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I know there's been lots of discussion on this, but I thought I'd try and flesh out a bit more. I haven't found any posts that really explain all that's going on, just bits and peices with some different suggestions (Eg., total BPC bypass vs. inline with BPC). Here's my understanding of what's going on. Please feel free to correct:
Normally, the BPC monitors boost pressure from the turbo, then opens the wastegate when it wants to cut off turbo boost. The ECU can control when
this happens by talking to the BPC. A necessary fallout from the mechanism is some pressure bleeding and turbo spoolup lag.
With the MBC, this process is circumvented somewhat. The MBC delays "boost reading" to the wastegate. So while the turbo is cranking out 12psi, the
"mechanism" or whatever is left of it, thinks it's less (eg., 10psi). So the wastegate doesn't open as early, hence we get stronger boost. Also, eliminating the BPC results in no turbo pressure bleeding / spoolup lag.
So when connecting inline with the BPC, you get 1/2 and 1/2. The MBC still "delays" boost reading, but the BPC can still cut off boost if it feels that it's too high and/or if the ECU senses knocking.
Am I on the right track here?
I ask this in part because the thing I don't really understand is driving the MBC from someplace else to avoid the alleged top-end power reduction.
Thanks all,
Nemo
PS. I have a '99 9-3 SE, but I'm guessing this discussion applies to a wide range of Saabs.
posted by 128.143.140...
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