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A quick question, hopefully someone can give me a detailed as to why the following is happening !

Vehicle details, 9000 2.3T (manual), abbott ecu (+ a host of other bits)

APC controlling boost, when its run this way, it seems to boost a lot stronger and earlier down the rev range, but once the revs are passed 4000rpm the boost quickly tails off. Max 18psi, tails off to 10.5psi

However, when I run the MBC, the boost is a little slower to come in with the bang, but, it does keep boosting at a higher level beyond 4000rpm. Max 19-20psi tailing off to 14psi at 5K

Is the bang slightly less due to the slightly higher boost level the MBC is set at ? ie slightly more lag as it takes longer to hit max boost level ?

Why is this ?
 

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How about this:

Whilst the APC is working the boost pressure is set by the mapping in the ECU. To raise boost above base level, the APC valve effectively diverts all compressor pressure away from the wastegate.

The MBC bleeds some pressure away from the wastegate, meaning that there is some pressure getting through at all times, meaning that it may not close so quickly. In addition, it's likely that the ECU will be adjusting timing as a compensation for not being able to control the boost as it expects, which will increase spool up time.
 
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