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Strange boost fall off at higher rpms

Old 06-08-2009, 08:35 PM
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Default Strange boost fall off at higher rpms

Im running into a situation that at 6k rpms the boost level will drop for 10 psi to say 9/9.4 psi. im wondering if the cams (stock) are not big enough and creating a blockage or if the exhaust is too small or the timing isnt enought. any ideas?
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Old 06-09-2009, 03:02 AM
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the real question is. what does boost falling off have to do with engine managment
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Old 06-09-2009, 07:32 PM
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sorry about that, may have put it in the wrong forum, if a moderator wants to move it.
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Old 06-10-2009, 12:13 AM
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Exhaust gas leak before the turbine housing? i.e. - Manifold to Head. Manifold to turbine inlet.

Wastegate spring isn't holding? Maybe the turbine housing is too small and since it's being over run, blowing the wastegate open no matter what?

Let us know so we can help.
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Old 06-10-2009, 12:35 AM
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im going to guess it is a small exhaust leak on either of the gaskets between the head and the turbo. get some copper spray and use that on the gaskets it helps alot
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Old 06-12-2009, 05:51 PM
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its a evo3 16g thats been ported rated to 22psi so that shouldnt be it.
i dont run gaskets from the manifold to turbo. i have the edges strait edged or what ever its called at the machine shop for a perfectly flap seal. i did run tape around it just in case and ran it and the tape didnt blow out anywhere so theres no leak. only leak i have is the downpipe and o2 housing.
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Old 06-12-2009, 09:23 PM
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how big of a leak is in the down pipe and how far away from the turbo is it? also what about a leak from the head to the manifold
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Old 06-14-2009, 07:57 PM
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do you have a pinhole boost leak some place? 10psi at 2000 rpm and 10psi at 6000 are different yes its the same pressure in the intake but a hell of a lot more flow is going through the pipes. that then causes more force to be in place on the couplers clamps etc. aside from the exhaust i would build a simple boost leak tester using a coupler some pvc and an air regulator set it to 12psi and hook it up to the inlet of the compressor pressurize the system with the throttle blade closed to see if you hear air coming from anyplace.
If is you should not only hear it but grab some soapy water and spray all the couplers and look for bubbles.
on this same note is your bov leaking?
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Old 06-17-2009, 07:48 PM
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no leaks from the head to manifold, i will assemble a boost leak tester and report back
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Old 06-21-2009, 03:46 AM
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Minor boost leak
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