F.I. fuel pressure theories

e vassar · 03-25-2021, 08:21 AM

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?

Stan Weiss · 03-25-2021, 10:27 AM

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

Pierce Jones · 03-25-2021, 10:53 AM

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.

e vassar · 03-25-2021, 11:44 AM

Quote:

Originally Posted by Stan Weiss

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

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

Stan Weiss · 03-25-2021, 12:11 PM

Quote:

Originally Posted by e vassar

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

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

KRatcliff · 03-25-2021, 12:48 PM

Quote:

Originally Posted by Stan Weiss

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

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

YMMV.

Stan Weiss · 03-25-2021, 02:17 PM

Quote:

Originally Posted by KRatcliff

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

YMMV.

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

Stan

Bobby Fazio · 03-25-2021, 04:45 PM

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.

Pierce Jones · 03-25-2021, 05:55 PM

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 · 03-25-2021, 06:44 PM

Quote:

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

03-25-2021, 08:21 AM	#1
e vassar Member Join Date: Jul 2015 Posts: 358 Likes: 63 Liked 238 Times in 93 Posts	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?

03-25-2021, 10:27 AM	#2
Stan Weiss Senior Member Join Date: Apr 2020 Location: Phila, PA Posts: 660 Likes: 0 Liked 584 Times in 315 Posts	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

03-25-2021, 10:53 AM	#3
Pierce Jones Junior Member Join Date: Aug 2013 Location: Chatham, ON. Canada Posts: 19 Likes: 15 Liked 15 Times in 9 Posts	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. Last edited by Pierce Jones; 03-25-2021 at 05:06 PM.

03-25-2021, 04:45 PM	#8
Bobby Fazio VIP Member Join Date: Nov 2009 Location: Egg Harbor Township, NJ Posts: 1,420 Likes: 1,269 Liked 3,863 Times in 456 Posts	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. __________________ '65 Mustang SS/L & L/SA DriverInterviews.com \| App.DragInsights.com

03-25-2021, 05:55 PM	#9
Pierce Jones Junior Member Join Date: Aug 2013 Location: Chatham, ON. Canada Posts: 19 Likes: 15 Liked 15 Times in 9 Posts	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.