What Fuel Pressure To Run???

BowTie Eater 5 Liter · 04-25-2001, 10:34 PM

Ok, some guy I know has a 90LX Hatch & he has underdrive pulleys, full exhaust(bbk shortys, off-rd h-pipe, dynomax ultra flos) 14* timing, edelbrock intake, 1.7rrs, ported stock heads (new valves, springs...) 70mm t-body, 75mm maf, adj. fpr, 30lb injs, 3.55 gears, hurst shifter(t-5).
what psi should he set the fuel regulator at???
what hp should (could) he expect & also what 1/4 mile times could he catch???

thanks...

------------------
1988 Mustang GT, T-5
3.08's, No Smog Pump (Shorty Belt), Dumps At The End Of Stock H-Pipe, K&N Air Filter (Stock Air Box), Removed air silendcerMy Stang
My Site (Not Done Yet)

04-26-2001, 01:28 AM

Fuel pressure-- set it around 39-41psi You'll learn where the motor likes to run at it's best at a track by experimenting with raising/lowering pressure on different runs.

Why is he running 30lb injectors? He would have been just fine running 24lb. injectors.Same thing for his throttle body,he would have better throttle response with a 65mm.The 65mm supports up to 450hp,after that HP level is reached then a person is alright to move up to a bigger one.

------------------

Paxton Blown 87GT
ICQ#112698436

jimberg · 04-26-2001, 01:51 AM

Since the computer actually controls the air/fuel mixture, setting the fuel pressure hardly does anything as far as performance. It will, however, allow you to get more throughput from small injectors. Injectors are rated at 39psi. If you want your 24# injectors to act like 28# injectors, take 28 multiplied by 39 and then divide by 24. 45.5 psi would give you 28# injectors.

Adjusted Pressure = (Target capacity) * 39 / (Current capacity)

This will only work to a degree since there are physical limitations as to how short a time an injector can be open. As you boost pressure, the computer will try to compensate but since it can't open and close the injector fast enough you will start to run rich at idle.

Changing pressure will only help you with two things. If you are running out of fuel at WOT, boost the pressure. If you think the computer is running too rich at WOT, drop the pressure.

The exception to all this is immediately after you reset your computer. Since the computer has to relearn how much fuel it is dispensing, it will start with stock numbers and start learning what the new numbers should be. If you drop pressure, your car will run lean for a while. If you boost pressure, your car will run rich for a while.

Now to answer your question, set it to 32psi. Those 30#ers are too big as it is. Dropping to 32 psi should have them behave like 24#ers as Mustanguy pointed out.

------------------
351W 89 Mustang GT Convertible

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04-25-2001, 10:34 PM	#1
BowTie Eater 5 Liter Registered Member Join Date: Nov 2000 Location: Maple Ridge B.C. Canada, The Best Place In The World Posts: 871	What Fuel Pressure To Run??? Ok, some guy I know has a 90LX Hatch & he has underdrive pulleys, full exhaust(bbk shortys, off-rd h-pipe, dynomax ultra flos) 14* timing, edelbrock intake, 1.7rrs, ported stock heads (new valves, springs...) 70mm t-body, 75mm maf, adj. fpr, 30lb injs, 3.55 gears, hurst shifter(t-5). what psi should he set the fuel regulator at??? what hp should (could) he expect & also what 1/4 mile times could he catch??? thanks... ------------------ 1988 Mustang GT, T-5 3.08's, No Smog Pump (Shorty Belt), Dumps At The End Of Stock H-Pipe, K&N Air Filter (Stock Air Box), Removed air silendcerMy Stang My Site (Not Done Yet)

04-26-2001, 01:28 AM	#2
Mustanguy Guest Posts: n/a	Fuel pressure-- set it around 39-41psi You'll learn where the motor likes to run at it's best at a track by experimenting with raising/lowering pressure on different runs. Why is he running 30lb injectors? He would have been just fine running 24lb. injectors.Same thing for his throttle body,he would have better throttle response with a 65mm.The 65mm supports up to 450hp,after that HP level is reached then a person is alright to move up to a bigger one. ------------------ Paxton Blown 87GT ICQ#112698436

04-26-2001, 01:51 AM	#3
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Since the computer actually controls the air/fuel mixture, setting the fuel pressure hardly does anything as far as performance. It will, however, allow you to get more throughput from small injectors. Injectors are rated at 39psi. If you want your 24# injectors to act like 28# injectors, take 28 multiplied by 39 and then divide by 24. 45.5 psi would give you 28# injectors. Adjusted Pressure = (Target capacity) * 39 / (Current capacity) This will only work to a degree since there are physical limitations as to how short a time an injector can be open. As you boost pressure, the computer will try to compensate but since it can't open and close the injector fast enough you will start to run rich at idle. Changing pressure will only help you with two things. If you are running out of fuel at WOT, boost the pressure. If you think the computer is running too rich at WOT, drop the pressure. The exception to all this is immediately after you reset your computer. Since the computer has to relearn how much fuel it is dispensing, it will start with stock numbers and start learning what the new numbers should be. If you drop pressure, your car will run lean for a while. If you boost pressure, your car will run rich for a while. Now to answer your question, set it to 32psi. Those 30#ers are too big as it is. Dropping to 32 psi should have them behave like 24#ers as Mustanguy pointed out. ------------------ 351W 89 Mustang GT Convertible