squealingtires

iTrader: (14)

What is the acceptable range that the fuel pressure might change from idle to wide open throttle?

My Summit, fuel-rail mounted, guage shows about 62psi at idle then when I crack the throttle it drops. What would be the lowest acceptable pressure given 36lb injectors on a NA 402 stroker?

I don't have a guage inside the car so would this test even be worthwhile since I'm not seriously loading the engine when I'm reving it up?

squealingtires

iTrader: (14)

anyone?

dynocar

You should not see hardly any change with out loading your engine. What you should be most interested in is what is your fuel pr at WOT, at your high RPM shift point, and the engine fully loaded like on a track, street or dyno. Should not see more then a 5 - 6 Lb drop on an LS1 then.

squealingtires

iTrader: (14)

Would anybody conclude that I have a fuel delivery problem if the fuel line pressure drops instantly when going from idle to about 2500 rpm this is unloaded when the car is in neutral?

I'm running a GM performance 225 pump.

dynocar

I cannot remember what the in tank fuel pressure return system looks like so I'm talking a little out of school here but I'll continue anyway. One possible explanation for this is that you have a fuel pressure regulator return line restriction now due to the increased volume of your fuel pump. When you increase the RPM of the engine the injectors flow more fuel thus reducing the amount of fuel flowing back thru the return line of your in tank regulator. This reduced flow back decreases the restriction and backpressure thus decreases your rail fuel pressure. Your fuel pressure should stabalize once this restriction is reduced. If this is the cause it would only be a problem at closed throttle if a problem at all. This could cause your fuel trims to go more negative at idle and that could be tuned out. Many have this problem with large pumps and live with it. Again, more importantly what is your pressure at full load, WOT, peak RPM? A dyno test or putting an extention on your FP gauge mouted to your windshield wiper could tell you.

squealingtires

iTrader: (14)

Thanks, that's the kind of informaton I'm looking for. I will be looking for a fuel guage for the cockpit this weekend then. Thanks again for the help