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High Rpm Boost Loss

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I have stared another thread but want to keep this concise.

R33GTST making 247rwkw.

Ran perfectly on the dyno and for the first week.

Now at about 5800- 5900rpm the boost drops from 18psi to 4psi (i.e. massive boost drop)

Turbo is a gcg highflow with an enlarged wastegate hole and flap for better boost control.

I have a turbotech bleed valve, also tried a simple T off to bleed boost to achieve 1 bar. Still the same problem.

Occassionally it does hold boost to redline.

It has an Rb20 actuator (holds about 0.6 bar - 9psi without boost controller).

It will hold the 9psi to redline. It will also hold 11-12 psi to redline. As soon as you boost to about 14psi the massive boost drop occurs.

Intake has been checked for leaks, cat appeared ok.

The 2 suspects are the actuator and the centre muffler.

I'm thinking of getting/buying a HKS actuator or an rb25 one to test.

It's as if the wastegate gets pushed wide open ~ 6000rpm and 15+ psi. Anybody seen one fail this way?

I have also done a lot of other checks. The tuner was a bit surprised at the problem but didnt have time to put it on the dyno.


Edited by benl1981

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I think the HKS actuators are 0.8-0.9 bar, then adjustable from there.

I thought you could get 1 bar but on Greenline etc they are only 0.8-0.9..

Hopefully it fixes the huge ~ 10psi boost drop!

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No, pretty sure its not a boost controller issue as it is holding less than the wastegate actuator pressure when boost is raised.

The intake pipe has the 10cm of metal stuck in the middle so I dont think it is that.. but yeah it does sound like the symptoms

Ordered a HKS actuator to see if that is the cure..

Edited by benl1981

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Problem was my modified air snorkel. I cut some out to create room for FMIC pipe. Sealed it up but not as free flowing.

On the dyno it was ok since less restriction with bonnet open.

It was strange that it was ok for a while. Maybe I didnt really push it over 6k before.

Took air snorkel off (still standard air box). Making just over 14psi at 6500rpm..

Edited by benl1981

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