way so each new gear would start slightly after RPMs of a max torque and prolong into the area of a max HP. With p-car I have now I have max torque at 4500 and max HP at 6800 with is almost like ideal 2K rpm section for upshifts, usually goes like 4.7K - 7K for 1-2-3 and a bit below like 4.5K - 6.5K for 3-4-5.

Surprisingly for me apparently there are different concepts regarding this method apparently, so I would be very curious to hear about it if such different methods do exist - what are they and what is the rational behind it?

essentially it all comes to a question - say, if your max torque is way low (like 4K) and max HP is way high - say 8K RPM - how do you upshift 1-2-3-4-5 gears sequence?

 

It depends. THAT'S why you will get so many opinions.

 

I assume you're talking about on-track shifting for maximum performance...?

 

On the track... redline.

 

If your goal is maximum speed, you should upshift at redline. Your goal is maximum torque at the wheels, not in the engine.

This does not "depend". I don't believe there exists any street car where the optimum shift point is not red line, you would have to have a very strange gearing (not much difference in ratio between gears) and a very strange engine (very low power at high RPM) for that not to be true.

 

I basically agree with your comments but there are cars that don't gain much if any benefit from being revved to redline. The VW/Audi 2.0L TDI, for example makes maximum HP of 140@4200rpm with a redline of 5000. But it doesn't do anything with those final 800 revs and it's torque curve is so broad that there's no need to wind it up to keep the next gear in the power band. I don't have another example off the top of my head, but I know I've seen magazine tests where similar situations exist, usually with lower performance economy cars.

Not to quibble too much with your point; it is generally correct in my experience.

 

There are two ways to look at it. One is to shift when the torque at the wheels in the next gear would be better than in the current gear. "torque at the wheels" = engine torque * drive ratio. A simpler way is simply to say you want to maximize horsepower, so you shift when the horsepower in the next gear (after rev drop) is greater. It should be obvious that these two ways are equivalent, because horsepower = torque * rpm and rpm is just drive ratio / vehicle speed.

See for example :

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

http://www.digitalcorvettes.com/foru...ad.php?t=69986

https://rennlist.com/forums/996-gt2-...ft-points.html

 

The characteristics of the engine and it's ability to rev freely are part of the equation too. It's possible in theory that torque at the wheels is greater the higher the rpm, but if it takes too long to extract that extra power by revving an engine that isn't happy doing it, you will have lost more time than if you upshifted into a range where the engine is more comfortable making power. My example above was of a turbodiesel engine. I think most diesel owners will tell you that winding them to redline is not the best way to achieve max performance.

BMW's 335d has a redline of 5000rpm but the automatic transmission won't shift above 4600, even in manual mode. Maybe BMW knows something.

 

The question applies to 997s, not other cars... And the answer for track shifting is redline.

 

All due respect, Tony, but I know that. I was simply responding to cbzzoom's comment in post #5 that "I don't believe there exists any street car where the optimum shift point is not red line". I believe there are. Other than that, I think we're in agreement.

 

OK. That's true for other less performing cars with less linear power curves but for the OP, it's redline, that's what I meant.

 

I looked at the power curve of the VW TDI you mentioned, and it looks like proper shift point is very close to red line, maybe just barely under, it depends on how flat the gear ratios are.

Many people shift too early because they are trying to put the engine in its "power band" where torque is maximum and the car feels like it's making good power. That's wrong.

 

I have driven a VW TDI in Germany for several years. I often drove at high speeds ( up to 125 mph) and I can tell you that shifting at redline does not produce the fastest acceleration. After about 3500 to 4000 rpm the engine just makes more noise.... not more power. The best power came from 1800 to 3500rpm.

 

I don't want to take things off track but I'm having trouble seeing the arguments for any answer other than redline. And wouldn't Porsche optimize things so that a properly quick shift at redline will place you in an ideal (or nearly ideal) RPM point in the next gear?

 

Exactly.

For Porsches absolutely, and most other cars for that matter, but as we've been discussing there are some exceptions. The TDI is an example; maximum HP at 4K, with a broad torque band low in the rev range. There is simply no point in revving the last 1000rpm to to the 5K redline; the car will be slower than if you shifted earlier, just as Fahrer's experience attests. We have an A3 TDI on order and I've had some experience driving with that engine. Fahrer is correct.