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Wouldn't the ecu see a different voltage for the same amount of vacuum if you changed from a 2 to 3 bar MAP sensor? Or 1 to 2 bar?
At idle (high vacuum) it would be ok, but before the boost came on the voltages would be different.
Well, I dunno
I have no index of volume metrics. That is, AFAIK, 2 psi will attain my goal of moving the peak power level down to my usable range (2500-3200) ..or about a 25% reduction in rpm. I'm not sharp enough to integrate the differences in VME based on what I've read. I mean, for all I know 1-2psi is not enough to do what I want to do ..yet I think that 5-15psi is way more (in observed/accepted performance levels of engines that use that range) than I want tweak for. I've really got to manage that cam overlap as not to blow the spent combustion material into the exhaust. I need back pressure to contain this process. Hence, as boost is elevated, so must back pressure. I've got to manage a "collision" of the two forces in balance. Ideally, I'd just, more or less, "keep ahead" of the engine's demand for air and keep a static 1-2psi above the throttle plate and let the intake float at low(er) vacuum while in the range that I need the power. It would be easier to reason if I wasn't so blind. I don't know the VME @ the peak power level where the stock 125+/- @ WOT with the 60mm throttle body and the intake manifold configuration. If I did, then I could integrate that to a CFM ..and then somehow massage that in some manner to move that CFM down about 25% (I think the hp peak is something like 4500rpm - I want it at 3200 rpm). It can totally run out of steam beyond that point and remain flat from 3200 rpm on up and just return to the normal anemic engine that it is.
On the 2 BAR MAP. I'm banking on the adaptive cells in the PCM to reindex the fuel map. What the engine will think, for a bit, is that it's either at way sub-sea level, or at a decent throttle opening. In closed loop it should be just fine using all the inputs (I hope) and this should increment the injector pulse width to compensate. It would do the same thing, over a longer span, (or so I reason) if my injectors clogged to 50% output. It would broaden the pulse width at a given MAP reading to predict a balanced O2 reading.
Now it may not be that simple. I may find that, initially, it runs perfectly fine in closed loop, but can't even idle as the engine switches back and forth between the two states. I still haven't gotten down to the dealer to look at the 2 bar MAP to see how easy it is to integrate it to my manifold/throttle body.
Thanks for the link. It's very informative. I wish there was one of the Garret turbo engineers on the board. It would sure cut out a whole lot of R&D out of the project.