How to limit horsepower for NASA racing

[jkittleson]

Anyone have thoughts on how to reduce horsepower on an engine? The car is 2006 Corvette with E38.

I am going to run NASA ST1 next year and it requires a HP to weight ratio. My 427 makes 576 RWHP and I need to trim it down to around 520.

I have a GM Stage 3 cam in it now, but also have a Katech Torquer that I could stick in it. I would probably make around 550 RWHP in that setup. Wonder if I should stick with the Stage 3 cam, or use the Katech cam "I will lose power up top", then try and reduce the power with throttle opening?

Any thoughts would be appreciated. I've never tried to lose power before.

[mecanicman]

For what you want to do, the power under the curve is important. Run which ever cam will give you more. A throttle restrictor will also negatively effect this, I would not do this unless absolutely necessary. My solution would be tuning the engine on the dyno, just pulling the timing out in the required areas. Normally we adjust to reach a peak horsepower number. Its not uncommon to pick up 50+ horsepower on a modified engine setting the tune up right, you just need to dial it back. My 2 cents worth...

[Nick 2K2 SS]

At what RPM does the car make above the power to weight ratio? Remember HP is a function of Torque X RPM so if you can limit your RPM with a lower rev limiter then maybe you would keep it below the HP:Weight ratio required. This way you wouldn't lose any torque for coming out of the turns with. You would just need to shift more often maybe.
Otherwise I would probably back timing off along with maybe a more restrictive exhaust or intake.

[DSteck]

Just pull timing extremely aggressive at the point where you start making full power. The Katech Torquer might work out better for you, ultimately.

[Chris@HPTuners]

Also, there is a maximum throttle value that can easily limit the WOT throttle %. This will obviously effect your low down power so maybe just pulling a little timing where you want it will be best.

[jkittleson]

Thanks for replies. I appreciate the advice.

I'll try the Torquer cam and pull some timing.

Any adverse effects from just pulling timing? Can you really tune out 50 - 75 HP by just pulling timing?

[IDRIVEAG8GT]

Thanks for replies. I appreciate the advice.

I'll try the Torquer cam and pull some timing.

Any adverse effects from just pulling timing? Can you really tune out 50 - 75 HP by just pulling timing?

Damn straight! The ECM has a capability of going -64 so you could probably drop more ponies than that.

[eficalibrator]

I'd be REALLY careful about using only timing to limit the power. Retarding the timing puts a lot of heat into the exhaust (valves, headers, etc...) and can be a real problem in a road racing application where you're going to spend some quality time near that point. You don't want to use just a rev limit either since that clips the speed you can hold a certain gear to, and may force a shift at an inopportune time right before a corner when racing.

The best solution is to do it with airflow limiting. Check the NASA CCR for that particular class. I know that in AI, you're not allowed to use the ETC for power limiting to satisfy the RWHP/lb requirement, so it might not be kosher in your class either. The best solution in that case is to restrict the inlet with either an orifice plate or undersized filter inlet that doesn't shroud the MAF sensor.

[jkittleson]

I'd be REALLY careful about using only timing to limit the power. Retarding the timing puts a lot of heat into the exhaust (valves, headers, etc...) and can be a real problem in a road racing application where you're going to spend some quality time near that point. You don't want to use just a rev limit either since that clips the speed you can hold a certain gear to, and may force a shift at an inopportune time right before a corner when racing.

The best solution is to do it with airflow limiting. Check the NASA CCR for that particular class. I know that in AI, you're not allowed to use the ETC for power limiting to satisfy the RWHP/lb requirement, so it might not be kosher in your class either. The best solution in that case is to restrict the inlet with either an orifice plate or undersized filter inlet that doesn't shroud the MAF sensor.

Thanks EFI. I believe I can use the ETC for limiting in that class. Just as long as it makes the required HP I should be in good shape.

Wonder if I could run my killer bee air cleaner inside of a sealed airbox, then play with the inlet side there as not to disturb the MAF.

[LSX378]

Enable TCS method via ETC only and then use the max torque rpm vs gear table.

The ETC will then limit the torque to your max values. It works here .