boost creep/overboosting issues

[Zelfear]

Im having an issue with boost creep. Boost will shoot to 6 or 7 hoover for 5-700 rpm and then climb to 12-15. Heres my setup apexi power intake, lexus afm, 550cc, nonturbo pistons .5mm over, ported stock exhaust manifold, (I think) bic 3" divorced (recirculated) dp, 3" straight pipe to an apexi n1 muffler, and a light weight flywheel.

Ive tested the wg actuator starts to move at about 5psi. Linkage moves freely pulled the down pipe off. The divider plate was slightly bent but I don't think it was enough to cause an issue. Where the dump pipe comes back into the main exhaust there is about a 1/4" or more lip all the way around where the hole in the main exhaust is smaller that the dump pipe. Not sure if this is an issue or not.

Im wondering if the nonturbo pistons and slight over bore are not part of the problem also. My plan as of now is to port the wg hole in the turbo an open up the hole where the dump pipe goes into the exhaust. Any other ideas or suggestions?

 

[Insidious Surmiser]

Better take some measurements and make sure the divider on the DP isn't causing clearance issues. Other than that, is it creeping in every gear?

From what I understand, the WG partially functions by creating turbulence in the exhaust (restricting turbine flow). Porting the WG should fix the issue.

My car would always creep a lot using a DDP. Mainly in 4th and 5th gear, although you're not supposed to go WOT in 5th.

 

[Zelfear]

Well it doesn't seem to do it in first gear although I don't usually get on it in first and It will go to 10 or 12 psi in 2nd gear but in 3rd and above it goes all the way to 15 Psi. the divider definitely was not hitting the waste gate valve but I was wondering if it was causing the main exhaust to get in to the dump tube and not allowing enough preturbo exhaust out.

 

[hvyman]

Id start with porting the wastegate hole.

 

[reeds420]

I am having the same issue with my SP61GT. It will open at around 8psi and creep all the way to 18psi. I ported out the wastegate dumptube hole on the divorced downpipe, ported out the wastegate hole on the hotside of the turbo, and went from a 15psi wastegate actuator to a 10psi one and the problem still remains. The wastegate flapper is not hitting the tab on the DDP either. All this boost creep started when I had the tab welded onto my DDP. It didn't do it beforehand. So I'm probably going to remove it. Like stated before, try to port out your hole on the DDP and turbo hotside. If that doesn't work I'd remove the tab. Just an idea...

 

[Backlash2032]

Have the same issue with my stock CT.. shimmed wastegate, builds to 9 pounds. Then creeps to 11 pounds. 12 pounds and fuel cut in 3rd gear.

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[reeds420]

to give you an idea of the difference the tab made, for me at least, with the tab installed the wastegate opened at 8 psi and crept fast to 18 psi and hit fuel cut before i hit redline. i removed the tab and now the wastegate opens at 8psi and slowly creeps to 16psi by redline. now i can use my boost controller to control boost a little bit better.

 

[Backlash2032]

Well I'm just on a widemouth. I really don't know why it's creeping so hard. Today it hit 14 psi before I even got to 4k rpm... Maybe a bad actuator? Last year when I first shimmed it it held 10 pounds great..

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[reeds420]

it may just be back pressure since the wastegate and the turbine exhaust air are trying to escape from one hole versus two on a divorced downpipe.

 

[Backlash2032]

But when I first shimmed it it didn't creep. Didn't change a thing except now it creeps lol

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[reeds420]

sorry man i thought you were the OP lol. anyways, id check the vacuum hose going to the wastegate actuator to the compressor housing first. could be cracked or leaking. seems logical if you haven't changed anything

 

[Backlash2032]

Yeah it might be.. might have to replace the old constant tension clamps on it.

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[Backlash2032]

Well.. pretty sure I found my issues.. first off my wastegate arm was hitting my dipstick tube.. and second of all my wastegate flapper was stiff as hell.. hopefully fixing this will fix my issues and I can hold 11 pounds lol

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[hvyman]

With the actuator hooked up its supposed to be pretty stiff. With it unhooked the flapper should move freely.

 

[Backlash2032]

Yeah I unbolted the actuator and moved it down a little so it wasn't hitting the turbo.. felt like it was all still bolted up except it didn't return lol

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