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Significant Boost Drop

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Old 08-12-18, 08:55 AM
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Significant Boost Drop

Hey Guys,
My car is an 87 TII with an s5 turbo and manifold, hks exhaust, rtek 1.8, manual boost controller, and a greddy bov. The car can build 11psi by 3800 rpm but by the time it gets near redline im seeing 2-3 psi. I've checked for vacuum leaks and can't seem to find any. I tried tightening the diaphragm of the bov without any effect, could it be the wastegate?

Thanks in advance,
Derek
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Old 08-12-18, 07:28 PM
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Sounds like a gnarly boost leak.
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Old 08-13-18, 12:48 AM
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How much wear is there on the sleeve for the waste gate flapper? The fact you initially building good boost is a decent sign.
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Old 08-14-18, 08:54 PM
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Spike I'll have to check, I wouldn't think there should be too much, the shop that rebuilt the turbo enlarged the wastegate and put a new flapper in (supposedly). I tried a new diaphragm in the blow off valve, and now its seeing more consistently 5psi at redline. I'm beginning to think that might be my culprit.
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Old 08-19-18, 10:46 PM
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Im talking the sleeve that the flapper arm goes through into the hotside housing. Just porting the gate and putting a bigger flapper doesnt handle any wear in the sleeve itself. Also, the actual spring in the stock wastegate diaphragm is only 5.5psi. Even running a MBC if you have enough backpressure in the hotside housing it can push open the flapper because there is more pressure in the housing than the stock spring can handle.
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