raise rev limiter/shift point on 986 Boxster?

[Jake Raby]

Turbo M96 engines can be real powerhouses when the engine is stripped and prepped for forced induction. I have yet to have anyone pull the trigger on one of these engines that is ultimately prepped and coupled to an application specific, top of the line turbo system.

Otherwise, you have a grenade with the pin pulled. Instead of "forced induction" its more like "forced failure".

[JTP]

Originally Posted by Jake Raby

Turbo M96 engines can be real powerhouses when the engine is stripped and prepped for forced induction. I have yet to have anyone pull the trigger on one of these engines that is ultimately prepped and coupled to an application specific, top of the line turbo system.

Otherwise, you have a grenade with the pin pulled. Instead of "forced induction" its more like "forced failure".

Jake, what kind of power would your turbo setup produce and how much would it cost as a fully installed system?

[thstone]

Blue2000s, I don't think that this is going to work out as you expect...

As you can see from your plot of Wheel Torque vs Road Speed, 4th gear torque peaks and is going down as the engine reaches the max rpm. It happens to reach max rpm just as it is about to cross below the 5th gear curve. If you extend the redline (increase the max rpm), all you're going to do is extend the 4th gear curve below the 5th gear curve. Which says that you should have shifted.

And in fact, you really should have shifted when the rear wheel torque peaked instead of riding out the decline as it is more beneficial to be on the increasing side of the torque curve than on the decreasing side.

Look at it this way, a CVT transmission does not simply run the engine at max rpm, instead it runs the engine up through the maximum torque.

[blue2000s]

Originally Posted by thstone

Blue2000s, I don't think that this is going to work out as you expect...

As you can see from your plot of Wheel Torque vs Road Speed, 4th gear torque peaks and is going down as the engine reaches the max rpm. It happens to reach max rpm just as it is about to cross below the 5th gear curve. If you extend the redline (increase the max rpm), all you're going to do is extend the 4th gear curve below the 5th gear curve. Which says that you should have shifted.

And in fact, you really should have shifted when the rear wheel torque peaked instead of riding out the decline as it is more beneficial to be on the increasing side of the torque curve than on the decreasing side.

Look at it this way, a CVT transmission does not simply run the engine at max rpm, instead it runs the engine up through the maximum torque.

You stay in the gear that gives you the most torque. Whether it's on the increasing or decreasing side of the slope doesn't matter. If you shift out of a gear to the next and drop in wheel torque more than you would have by staying in gear, you loose acceleration. No way around it.

For max acceleration, a CVT keeps the engine around peak torque and alters the gear ratio to match road speed, which is the way to keep the most torque to the wheels.

You're right about 4th gear in that at redline, it's just crossing 5th gear torque. There's a slight benefit to shifting before redline in 4th. I doubt anyone could hit that exactly right. If the OP just increased redline without altering the engine torque curve, there would be no acceleration benefit in the higher gears, but there would still be benefit in the lower gears. If you alter the torque curve, everything could change.