Proper fuel pressure with 30LB. injectors

The 30 lb injectors are too big for your combo unless you have pressurized induction in your future. The stock 19 lb injectors are a better match, and will support up to 258-275 flywheel HP.

Injector HP ratings: divide flow rating by .5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines.

Example:
19/.5 = 38, 38 x 8 = 304 HP
24/.5 = 48, 48 x 8 = 384 HP
30/.5 = 60, 60 x 8 = 480 HP

The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

304 HP x .85 = 258 HP
385 HP x .85 = 326 HP
480 HP x .85 = 408 HP

Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

See Automotive Performance Software / Interactive JavaScripts Calculators to get the calculators used in these examples.

Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.




Diagram courtesy of Tmoss & Stang&2birds


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Copied from the FORD RACING PERFORMANCE PARTS catalog:
PROPERLY SIZING FUEL SYSTEM COMPONENTS
Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Here's a chart for those of us too lazy to do the math or don't have a calculator handy...

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts

60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.

kbnugggz said:

1. What should my fuel pressure my adjusted to??
2. Is it really going to make that much of a difference adjusting the fuel preussure without getting a better fuel pump??

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1. Start with stock, ~39psi with the vac line removed.
2. Yes, it will make a difference.

ok so what injector would i need for my 12.1 comp 347 since this thread is open? i mite as well ask. the car has a solid lift cam 585/600 242/257 on a 106/114, with cnc canfeild heads, holley systemax intake, pulleys, 1/3/4 lts, 70 mm tbody and 75 mm maf. i have 30s in it now with a 255 intank pump. In order for it to run half way decent i have to have 65 psi of fp at wot

ls1beater4eva said:

ok so what injector would i need for my 347 since this thread is open i mite as well ask it has a solid lift cam 585/600 242/257 on a 106/114 with cnc canfeild heads holley systemax intake pulleys 1/3/4 lts 70 mm tbody and 75 mm maf i have 30s in it now with a 255 and in order for it to run half way decent i have to have 65 psi of fp at wot o yea the comp is 12.1

Click to expand...

Your post is very difficult to read with no punctuation.

Go back and re-read my previous 2 posts. All the info you need is in there. If you engine will not run good with 30lb injectors and a 255 LPH fuel pump, you have other problems.

jrichker said:

Your post is very difficult to read with no punctuation.

Go back and re-read my previous 2 posts. All the info you need is in there. If you engine will not run good with 30lb injectors and a 255 LPH fuel pump, you have other problems.

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sorry bout the first post its fixed. its not that it doesn't run, it just spitts and sputters with only 40 psi of fp. this problem is not as bad when the fp is jacked up to about 65.

ls1beater...
What MAF are you running?
The most likely cause (in my experience) is that you have the wrong MAF...

vristang said:

ls1beater...
What MAF are you running?
The most likely cause (in my experience) is that you have the wrong MAF...

Click to expand...

well im running a pmas 75 mm bullet maf for 30s...The other maf is a pro m, i doubt that i have two mafs that are bad one of them is mine and the other one is a friends both set up for 30s, his car made 420 /429 at the wheels with 30s and runs and drives fine. I do have a bit more of a aggressive set up then he does though.

ls1beater4eva said:

ok so what injector would i need for my 12.1 comp 347 since this thread is open? i mite as well ask. the car has a solid lift cam 585/600 242/257 on a 106/114, with cnc canfeild heads, holley systemax intake, pulleys, 1/3/4 lts, 70 mm tbody and 75 mm maf. i have 30s in it now with a 255 intank pump. In order for it to run half way decent i have to have 65 psi of fp at wot

Click to expand...

42's. My 30's are 100% maxed out on my 347

ls1beater4eva said:

well im running a pmas 75 mm bullet maf for 30s...The other maf is a pro m, i doubt that i have two mafs that are bad one of them is mine and the other one is a friends both set up for 30s, his car made 420 /429 at the wheels with 30s and runs and drives fine. I do have a bit more of a aggressive set up then he does though.

Click to expand...

The part you didn't mention is the ecu that the 'calibration' is for.

X3Z ecu takes a different meter than an A9L, even with the same injectors.

Call the manufacturer to confirm the part numbers...