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Weird Sound When Coming On Boost And Loss Of Power

SlowGTS-t

By SlowGTS-t,
in Engines & Forced Induction

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SlowGTS-t Contributor

SlowGTS-t

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I've got an RB20DET with FMIC, AVCR, exhaust, filter and an aftermarket turbo (supposedly a rebuilt RB25) and a reprogrammed ECU.

Hits full boost by about 3500 rpm but then the car feels like its losing power, turbo starts making a shuffling sort of noise, the boost gauge neede starts to dart left and right really quickly. Once above 4500 rpm, the problem goes away and the car pulls hard to 7500rpm.

Is this compressor surge? The turbo is meant to be a stock RB25 unit with steel internals and plain bearings so it shouldnt really happen. If it is surge then its a really bad thing right?

BHDave Grand Master

BHDave

Posted
Posted

It could be surge (but i doubt it), it could be a bad miss due to bad coils or really rich mixtures. Eliminate the possibility of a miss first i think.

Get it on a dyno for a power run. An experienced operator will be able to tell you exactly what it's doing.

SlowGTS-t Contributor

SlowGTS-t

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It could be surge (but i doubt it), it could be a bad miss due to bad coils or really rich mixtures. Eliminate the possibility of a miss first i think.

Get it on a dyno for a power run. An experienced operator will be able to tell you exactly what it's doing.

Good idea but was trying to find the no cost solution.

Would a miss go away at higher RPM?

SlowGTS-t Contributor

SlowGTS-t

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It sounds more like surge to me. Especially with a rebuilt rb25 turbo. Could be one of the older stage 2 gcg turbo's which had big surge problems on rb20's.

Bent out wastegate arm (very little preload on actuator now) which makes boost come in later. No more surge but not a lot happening until 4000rpm. MIght play with arm a bit more....

Cheaper I suppose than changing exhaust housings / wheels...

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