Originally posted by Josch:
Did you know that the most automakers change fuel pressure via manifold vacuum to compensate for fuel pressure vs intake manifold pressure? So why would it be hack to further compensate fuel psi under pressures above atmospheric as well (i.e. boost). So your saying that the automakers have hacked our cars? The real hack way is to keep the fuel pressure always set at one fixed point and only change pulse width to compensate for the differential. To each his own I guess? I still think I would rather have the pressure diff compensated physically at all times. Then you could leave the factory's fuel curve more like stock. But what do I know? Maybe the factory's way is the wrong way?



First: The stock regulator alows 45psi idle and 55 psi WOT on the return style contours. Fuel pressure is plenty high even if you don't increase to compensate for boost pressure.

Second: The stock pressure regulator is still hooked up to the vacuum/pressure line. this means that if there is 6psi in the manifold it will apply 6psi to the pressure regulator diaphragm. I measured the diaphragm out to be approximately 1 in^2 so that adds about 6psi to the the spring pressure, in effect negating the increased pressure in the manifold, if not a sight increase in pressure.
Given this initial situation, I recommend ignoring 'fuel pressure' as your method of adding fuel and using the larger injectors. For our cars it is unusual to see high boost pressure, pressures over 10psi so this stuff isn't a really big factor.

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black