Advanced Fuel Injector Calculator

As per industry standard, all injector flow rates are calculated at a fuel pressure of 43.5 PSI from their manufacturer.

Example: The recommended 0 in/Hg rail pressure for the OEM 24 lbs/hr injectors in the 1993 to 1998 Lincoln Mark VIII is 39.5 psi at the rail. If you need to "bump" the pressure past that to simulate a "larger" injector, a 1:1 adjustable FPR is required. However, the best practice is to size your injectors and fuel system to your HP goals due to it having the potential of creating a higher duty cycle for the commanded fuel delivery, which can cause erratic operations at times.

The stock 140 LPH pump is not really ideal for power adders and you should opt-in for at least a good 190 LPH or larger pump to efficiently add rail pressure without worrying about pump failure. Please don't be one of those folks that run N²O and keep a factory fuel pump.

 

Key Notes:

(A) It is best to use a dyno for actual results for engine horsepower.
(B) BSFC is Brake Specific Fuel Consumption and is usually a number between 0.4 and 0.7 for gasoline engines. This can be estimated, but it is best to determine an actual number on the dyno. If a dyno is not available, the following info can be used as a guide: In other words, how many pounds of fuel is used per hour to make a certain horsepower.

  1. For N/A engines, figure a BSFC to be around 0.4 to 0.5
  2. For N² O engines, figure BSFC to be around 0.5 to 0.6
  3. For Turbo or Supercharged, figure BSFC to be around 0.6 to 0.7
  4. For engines running methanol, double the figured gasoline BSFC (Ex. a forced induction methanol engine has a BSFC between 1.2 and 1.4)
  5. For E85 fed engines, figure BSFC to around 0.8 to 0.9

(C) Injector duty cycle should be 0.8 (80%) or less. Duty Cycles higher than 80% are not recommended.  If maximum injector duty cycle is unknown, simply use 0.8 as a guess.

The best way to utilize this calculator is enter everything in order. The desired HP all the way to the final step with the new injector flow rate figure. It will give you a good idea of where your fuel system stands with what you're trying to do with delivery.

Fuel Injector Minimum Size Calculator
Engine Crank Horse Power (Sec. A):
BSFC (Sec. B Note: 1, 2, 3, 4 and 5):
Number of Same Size Injectors:
Injector duty cycle (Sec. C):
Flow Rate: Lb/Hr     cc/min


It should be noted that the 93-98 Ford DOHC 4.6L 0 in/Hg rail pressure should be figured at 39.5 PSI with a 1:1 FPR. You can math that out below.
(Ex. If using the 39.5 PSI rail pressure at idle, use the scale below to figure the increase to baseline. If using the industry standard 43.5 PSI rail pressure, figure "4" on the scale as the ZERO / baseline.)

Static Fuel Pressure with a 1:1 Pressure Regulator

Fuel Pressure Above 0 in/Hg in the rail with a correctly adjusted regulator at idle.

Rail Pressure with correct 0 in/Hg pressure:


Calculate fuel injector flow rate based on rail pressure in the 8 steps below. We know it is a few things to type but worth it in the long run.

The formula is simple.

Example; New rail pressure ÷ Old rail pressure = a factor difference, √ of that factor difference × current injector size = new flow rate after pressure bump.

New Injector Flow Rate Based on Fuel Rail Pressure

This should be used with either 0 in/Hg for N/A or figure the positive FPR signal value for boosted.

1. Enter the New Fuel Pressure :

2. Enter the Old Fuel Pressure :

3.

This Factor Difference is what you will enter below in step 4:


4. Enter The Factor Difference you got here:



5. The New Factor to use below in step 6 is:

 

To calculate the horsepower capacity of injectors based on their flow rating:

Fuel Injector Maximum HP Capacity Calculator. Should be your final step after everything else is calculated.
Injector flow rate: lb/hr
Number of injectors:
BSFC (Refer to Sec. B):
Fuel Injector Max HP:

*This formula calculates, based on all of the entered values above, the maximum horsepower that the fuel injectors and system in proper working order could support.