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Re: where is the waste-gate door at base boost??
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Posted by Dean [Email] (more from Dean) on Fri, 9 Dec 2005 16:05:22 Share Post by Email
In Reply to: where is the waste-gate door at base boost??, Smeter, Fri, 9 Dec 2005 15:38:14
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Lets say that the target boost is 15 PSI, in this case when you are on WOT and get to 5 PSI, you want the WG to be closed as to not spill any exhaust flow that will get the turbo spinning fast enought to get you to 15 PSI. A classic bleeder valve starts to open early and might be spilling gas flow well before you get near the target boost levels and that means lots of "boost lag". Notice that I did not say "turbo lag" as the turbo's reponse is not controling the boost response, the controller is. Note note that the BPC or APC valve is a solenoid variable "bleeder valve" which does increase "boost lag". A MBC/SMBC/MBC+A with a ball spring mechanism will keep the WG closed until very close to the target boost levels. With an typical undersized OEM turbo, a MBC can easly lead to boost overshoots and fuel cuts on many control systems. The MBC+A has a boost anticipator action that allows the WG to open soon enough to avoid pressure overshoots.

With a MBC/SMBC/MBC+A the boost comes on very fast and very non linear, which is really how a turbo is when not masked by the control system. You get used to some very different throttle techniques. That is what you can expect when the WG does not open early or at base boost.

I hope that that helps you, even though it is vague about whats going on specifically at base boost.


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