Any ideas what would cause my mates car not to hold its boost? new turbo and actuator fitted, peaking at 15 psi then dropping off to 10-11 psi, any ideas what to look out for? he's thinking of ordering a Apexi boost controller--i presume that should help. any ideas????

 

Are these standard parts, or an aftermarket turbo setup? Also do you know what the pressure rating on the wastegate spring is if its not stock? Typically you see the boost drop like this mostly when the turbo is insufficiently sized and runs out of airflow at high rpm, but there are other possibilities as well. If the turbo isn't sized right no boost controller will help the problem.

 

Leak

 

w/o knowing your mods, it sounds like you have little restriction in the exhaust and/or intake. a boost controller often helps in that situation as the stock solenoids often don't respond quick enough.

 

Restriction on the exhaust will make that low gain because when I had a cat back it boosted 13-14 and when I installed the stocker the boost went down to 10!!! Just because of the restriction.