I have a boost sag problem. Boost is stable up to ~5500rpm. Then it steadily drops from ~12psi to ~9psi from 5500rpm to redline.



Hallman MBC is sourced just prior to TB.
Full 3” exhaust with high flow cat
Stock intake
Bell cast manifold and DP
Garrett 2554 with 6psi actuator

Is this turbo just too small to keep boost up at the higher rpms?
Or is the wastegate being pushed open?
Do I need a helper spring or could it be something else?

Thanks

 

I would think that your wastegate is the issue, and either a stronger one or helper spring would be needed.

Not that this anything to do with it, but your injector DC sure does get high?

 

yeah, and it was way rich at high RPM in this log. duty went down as we leaned out the high rpm cells in subsequent pulls. I used this pull because it most clearly depicts my boost sag condition.

 

Throw a new wastegate actuator at it. Something in the 10psi range should help.

 

Yes.. I'm sure you know this already, but the ideal setup is to have a wastegate that holds closest to your target boost level. Then if you need a few more psi then use the boost controller to up it a few psi.

Not that people really do that, but most likely that's your problem.

 

Nope, didn't know that. But it makes sense. Thanks.

Would a helper spring effectively be the same as a new higher rate wastegate actuator, or no?

 

It may help, or even hide your problem, but it's somewhat a band-aid.

It's a cheap way to fix the problem, but of course it's not the "most correct" way to do it.