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GJF GJF is offline
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Join Date: Dec 2004
Posts: 801
Exactly rsrmike!

Now that you have the FPR sensing MAP, unless you were lean before on boost you should now be a little rich on boost. With the MAP signal the FPR compensates for the vacuum and the boost and is variable with the present outside conditions. The ouside amtospheric pressure directly changes the manifold pressure whether it be vacuum or boost.

Having a fixed fuel pressure would need much more injector timing on boost as the boost would be fighting the fuel pressure. And then when the outside conditions change drastically the tune would be off because the tune would be on a good warm sunny day would not run the same on a humid overcast day or at lets say 12pm vs 12 am. The weather conditions are just too drastically different.

By having the FPR sense boost the fuel pressure increases to counteract the boost, and automatically enrichen the fuel. Or when you are at idle and the fuel pressure is lower due to the vacuum and you instantly romp on it. The vacuum drops to "0" and the fuel pressure rises and assist compensating the fuel demand without drastic injector timing changes.
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 08-17-2008, 08:14 AM
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