i was wondering if there is a way to calculate the prper injector size for your setup? i was wondering if any of you guys knew....

 

What horsepower are you making to the rear wheels because stock injectors can usually only handle around 340

 

Pulled this from the manual from my DFI for my SC motor ( not installed yet )becuase of the SC boost keeps getting referenced. ( I take no credit for being smart enough to have this memorized or defending it to anyone that wants to challenge the calculations! )

JB

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FUEL INJECTOR SELECTION AND SIZING
When sizing fuel injectors you must keep the following in mind:
1. What is the maximum amount of fuel you need to deliver? This requires knowledge of the break specific fuel consumption of your engine at maximum output, values can be from .39 (lean and efficient) to .69 (inefficient combustion chambers and lots of boost). When working with supercharged engines, remember that you need to 'feed the blower', this means that in order to make i.e. 500 HP at the flywheel, you must not forget that the supercharger may take as much as 100 HP to drive, and this power must be accounted for when figuring out your fuel requirement. Let us look at an example of how to determine the fuel requirement of an engine with the supercharger mentioned above, and a BSFC of approximately .53.

500 HP + 100 HP = 600 HP x .53 BSFC = Fuel requirement of 318 lb/h

2. How many fuel injectors are being used? This is pretty obvious, we need to know the per injector fuel requirement.

318 lb/h divided by 8 injectors = 39.75 lb/h per injector

3. At what RPM are we making this power? This is probably where most people get stuck. Not unless you are being so crude as to run your injectors at 100 % duty cycle, can you make do with injectors sized exactly by the lb/h per injector number. A fuel injector needs a certain amount of time to recover from being engaged between spraying events. It is important to know when your injector fires for this step, but let us assume the injector fires once per engine revolution. The engine speed for our ongoing example will be 7,600 RPM, and we need to know how much time there is between injector events.

60,000 ms (one minute) divided by 7,600 RPM= 7.8947 ms between Top Dead Centers

4. What is the % of duty cycle that can be used at this point? This is determined by the time it takes the injector to close after it has been opened, which is usually somewhere around 1 ms. Here we need to know the ratio between the total amount of time available and what we can actually use.

7.8947 ms - 1ms = 6.8947 ms 6.8947 ms / 7.8947 ms = 0.8733 or 87.33%

5. Injector Size Requirement! Now we have all the info required to select an injector.

Fuel Requirement of 39.75 lb/h divided by the maximum duty cycle of 87.33% = 45.5 lb/h and it looks like 45 lb/h peak and hold injector will fit the bill. By raising the fuel pressure slightly over 43.5 psi to say 47 psi we should have the perfect match.

 

A less specific, more general equation would be: FWHP x .07 = #/hr

Ex: 500 FWHP x .07 = 35#/hr (500 FWHP requires at least 35#/hr injectors)

Or: 42#/.07 = 600 (42#/hr injectors are good for around 600 FWHP)

I'm pretty sure this is only close for NA motors.

 

Damn O_O My SVOs are good up to around 360 then. Makes me feel good that I can throw bolt ons into it w/o having to upgrade my injectors I only did them in the first place because I had them laying around. Great injectors, I recommend them. (Ford put thought into them)

 

Man, i see so many people just guess, i have seen pro shops have somone buy injectors just to tell them the new ones are bad, fugged up.