Power de-tuning - limiter or remove parts?

[Broseph]

What is your method for de-tuning the power of a car to hit a PP limit? Do you remove parts first, then use the limiter if needed, or do you use the limiter as much as possible then remove parts if needed?

I ask this because of what this does to the power band of the car in the process.

Just removing parts to get to a PP limit will end with a higher max HP rating at the target PP, but you will have the standard HP "peak"... but if you use the limiter to lower power, you get a flat power curve that puts you at max HP through a wide RPM range, but that max HP is lower at the same PP limit.

For instance, take this Celica GT4.

First, I have removed all of the power increasing parts (turbo, exhaust, intake, chip, etc.) and left the power limiter at 100%. This leaves us at 464 PP with max hp of 302 at 6300 RPM and a max torque of 257 at 4300 PRM. The horsepower has a short peak time, while the torque has a long plateau.

Now, if I leave all of the power increasing parts on, and instead use just the engine limiter to lower power until I hit that same 464 PP mark, it leaves us max hp of 281 at 6300 RPM and a max torque of 339 at 4300 RPM.

With this method, you hit the maximum horsepower very early and stay at max all the way to redline. Would this be a better option for downtuning a motor as it lets you be at max power throughout pretty much the entire power band? Or is it better to remove parts instead and leave the car with a more "traditional" power curve?

 

[Broseph]

EDIT: I'm guessing the first method would be better for high speed courses, and the latter would be better for twisty/technical courses?

 

[VTiRoj]

The best way to find out which is better would be to have a drag race and a few time trials on different types of tracks and see which one comes out faster. At least then you'd have proof as to which method is best.

 

[rosckolove]

I know this.

Usually PP races are only held in random lobbies. Random lobbies usually run small length races with a standing grid start. Holeshots/Launch can be important depending on the strength of your competition.

The car with more torque, will allow you to make your first gear taller allowing you to stay in it longer while the other guy inevitably shifts sooner and drops back. Also allowing for slightly closer gear spacing. This also applies in coming out of hairpins. The car with more torque can stay in a higher/taller gear because he gets power from a lower rpm range.

I think drag racing them is all you would need to do. Running circuits would take a lot of time and adds a lot of variables in consistency and in tuning the trans.

Horsepower is speed, torque is how fast you reach that speed.

I'm not sure how well torque curves are actually portrayed when in the car racing at speed, I don't notice much.


This I don't know, its just my opinion.

I would choose torque, its what moves the car, and I think its the better option.
Edit- As in the option with the parts installed and power limited.

Depending on power curves or maybe low HP cars there lies some exceptions.

 

[esoxhntr]

in a PP limited room, for most cars and tracks, removing parts (with maybe 1-3% engine limiter on cars that have a really peaky power curve) is the way to go.

In a HP limited room, using the engine limiter is the way to go

remember, hp = (torque * rpm) / 5252

therefore, torque = (hp / rpm) * 5252

plug in the numbers from your examples and see how much torque you make at a given rpm. your 'flattened', lower HP curve actually makes less torque at peak too.

edit i'll do it

ex1. (302 / 6300) * 5252 = 251.76 lb/ft at 6300

ex2. (281 / 6300) * 5252 = 234.25 lb/ft at 6300

sure ex2 makes more peak torque.. but racing is done around peak power not peak torque.

ex1 has a nice flat torque curve from peak torque to peak hp.

ex2 torque falls off DRASTICALLY past peak torque. assuming the drop is linear you could plot a straight line from 339@4300 to 234@6300 and figure out where you are at torque wise in between.

hope it makes sense

 

[Johnnypenso]

in a PP limited room, for most cars and tracks, removing parts (with maybe 1-3% engine limiter) is the way to go.

In a HP limited room, using the engine limiter is the way to go

That would be my general rule of thumb also but I think you can use much more power limiter without a serious effect on HP. 10-15% only costs you a couple of HP relative to removing parts and will have no effect on lap times, if you are starting at 100% to begin with. It's the bigger uses of engine limiter like 25+% that really rob you of significant HP.

I have never paid much attention to the torque curve. When circuit racing 95%of the time you are at or near the redline, so the torque available halfway up the rev limiter is meaningless at that point. At high speeds, HP is king and I think you are better off using a little engine limiter to flatten out the power curve of some of the peaky cars, while giving up peak HP in the process.

 

[carracerptp]

Depends on the car. If you look at the top guys tunes on a time trial they use the power limiter. It's all a balance. I try and uses as much power limiter as I can with the gear ratio.

 

[Motor City Hami]

I remember back to the beginning of GT5 it seemed that the belief was to add all of the engine parts then use the power limiter to it's fullest. The flat HP curve with seemingly no affect on torque was thought desireable.

Now I think the GT Planet community is divided on the subject. I see tunes using both methods.

With the availability of the straight line test track, it is really easy to test for yourself. The back to back testing that I have done between power and torque brought back power as the winner all of the time.

I like to use very little power limiting. The first parts that I add are:
1. Racing Exhaust.
2. ECU or Engine Tuning, if I don't think I'll need to remove it later
3. Intake and Exhaust Manifolds
4. Cat
5. Air
6. Turbos

I would bet that the drag racing community has spent the most time testing this. Would be interesting to hear from the.

 

[CSLACR]

I'll be the first to tell you the drag strip is a great spot for testing.

I'll be the last to tell you to test hp curves for road racing on the drag strip.

Drag strip = prime gear spots, 100% of the time.
Road course = pulling from lower RPM than you should hit on a strip.


To answer the OP, 4-8% is usually best, though there are a million factors, and therefore no true "answer".