so i went to the track last friday and found out that at WOT the most boost i can build is 2psi. The car would build full boost at WOT throttle before, the only thing i changed was i put flanges on my y-pipe that day to get rid of a pretty big exhaust leak i had on my driver side header. i'm stumped because it only happens at WOT, at 3/4 it'll build 7 psi perfectly fine, but the second i put the pedal to the floor my boost drops to 2 psi and won't go up. I can't figure out what might be causing this so i thought i would ask you guys.

one more thing i forgot to add. before i flanged the y-pipe to fix my exhaust leak i would only build 2-3psi in first gear. after i flanged it i could build 6 psi. So at the track i would hit 6psi in first gear. but the second i shifted into second it would drop to 2psi, then while it was shifting into third gear the boost would jump up to about 4psi but immediately drop back down to 2 psi once it got into gear.


info on the car:
1995 z28 camaro
Stock 5.7l lt1 motor (stock internals)
runs 7psi
garrett tp38 turbo 1.10 a/r intake 0.84 a/r exhaust
custom remote mount i custom built
automatic transmission with a small corvette 2k stall

 

no one?

 

Sounds like you have a coupler slipping off under boost, but going back on when not. Or you still have an exhaust leak somewhere

 

it holds 7psi fine at 3/4 throttle though which rules out boost leak or exhaust leak to me. and i'm 100% sure there are no exhaust leaks, just took all my slip fit connectors and clamps off and welded flanges everywhere.


i notice that my air filter was covered in dirt yesterday so i took it off and cleaned it, went from black to white so i'm thinking maybe the filter was too restricted and at WOT it could only flow enough to make 2psi? seems kind of unlikely since the the actual filter element is a huge 4"x9" cylinder, but on my way home from class today with the cleaned filter i mashed the gas once and it held at 8-9psi @ WOT so looks like it could have fixed my problem, will have to do some freeway testing to be 100% sure

i had a shield on my filter before but i took it off when i was doing some work and never put it back on because i didn't realize how much it did! so after cleaning my filter i put it back on

 

That sounds like the problem, I was going to ask you if you put a new aire filter on recently. Turbos need massive amounts of air, glad it was a simple fix!

 

on my way to work i blew my damn intake elbow out of the coupler so i didn't get to test it. then the next day i blew my radiator hose... so i still haven't gotta a real test yet, hoping to today on my way to a job interview... or maybe i should wait until i'm on my way home..

 

that didn't fix that problem, still drops to 2psi as soon as i go WOT and stays there

3/4 throttle and it hits 7psi fine and pulls like crazy

 

I just reread your original post. You said at the end there, "once it got into gear". Does it not shift real hard in the upshifts? Or is it lazy when upshifting?

 

Is it going pig rich at wot? Slow lazy combustion or blown out spark plugs will not push the turbine.

 

I'm thinking maybe that turbo is too small and can't keep up at wot at upper rpms.

 

is it blowing the wastegate open?

 

correct! we have a winner! haha

the wastegate has a weak 3psi spring in it so it wasn't closing, apparently when i fixed my larg exhaust leak it caused too much pressure in my exhuast for that wimpy little spring to hold it closed. i re-routed my vaccum lines the way they're suppose to be with a boost controller, i originally had it just restricting the airflow going into the bottom port so it would make 7psi. now i have a line going into the bottom port, and my boost controller set-up on the top port. so far it holds 5psi @ wot fine gotta adjust the mbc to bring it up to 7 now

thanks guys

 

no, it's a built transmission and shifts a lot harder than i'd like for my dd i guess i kind of worded it wrong it was just when the car shifted it shot to 4psi really quick but dropped off pretty much instantly

 

glad i could help !!