Gruppe N tune.

Hello guys.

My name is Christos, and I have a small "issue" if we can name it like that , if someone have experienced the same problem before.

I have tuned a gruppe N rally car with some good results on E85 fuel and really safe tune. (see dyno sheet)

The "issue" i see on this is that we loose REALLY quick boost at higher RPM.

We have 302kpa(2.0bar) at 3500rpm with 0.84lambda and 9 degrees of advance timing.

The boost is falling really quick as i have 250kpa (1.5bar) at 4500rpm with 0.79lambda and 10 timing advance.

The car is a Evo 9 mivec engine with standart OEM engine and turbo BUT with a 33mm restrictor.

The boost is NOT driven through the ECU , The solenoid it is not on the engine , the wastegate works by it self mecanical , it just have been tighten at its max.

I have no boost leaks or something like that it just wont keep the boost more rpm that it already does.

But the car is really not fun at all to drive as it has a good power only from 3500rpm to 4500rpm :/

What Lambda do you suggest to keep on this one regarding that the pressure it is high for a rally car,

this car is droven flat out all the way on the "track"

I can also upload the log of the dyno plot if it needed to someone.

Regards Chris.

What you'll likely find is that the turbo is over speeding, which is not only dangerous for the turbo bearings but also the engine.

Reduce the mechanical load on the turbo and use either the ECU or standalone boost control to slow the turbo at higher RPM and you'll likely find that you'll generate more boost. This comes down to the efficiency range of the turbo, it sounds like you are going way beyond that.

Hello chris thx for the reply.

so your saying that if i slow down the spoop speed of the turbo i will generate more Bar at higher rpm?

I will try to reduce the mechanical charge of the wastegate , and isntall a solenoid to try keep more boost on higher rpms.

The turbo restrictor you think it does nothing to the turbo airflow at higher rpm ?

The turbo restrictor has a massive impact on the efficiency range of the turbo.

The idea of the restrictor is to limit your power by restricting the flow of air into the engine, you can see this from your torque levels dropping and the BHP staying almost level across the RPM range.

What you are seeing in terms of boost curve is to be expected with a restrictor. The restrictor really limits how much air the turbo can suck in at higher rpm and it's not possible (or beneficial) to hold the boost flat. I often find that the engine will make more power at high rpm with less boost, so don't fall into the trap of believing that more boost is always better.

besides, i would be scared to put so much torque to the OEM rods!