Just wondering if this is normal.

My car has a ported wastegate on a S5 turbo w/ 2.5 DP to Presilencer to CS 3inch single catback.

I have a MBC set to 9psi.
Lately the turbo will not hold 9psi at all in the upper rpm ranges.

It will jump right up to 9psi around 3.5k rpm but will quickly fall to 5/6psi over 5k rpm.

This is 1-3rd gear. 4th and 5th hold the psi fine.

I have noticed that I'm running richer than usually. Could the excess gas becausing power loss up top and the inability to maintain boost?

 

Check the spring tension on the BOV. If it is to weak you may be building alot of boost causing it to open slightly, resulting in a leak. Do not know how fast you are going in 4th and 5th but thoughs gears should be pushing alot of load building high boost.

 

Lower boost in the lower gears (especially in 1st and 2nd) is normal.
The engine / turbo isn't loaded enough in those gears, and the turbo needs the load to produce boost.

MBC's suck for this kinda boost control.


-Ted

 

our stock turbos do trail off boost late in the rpm range.

 

Hmm I think it may be something else like excess fuel.

I'm running rich and I use to be able to boost to 9psi.

I'll check my bov tension. I did make it extremely loose.

 

I doubt it's your bov spring set too loose. If it was too loose it would be leaking at idle. Boost doesnt push the valve open, it's vac that does. Easy way to test is to pull the vac line off your BOV and see if the problem goes away or not.

 

Yeah I figured that after posting. It's the turbo vs manifold pressure differential which opens it.

I do have a loping idle. I've been meaning to see if it's leaking. I'm going to do the easy test.
Tape over the BOV holes and see if the idles clears up

 

it may be your running to rich mine was doing it bad with my 2.5" exhaust I put a #" on and it got a lot better now only drops a little at 6K RPM's and I have a stock s4 turbo with stock wastegate.