Overboosting problem - need help!

[Bcars]

Hi,

Looking for some help with an overboost problem I’m having with my S15.

All the usual mods and using a HKS GTRS with HKS adjustable actuator which should only hold 1 bar boost max.

Had the car tuned previously and it sat on 15.5psi flat without any problems. Had it retuned recently and it started overboosting to 18psi at high revs over 6500rpm in 3rd and 4th .

Things I’ve done to find the problem:

1) Unplugged the electronic boost controller and ran the actuator off the intercooler piping as the pressure source. It should only boost to what the spring in the actuator can hold but it still ran up to 18psi. So overboosting wasn’t solenoid/EBC related.

2) Took the adjustable actuator arm off the wastegate and tested the flap wasn’t hitting on the dump pipe or jamming.

3) Adjusted the HKS 1 bar actuator by lengthening the rod to see if that would reduce the boost. I was expecting atleast a 1psi reduction after 3 full rotations but nothing, still overboosting.

I'm leaning towards boost creep due to the wastegate being too small to clear the turbo gases. I found an old thread on here which had a very similar problem.

http://zilvia.net/f/tech-talk/168959-combatting-boost-creep-gt2871r.html

Anyone had a boost creep problem with this turbo?

Does a tune impact the boost creep?

Any help would be much appreciated.

Cheers,

[fliprayzin240sx]

Its probably boost creeping since the engine is now running more efficiently after getting retuned.

You got 2 options, keep loosening the HKS actuator and see if that actually lessen it. If it doesnt and the flapper just starts opening too soon, your only other solution is to take the turbo off and mill out the flapper hole to nearly match the flapper.

[Bcars]

Its probably boost creeping since the engine is now running more efficiently after getting retuned.

You got 2 options, keep loosening the HKS actuator and see if that actually lessen it. If it doesnt and the flapper just starts opening too soon, your only other solution is to take the turbo off and mill out the flapper hole to nearly match the flapper.

Thanks for your reply. Yeh I agree with you. I've eliminated most of the other problems and it is most likely just boost creep.

I've tried extending the HKS actuator arm to reduce boost but that doesn't help. It just makes the flapper open very early and it is laggy as hell to come on boost. But at high rpm it still boost creeps.

I've found that if I stick the restrictor/silencer into the rear muffler that drops the boost to 15psi and I can control boost a bit.

Do you reckon a divorce dump pipe would help? Or a more restrictive cat (currently using a metal high flow cat).