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MPI in preparation for BT

daconchslop

Autocross Champion
Location
SC
Car(s)
ACS SE/Tech
LPFP feeds HPHP. HPFP pressurizes fuel and feeds injectors. Injectors pulse highly pressurized fuel into cylinders with great precision and in an highly atomized state. Direct injection has very good control over fuel quantity and dispersion within the cylinder (thus why DI cars can make more power than equivalent port injected cars). It makes for a very even combustion event.

As air mass increases so does need for fuel. At some point the HPFP cannot pressurize the fuel fast enough to feed the injectors (remember, it is cam driven, so it is limited by RPM). You typically see this drop at peak torque and then see the HPFP recover as RPMs increase.

Once you upgrade the piston in the HPFP you can then supply the volume of fuel needed to prevent the pressure drop. In some cars, this is all that is needed to max out their turbo (like an IS20 on E85). At some point you'll begin to see fuel pressure issues over longer pulls. Now you've created an issue where the HPFP is pulling more fuel than the LPFP can provide over a long run, like 1/4 mile. Then you need to upgrade the LPFP to keep the HPFP happy. For some turbos, the amount of air mass exceeds that which the injectors can flow. At this point no matter what the HPFP provides the injectors can't flow enough. At that point you need injector headroom. Sadly, high volume DI injectors are very expensive and there are very few tuners who can successfully control them. At that point you just need more fuel mass, that is where MPI comes into play.
Excellent job...Just explaining this gained you an additional 50hp. 631hp. You the OG Diggs.
 
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