Hey guys so Ive been having a strange boost issue since I got the car. It is a 91 s5 turbo with 3" turbo back exhaust and thats really it motor wise. I have an aftermarket boost gauge. So when i floor it it spools up normal and hit about 10-12psi. However once i get to higher rpm around 5000ish boost will start to drop to anywhere between 3-5psi. There is no leaking air noise and nothing really changes a lot besides feeling that the car is pulling slightly less hard. Has anyone heard of this happening before? I will be making a pressure tester this week to check. Just wanted to see if you guys had any input.

 

If your boost reaches over 10 and then drops it's likely caused by the ECU which is cutting the boost to prevent from overboosting. Stock engines usually should run under 10 psi or so if that.

 

https://www.rx7club.com/2nd-generati...h-rpms-897247/

https://www.rx7club.com/2nd-generati...op-off-761771/

 

Ah I wasnt sure since I read about fuel cut, but did not know the ecu would just cut boost instead of fuel. So basically I just need to port my wastegate correct?

 

The stock wastegate is only 5.5psi on the S5 just like the S4. Except the ecu has a boost duty solenoid it uses to allow boost pressure to be raised to 8.5-9psi.

Side note, I wasn't aware there were other Tii's running around locally.