24lb injector with stock fuel pump
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Wrong answer: 24lb injectors need a 112 LPH pump.
Copied from the 2007 Ford Racing Performance 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 fl ow 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 fairlyconservative fuel fl ow 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 specifi c 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”
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. End Quote
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 http://users.erols.com/srweiss/ to get the calculators used in these examples.
cenok is family
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jammer84_03
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- Nov 30, 2003
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ditto. i have 24's and stock fuel pump. never had an issue of being lean. and i take it to 6g on a daily basis. subscribing....
89CobraGT
New Member
ohh crap I have 24# injectors and I had a mass air flow calibrated to my injectors but whenever I plugged in my new mass air flow the car ran crappy so i threw the stock on in and it runs ok is this going to cause damage??
Sometimes what you can get away with and what is recommended are two different things. I would rather have the extra capacity and not need it, than need it and not have it.
cenok is family
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jammer84_03
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- Nov 30, 2003
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Maryland Stang
Active Member
The Motorcraft parts book calls for a PFB28 fuel pump for both the H.O. and Cobra. List price is $134.41.
Good stuff, it is pretty obvious that many are running very large fuel pumps for what they have.
cenok is family
15 Year Member
Maryland Stang
Active Member
cenok is family said:
It doesn't say. If you go to a Ford dealership and ask for the stock pump that's the one you'll get.
Paul Perreca
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- Mar 30, 2005
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i had 24# injectors and i never upgraded the fuel pump - i bought it, but ended up sellin the car before i put it in - the car ran good but theres alot more stress on the stock pump and its more likely to fail sooner - but it does work
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