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Fuel Injector Sizing

How to pick the correct size fuel injectors

Ever had any of these questions:

  • How big should my injectors be?
  • How many lbs per hour is my 650cc injector?
  • How much hp can my stock injectors support?


Fuel Injector Calculator

Crankshaft Horsepower (BHP):

Number of Injectors:

Brake Specific Fuel Consumption Desired:

.45 to .50 for N/A Engines,
.55 TO .60 for Supercharged engines,
.60 to .65 for Turbocharged engines.

Maximum Injector Duty Cycle:

Warning: Duty cycle should not exceed 80% (0.80) for
these calculations.

Fuel System Pressure at Rail (PSI):

Injector Required @ Test Psi

Lbs/Hr CC/Min


Injector Sizing 

If you are a mechanic, I am sure you have swapped many carburetors’. You know what happens when you put too big of a carburetor on a small block Chevy; it runs like crap until the rpm's get up. Same thing will happen with too big fuel injectors. So you have two options, try some different ones until you find the size that works (I would not recommend this, but will work.) The best method is to do a little planning and calculating to determine the best-sized fuel injector for your specific engines fuel requirements and having a good idea of your estimated horsepower.. 

  • To convert cc / min to lbs. / hr. - Divide by 10.5
  • To convert lbs. / hr to cc / min - Multiply by 10.5
  • To convert lbs. / hr to gal. / hr. - Divide by 6
  • To convert cc / min to gal. / hr. - Multiply by .015873