Getting an engine ready for a horsepower restricted race

[Alex Mart]

It is so great that sport mode in GT7 allows tuning for some events, some of us can now practice tuning for competitive racing.
Building up my car for the Daily at Deep Forest a question dawned on me though. That race is power restricted at like 295HP so is it best to max out the engine upgrades and then tune down the engine power with the power restrictor/car computer OR only install the mods necessary to meet the horsepower regulations?

I have only try installing the necessary mods to reach max power allowed out of my car mainly to save some money while i grind in single player modes, so i don't know how the car handles with max upgrades and power restrictor detuning, but if i had to guess i would say it's better not detuning the engine to use the most its capabilities instead of "keeping it on a leash".

Can someone list the pros and cons maybe?
Thank you

 

[sumbrownkid]

I saw SuperGT do the daily race you want to do and put the highest spec parts then used the power restrictor to get the car to the stated limit.

The only pro I can see for this is that the higher spec parts have inherent benefits that don’t necessarily show up as raw power. As for cons, it’s pricey.

 

[sysasysa]

Also about detuning, is it better to lose HP by limiting the ECU or using a restrictor? Or does it matter at all?

 

[frenchfries]

I'm experimenting with my VW GTI right now:

ECU:
This can get me precisely to the HP limit. But it lowers the max torque more.
Max HP: 295
Max Torque: 336

Restrictor:
This is more imprecise than the ECU, but maintains torque more.
Max HP: 293
Max Torque: 338.4

Haven't turned any laps to see if there's a difference in practice between these settings.

In general, since only Max HP is restricted, perhaps the engine could be tuned to maximize torque, or provide more HP along the RPM range where HP isn't at max?

Edit: Interesting to note, using the ECU to tune doesn't change the torque or hp graph shapes at all, while using a restrictor does.

 

[Keef]

You'll need various combinations of parts and restriction to get the best power and torque saturation throughout the powerband.

For example, as a general rule, it appears that the intake restrictor reduces high-rpm power first which makes sense. That helps preserve low-end torque. But if you restrict with the ECU, that reduces power across the entire powerband at the same ratio which means you're also driving down your torque numbers - it doesn't actually change the shape of the powerband.

So for example, putting any aftermarket turbos on the R32 GT-R and then detuning it actually results in less torque than standard. In general, if a car already has more power than necessary, it's best simply to restrict it than to build first and then restrict. Most street cars already have broad powerbands anyway so restricting it without tuning it helps preserve drivability and torque.

 

[Alex Mart]

You'll need various combinations of parts and restriction to get the best power and torque saturation throughout the powerband.

For example, as a general rule, it appears that the intake restrictor reduces high-rpm power first which makes sense. That helps preserve low-end torque. But if you restrict with the ECU, that reduces power across the entire powerband at the same ratio which means you're also driving down your torque numbers - it doesn't actually change the shape of the powerband.

So for example, putting any aftermarket turbos on the R32 GT-R and then detuning it actually results in less torque than standard. In general, if a car already has more power than necessary, it's best simply to restrict it than to build first and then restrict. Most street cars already have broad powerbands anyway so restricting it without tuning it helps preserve drivability and torque.

So to some extent restricting power is not the solution because you’ll have undesirable drawbacks?

 

[Keef]

So to some extent restricting power is not the solution because you’ll have undesirable drawbacks?

True, which is why I mentioned the difference between ECU restriction and the intake air restrictor. But for the most part, cars with enough chassis performance to do well in Race B or races like it (R34, R8, GT3) all have more power than the limit and need to be restricted anyway. In that case, the intake air restrictor usually results in a broader torque curve than the ECU restrictor.

 

[wyans_]

Also about detuning, is it better to lose HP by limiting the ECU or using a restrictor? Or does it matter at all?

Always use the restrictor first, then the ECU output. The restrictor limits airflow, so at lower engine speeds, you still get full use of all the other engine upgrades. When you use the ECU output, you're removing energy output across the whole RPM range. The difference in torque for tuning for Daily Race B using only the ECU output and only the Restrictor can be around 100 lb-ft, which is astronomical.

 

[SnuggleMaster]

My understanding is something like engine balancing will give you a higher redline. Is this not desirable?

 

[Harmonic]

In general, if a car already has more power than necessary, it's best simply to restrict it than to build first and then restrict. Most street cars already have broad powerbands anyway so restricting it without tuning it helps preserve drivability and torque.

I don't agree with this. Adding aftermarket engine parts makes it so you can set the restrictor lower to meet the event restrictions, and that often means you get a flatter power band. In just about every car I've tuned so far, it has benefited from using certain upgrades and restricting it more rather than just restricting it in stock form.