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Does anyone have some experience with controlling boost with a sensor places before the throttle body? Bosch and many OEM's are using two MAP Sensors one before and one after the throttle body.
Think this could have some advantages like better control in part load. Any experience anyone?
From what I gather, the OEMs are using two MAP sensors to avoid needing a hot-wire MAF sensor. Knowing pressure at two points can be useful for calculating flow. I don't know enough about OEM ECU strategy to say which sensor they would be using for boost control.
MoTeC provide the option of using a pre-throttle MAP sensor for boost control. I've also tuned a couple of Mk5 VW golf 2.0 TFSI engines that user a MAF for fuel scheduling and a pre-throttle MAP sensor that I assume in stock form is utilised for boost control. The theory as I understand it, is that controlling the wastegate based on pre-throttle boost pressure can offer more stable control and faster response to large throttle transients. I can't say that I've seen this personally but I wouldn't say my use is extensive enough to really comment.
On a lot of these ECU's, they control to a pressure drop across the throttle, even in part load scenarios, especially for emissions purposes. So for example, when controlling throttle during the catalyst light off, there is a lot of spark retard and a target pressure ratio between manifold and throttle inlet pressure. It can also be used in conjunction with intake and exhaust variable valve timing.
In my opinion there is limited value in doing it with an aftermarket boost control situation, because it's really meant for complicated stock ECU algorithms.