damian

iTrader: (2)

can someone clarify the following for me...

70lb injectors = 720 cc ?
160lb injectors = 1680 cc ?

fuel pressure at idle should be what with vac attached? (30ish?)
fuel pressure at idle should be what with vac NOT attached? (40ish?)

thanks

maxcooper

70 lbs/hr ~= 737 cc/min
160 lbs/hr ~= 1684 cc/min

Fuel injector size ratings are given for a "standard" (arbitrary) base pressure of 43.5 psi. They will flow more at higher pressure and less at lower pressure, but even if you aren't running 43.5 psi base pressure, it is customary to enter the injector flow rates that the standard pressure gives. The conversion from lbs/hr to cc/min includes an assumption about fuel density; this isn't a problem, just an FYI.

You can set the base pressure to anything you like; there isn't a "correct" pressure. But ~40 psi with the manifold reference hose detached from the regulator (= base pressure = effective pressure) is a reasonable setting. Higher base pressures put more stress on the fuel pump and plumbing and can make your idle rich if you are at the limits of your ECU's resolution (though injector lag time is perhaps an even more important setting for idle mixture), but will provide more flow if your fuel pump is up to the task. Lower pressures might give a poor spray pattern, but could possible make idle mixture tuning easier and puts less stress on the fuel pump and plumbing.

In summary, I suggest:
- enter 737 cc/min as your primary sizes
- enter 1684 cc/min as your secondary sizes
- (or alternately, enter 720 and 1600 since they are "scaled" equally -- the ECU really just needs to know the correct ratio of primary to secondary sizes so it can do the transition right -- the actual sizes / scale factor you use doesn't matter so much as long as it is reasonable [don't enter 72 and 160 for fear of rounding errors or going off the limit of the adjustment range in the fuel map -- you'd need 10x the settings for these!] once the car is tuned)
- set the base pressure (FPR manifold reference signal hose removed) to 40 psi, this will give an idle pressure of ~32 psi or so, depending on manifold vacuum

-Max

damian

iTrader: (2)

max, you are the man!!!

this is the exactly what I wanted to know and the detail I wanted to understand it :-) thanks