F.I. fuel pressure theories
 

36lb injectors at 50 psi or 42lb injectors at 40 psi . If I am able to achieve an optimal A/F either way...which will produce more power and greater consistency? Either? My theory is the higher pressure going through the smaller orifice will produce a finer mist..or better atomization which is always better? Or not?

Re: F.I. fuel pressure theories
 

Has anyone looked at say running the 42 lb injector at say 55 PSI which would have a reduced pulse width / duty cycle verses the 36 lb injector at 50 PSI?

Stan

Re: F.I. fuel pressure theories
 

I run my 24 lbs injectors at 70 psi. Theory is the injector acts larger and high pressure atomizes fuel better. I believe Ed Wright posted on this topic in the past.

Re: F.I. fuel pressure theories
 

So turn the pressure back up to 50 and shorten the duration cycle?

Re: F.I. fuel pressure theories
 

Yes, as you increase the fuel pressure the injector flow rate increases. But if fuel needed has not changed then you need to short / decrease the amount of time that fuel is flowing.

Stan

Re: F.I. fuel pressure theories
 

Yes, that is definitely the right direction based on our experience. Larger injectors, higher FP (50 psi minimum), and reduced pulse width.


YMMV.

Re: F.I. fuel pressure theories
 

Does your ECU let you control an individual injector's flow position in the 720 degree cycle?

Stan

Re: F.I. fuel pressure theories
 

I've been wondering this also. An oversized injector to get down to a low pulse width duty cycle? This is beneficial if you can phase the injector to spray at optimal time. Or a smaller injector with higher pressure for higher mist and atomization but it stays open longer and could be spraying at a closed valve.

Re: F.I. fuel pressure theories
 

Looking at a data log, my injectors (24 lbs/hr) are open 7.7msec (88% duty cycle) at 7000RPM (42 deg/msec). The intake has 308 deg dur @ .020”. So injectors are open 323 degrees of rotation and in my case spraying at a closed intake valve.

Not sure if any would be gained by a 36 lbs/hr etc.

Re: F.I. fuel pressure theories
 

One crank rotation @ 7000 RPM is ► 1 / (7000 / 60) = 0.008571 of a second

My understanding of Duty Cycle is it is the percent of open time against 2 crank rotations (720 degrees).

1) @ 7000 RPM @ 7.7 Mill seconds pulse width I get 44.9% Duty Cycle

2) @ 7000 RPM @ 88% Duty Cycle I get 15.0857 Mill seconds pulse width

I don't know what your engine BSFC or HP is. But a 24lb injector running at its rated PSI, if I guess .45 BSFC and 375 HP, that would 2# above.

Stan