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?

[quote name='DamianSoul' date='Sep 12 2005, 02:38 PM']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?


[/quote]



What RPM does your boost taper off at?

[quote name='APE RX7' date='Sep 12 2005, 01:36 AM']What RPM does your boost taper off at?


[/quote]



After shifting to second my RPM is usually around 4500. From here boost builds quickly, then tapers off. By the time I am at 5500 I have no power.

you need to look at your ENTIRE rat's nest and check for broken solenoids and check valves. I think there is a diagram still up at www.scuderiaciriani.com, unless steve finally did the change over to the new website name... but he should have a link to the new site. Lots of good info there for you anyway. But basically, your second turbo isn't coming online.. could be a few different things that cause it. Start by checking for loose/broken hoses under the UIM.

how many miles are on the turbos?

nah 99% i bet its a vacc hose or solenoid issue. Sounds like you need to do a hose job and check all the solenoids to me..

Rat's nest was done three months ago, and all solenoids were replaced. The turbos have ~80,000 on them, but they are both coming online according to the data logs. I've spoken with other people about this, including Tom at RotaryRX here in Albuquerque, and they agree that it is the checkvalve on the vacuum chamber in the boost system.

yep and your turbos are getting worn out too, start saving for some upgrades !

I had the same problem, bad check valve, $32.



Good Luck,



2 turbos