Determining What Injector Size to Get

[UltraMagneticAL]

Injectors are an integral part of building your motor, whether you plan on going turbo or even a full NA buildup. Your engine will only produce as much power as your injectors and fuel system will allow it. Here's a little guide to help you determine what injector sizes to get. Remember, injectors normally come in standardized sizes, so round up to the nearest available size (custom injectors can be made, but those can run a pretty penny)

Here's the formula:

Injector Size (lbs/hr)= (Crank HP x BSFC) /(total number of injectors x duty cycle )

The typical duty cycle is 0.85 for NA motors, and between 0.90 to 1.00 for nitrous or FI applications. The Brake Specific Fuel Consumption (BSFC) is the amount of energy that can be extracted given the amount of fuel delivered to the engine. your optimal BSFC is as follows:

Professional racing engine 0.40
High compression engine 0.50
Low compression engine 0.60
Turbo/Super charged engine 0.65

Since most manufacturer rate their injectors by cubic centimeters per minute, you have to convert from lbs/hr to cc/min by using this formula:

lbs/hr x 10.5 = cc/min

On an end note, you will also need a fuel pump that will accomodate the higher flow rate of the injector that you choose....but we'll save that topic for another thread

Happy tuning!

[92LX]

wow, kind of random post, but thanks for posting information, instead of a question, that's a nice change of pace. But yes, this is a great formula that I use all the time at the shop, and so many people ask me this question all the time. So great post!

- Nathan

[UltraMagneticAL]

Originally posted by 92LX
wow, kind of random post, but thanks for posting information, instead of a question, that's a nice change of pace. But yes, this is a great formula that I use all the time at the shop, and so many people ask me this question all the time. So great post!

- Nathan

i usually try to add a tech article every so often....i've written a few already :

[LostSolVTEC]

here's a very informative site on injector sizing for honda's (mainly if you are going forced induction but if ur going for a wicked N/A setup i don't see why this wouldn't hold the same

http://www.evans-tuning.com/viewtopic.php?t=4

[MortsAccord]

Stealth 316 - Injector Duty Cycle Calculation

[EnJoiThaRex]

i posted a post jus like that a while ago determing injector size..yours is slightly more detailed...good job