Fuel Pressure Question

89fast5oh · 12-13-2005, 05:25 PM

When adjusting fuel presure, does fuel delivery increase with fuel presure increase. Also does turning the fuel presure up make the car lean or rich.

Thanks
Kevin

~The Jester~ · 12-13-2005, 07:43 PM

No, the exact opposite happens. Provided an ample and adequate supply, as pressue INCREASES, volume DECREASES. Picture holding your thumb over the end of a garden hose. Pressure?? Hell yeah! Volume?? Not so much.

If you're tuned correctly, fuel pressure shouldn't affect rich/lean one way or the other. Let me state that I'm referring to a CARB here, not sure what you're running. Anyways, the carb will take what it wants/needs/is available. Except for extremes Rich/Lean is your TUNE, not fuel pressure. Extremes being fuel starvation will cause a lean condition, as blowing past the needle/seat (or float levels set too high) will cause a rich condition.

89fast5oh · 12-13-2005, 09:52 PM

Sorry I should of stated that I was running EFI. The combo is in my sig. Right now I have a 190lph pump, think that is enough for my current combo?

~The Jester~ · 12-13-2005, 10:53 PM

I'm pretty good with a carb, and fuel systems in general, but I know poopy about EFI.

Let's wait for one of the EFI gurus to pipe up in here, K?

I shoulda read your sig, my bad.

Unit 5302 · 12-14-2005, 12:29 AM

Higher fuel pressure does allow the system to deliver more fuel to the engine. That being said, changing the fuel pressure will not really create a lean/rich fuel mixture so long as you stay within the air fuel ratio tables available to the computer.

As your fuel pressure increases, the EEC will adjust the duration of the injector to bring the air/fuel ratio back into spec.

Increasing fuel pressure may have the advantage of more complete atomization of the fuel, allowing a more efficient and consistent burn. Of course, this depends on what fuel pressure you're running at currently. Anything below 30psi will result in a less than ideal spray pattern and atomization, and I don't expect you'll see any real gains in atomization or efficiency above 40psi.

I'd expect your combination to be producing anywhere from 400-425hp N/A properly tuned. With your 30lb/hr injectors, you won't need anything more than the stock 40psi pressure. Quite frankly, depending on how much power your engine makes, the 30lbers may be a little more than you need, but stepping down to 24lb/hr units would definitely require significantly greater pressure than stock.

89fast5oh · 12-14-2005, 12:34 AM

Thats about the power number I came up with, anywhere from 400-435. Since this is winter season, and the car just sits in the garage I'll have to wait a few months to get it to a dyno. Then I can really get things dialed in correct.

12-13-2005, 05:25 PM	#1
89fast5oh Registered Member Join Date: Apr 2002 Location: Canada Posts: 56	Fuel Pressure Question When adjusting fuel presure, does fuel delivery increase with fuel presure increase. Also does turning the fuel presure up make the car lean or rich. Thanks Kevin __________________ 351W .030", AFR 185s, Crane roller cam-.543" 220 -.562" 228@.050, TFS 351W EFI intake, Billet Roller Rockers, BBK Long Tubes, BBK X- Pipe, Dynomax Race Magnums w/dumps, 30lb injectors, 190lph intank pump, Holley Adjustable FPR, 75mm TB&MA, Underdrive pulleys, Aluminum Rad, Billet Flywheel, McCloud Clutch, World Class T-5, B&M Ripper Shifter 4.10s, McCreary G-60s, Lakewood 90/10s, Comp. Enginering 3 way adjust/rear, Upper and Lower Control arms, Autometer gauges.

12-13-2005, 07:43 PM	#2
~The Jester~ Rat Killer Join Date: Aug 2002 Location: Cold ass Ohio Posts: 1,143	Re: Fuel Pressure Question No, the exact opposite happens. Provided an ample and adequate supply, as pressue INCREASES, volume DECREASES. Picture holding your thumb over the end of a garden hose. Pressure?? Hell yeah! Volume?? Not so much. If you're tuned correctly, fuel pressure shouldn't affect rich/lean one way or the other. Let me state that I'm referring to a CARB here, not sure what you're running. Anyways, the carb will take what it wants/needs/is available. Except for extremes Rich/Lean is your TUNE, not fuel pressure. Extremes being fuel starvation will cause a lean condition, as blowing past the needle/seat (or float levels set too high) will cause a rich condition. __________________ d-Con Racing "Nothing fancy, just 347 inches of RAT POISON!" MICE need not apply.....

12-13-2005, 09:52 PM	#3
89fast5oh Registered Member Join Date: Apr 2002 Location: Canada Posts: 56	Re: Fuel Pressure Question Sorry I should of stated that I was running EFI. The combo is in my sig. Right now I have a 190lph pump, think that is enough for my current combo? __________________ 351W .030", AFR 185s, Crane roller cam-.543" 220 -.562" 228@.050, TFS 351W EFI intake, Billet Roller Rockers, BBK Long Tubes, BBK X- Pipe, Dynomax Race Magnums w/dumps, 30lb injectors, 190lph intank pump, Holley Adjustable FPR, 75mm TB&MA, Underdrive pulleys, Aluminum Rad, Billet Flywheel, McCloud Clutch, World Class T-5, B&M Ripper Shifter 4.10s, McCreary G-60s, Lakewood 90/10s, Comp. Enginering 3 way adjust/rear, Upper and Lower Control arms, Autometer gauges.

12-13-2005, 10:53 PM	#4
~The Jester~ Rat Killer Join Date: Aug 2002 Location: Cold ass Ohio Posts: 1,143	Re: Fuel Pressure Question I'm pretty good with a carb, and fuel systems in general, but I know poopy about EFI. Let's wait for one of the EFI gurus to pipe up in here, K? I shoulda read your sig, my bad. __________________ d-Con Racing "Nothing fancy, just 347 inches of RAT POISON!" MICE need not apply.....

12-14-2005, 12:29 AM	#5
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	Re: Fuel Pressure Question Higher fuel pressure does allow the system to deliver more fuel to the engine. That being said, changing the fuel pressure will not really create a lean/rich fuel mixture so long as you stay within the air fuel ratio tables available to the computer. As your fuel pressure increases, the EEC will adjust the duration of the injector to bring the air/fuel ratio back into spec. Increasing fuel pressure may have the advantage of more complete atomization of the fuel, allowing a more efficient and consistent burn. Of course, this depends on what fuel pressure you're running at currently. Anything below 30psi will result in a less than ideal spray pattern and atomization, and I don't expect you'll see any real gains in atomization or efficiency above 40psi. I'd expect your combination to be producing anywhere from 400-425hp N/A properly tuned. With your 30lb/hr injectors, you won't need anything more than the stock 40psi pressure. Quite frankly, depending on how much power your engine makes, the 30lbers may be a little more than you need, but stepping down to 24lb/hr units would definitely require significantly greater pressure than stock.

12-14-2005, 12:34 AM	#6
89fast5oh Registered Member Join Date: Apr 2002 Location: Canada Posts: 56	Re: Fuel Pressure Question Thats about the power number I came up with, anywhere from 400-435. Since this is winter season, and the car just sits in the garage I'll have to wait a few months to get it to a dyno. Then I can really get things dialed in correct. __________________ 351W .030", AFR 185s, Crane roller cam-.543" 220 -.562" 228@.050, TFS 351W EFI intake, Billet Roller Rockers, BBK Long Tubes, BBK X- Pipe, Dynomax Race Magnums w/dumps, 30lb injectors, 190lph intank pump, Holley Adjustable FPR, 75mm TB&MA, Underdrive pulleys, Aluminum Rad, Billet Flywheel, McCloud Clutch, World Class T-5, B&M Ripper Shifter 4.10s, McCreary G-60s, Lakewood 90/10s, Comp. Enginering 3 way adjust/rear, Upper and Lower Control arms, Autometer gauges.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Speed Secret # 3	jim_howard_pdx	Windsor Power	13	11-09-2002 10:35 AM
Fuel pressure question	MEDIK418	Windsor Power	2	10-26-2002 02:45 PM
is my fuel pressure too high under boost?	bullitt843	Windsor Power	4	04-26-2002 07:32 PM
Fuel pressure at high altitude. etc...	Dark_5.0	Windsor Power	5	04-19-2002 07:52 AM
fuel pressure, TPS setting, and timing for supercharger	gramsch	Windsor Power	5	05-07-2001 12:16 PM