F.I. fuel pressure theories

[Pierce Jones]

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.

[Stan Weiss]

Originally Posted by Pierce Jones

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.

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

[Dave Noll]

Spraying onto a closed intake valve is losing the advantage of Sequential injection. Makes it similar to having a carb on it.

[Pierce Jones]

Originally Posted by Stan Weiss

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

I'm new to FI, only self taught and going on 3 seasons. I just got back from the chassis dyno. Engine is an LT1 with Holley HP. Running 24 lbs/hr @ 70 psi, log shows 7.99 msec, 90% duty @ 7000RPM. Chassis dyno showed 415hp ish

Stan - Maybe Holley calculates duty cycle on 360degrees?

Unfortunately I didn't have a larger set of injectors to throw in and try.

My biggest issues continue to be hot start and idle quality, decided to try and sort that out at home instead of on the dyno.

I started playing with the Injector End Angle (IEA) Table for the first time. Very slick in V5, essentlially plug in cam specs and it calculates IEA based on fuel table. My set-up uses the crank tigger only.

[Stan Weiss]

Originally Posted by Pierce Jones

I'm new to FI, only self taught and going on 3 seasons. I just got back from the chassis dyno. Engine is an LT1 with Holley HP. Running 24 lbs/hr @ 70 psi, log shows 7.99 msec, 90% duty @ 7000RPM. Chassis dyno showed 415hp ish

Stan - Maybe Holley calculates duty cycle on 360degrees?

Unfortunately I didn't have a larger set of injectors to throw in and try.

My biggest issues continue to be hot start and idle quality, decided to try and sort that out at home instead of on the dyno.

I started playing with the Injector End Angle (IEA) Table for the first time. Very slick in V5, essentlially plug in cam specs and it calculates IEA based on fuel table. My set-up uses the crank tigger only.

Pierce,
I have never used the Holley system and so do not know how it works.


Maybe Rob from Holley will see this thread and explain it.


Based on my understanding of what you have, and running some numbers I believe the 90% is correct. I believe the 7.99 msec (what should be the pulse width) is not correct.


Stan

[e vassar]

Thanks for the great advice...although I understand little of it.....I think I will not change those injectors for now. I think my ECM is close, just needs a little tweaking. I am willing to pay someone down here in D4 to throw a laptop on it!