I have a boost issue that happens about one out of every five times and I'm not sure where to begin looking for the source of the problem. Here is my setup:

PowerFC
Stock twins set for 0.70 BAR (~10 PSI) and 64% wastegate duty for both turbos.

I accelerate hard through first gear verifying a normal boost pattern. I shift to second and accelerate hard. The boost builds up quickly, but begins to taper off causing an increasingly sluggish feel to the point where RPM's almost stop increasing. In other words I'm going nowhere. If I take my foot off the accelerator for a second or two, then accelerate hard again, boost builds up and exhibits a normal pattern.

Could this be a tuning or mechanical issue?

 

I'm guessing mechanical. My answer for everything is solenoids cause that exact thing happened to my FD, but apparently it can be caused by a number of things.

 

Mechanical. It sounds like the one way check valve on the vacuum chamber in your turbo system is leaking. Letting off the throttle pulls vacuum back into the chamber, restoring boost.

 

My friend had similar problems in his sr20det powered 240 but a little tinkering with the profec b spec fixed that. No help to you but good luck.

 

As Kento said, you have a problem with your vacuum chamber, most likely with the check valve.

 

Tom at RotaryRX here in Albuquerque agrees that it is the check valve. Thanks for the help.