Quote: Originally Posted by tgspeedracer
is there a rule of thumb for what size injector will suport so much hp?
Yes. There is a formula for it. It is as follows:
Injector Flow Rate (cc/min) =
Engine HP x BSFC x 10.5
Number of Injectors x Injector duty cycle
BSFC (Brake Specific Fuel Consumption) varies depending on the type of induction. Here's a breakdown:
* For naturally aspirated engines, estimate BSFC to be 0.4 to 0.5
* For nitrous engines, estimate BSFC to be 0.5 to 0.6
* For forced induction, estimate BSFC to be 0.6 to 0.7
* For rotary engines, estimate BSFC to be 0.6 to 0.7
* For engines running methanol, double the appropriate gasoline BSFC (e.g. a forced induction methanol engine has a BSFC between 1.2 and 1.4)
Injector duty cycle should be around 80%, so where the equation asks for duty cycle, use .8 for the value.
example: 400 Hp Turbocharged 4 cylinder
400(HP)*.6(BSFC)*10.5=2520
4(injectors)*.8(duty cycle)=3.2
2520
3.2 =787 cc injectors
(note: The equation bases calculations off of an assumed fuel pressure of 43.5 psi. Different fuel pressures will result in different needs in injector size.)
Now you must remember that all this is theoretic, so it has margin of error. It's absolutely possible to achieve 400 HP+ on 750cc injectors, and has been proven time and time again. In fact, I believe it's been done with 650 cc injectors, but usually requiring higher duty cycle, and higher fuel pressure. So take all this theory with a grain of salt.
