Something is up with my internal wastegate. When I turn up the boost to 11 psi, it holds boost very well with no signs of fluctuation. As I turn up the boost, say to 13 psi, it will boost that amount from 4000-6500 rpm, but settles back down to 11 psi. It seems like the internal wastegate is preventing me from going higher than 11 psi. Any ideas?

 

What is your exhaust setup like? Maybe your exhaust is getting backed up at the higher rpms, causing the reduction in boost.

-deepsi

 

i doubt that i have full 3 inch exhaust system

 

Alright, so that is not the problem

 

Not to ask a silly question, but can your turbo physically pump out more boost at that RPM?

Case in point: my van's stock Mitsu 13c turbo was horribly undersized for my 2.5L engine, nevertheless I kept upping the boost until, finally, I was running with the wastegate actuator vacuum line unplugged. (Day in, day out.) At a full throttle launch, the boost would quickly rocket to 17 psi by 2500 RPM and then level off... until I hit 4800 RPM, where the boost level would begin to drop, and drop, and drop... by 6000 (my redline) I would have only 14 psi. The wastegate was closed solid (I had even shimmed the actuator to ensure this) but the tiny little turbine was literally maxed out and was physically choking the engine (there was very noticeable power loss at 5000+ RPM). I have no idea what turbo you're using, or how your compressor's flow map matches your car's volumetric efficiency, your intercooler, etc--this is just another idea.

BTW: testing your exhaust is easy: just drop the pipe off the turbo and go for a quick drive. You'll spend no money doing it and then you'll know for sure.