trying to understand how to adjust the FMU, so i created a little chart to help me visualize what's going on...
* when the engine is operating not boosted (as if NA) i want the engine to run close to its stock fuel delivery calibration, and so i need stock fuel pressure up to the "NA WOT" point; that's the BLUE line
* the stock fuel pressure regulator will control to about a 1:1 ratio, so only another 8 psi or so will be generated when the turbo begins to build boost
* let's assume that i need 40 psi additional fuel pressure for my 8 psi turbo
* that means i'll need a 5:1 FMU; that's the RED line
* it will reference pre-throttle body pressure (non vacuum), otherwise it alters my non boosted fuel pressure too much
* so as to maintain the stock pressure during non-boosted operation, i need to adjust my FMU base pressure to no higher than 40 psi; that way the stock FPR has control during that part of the operating range
* the resulting pressure curve is the upper combination (max value) of both lines
So, my question is, since the FMU doesnt really begin to add any supplemental pressure until 3 psi of boost or so - will that create a dead spot during that transition?
if i adjust my base FP up by 5-10 psi to get rid of that "flat" spot, i'm afraid the engine will run too rich at the low end (the NA portion).