Injector Sizing

S

spys gt

Forum Member
How do you know when to upgrade your injectors before putting the engine together?
Does it go by flow?
How much HP will a 24# injector and 30# injector support?

Thanks...
 
Are there any negative effects if your engine only needed say 30lb injectors and you went with 36lb injectors?
 
juicedz said:
Are there any negative effects if your engine only needed say 30lb injectors and you went with 36lb injectors?
Click to expand...
As long as you can tune that extra fuel there isn't a problem. To really answer the question you need to know how many injectors you're talking about (so how many cylinders) and what type of power you're talking about or looking for. For example, in my car right now I have 682cc injectors (about 56lbs/hr) and they're maxed out at 18/19psi. I have 750cc injectors (about 62lbs/hr) waiting to go in which I'll probably go for about 20/21psi but tune to a bit richer air/fuel ratio.

Point is I have a 4 cylinder car so I need more fuel from each injector. I'm assuming you're a V8 guy because 99% of the people on here are, but figured I'd give my $.02 anyhow. On my car 24# injectors would be good for about 150hp to the wheels, haha.
 
Well, I can tell you that my 24#/hr injectors are helping me make 340 RWHp, which is about 400 at the crank. I'm running the injectors at 52psi. I think that they are running about 90% duty cycle.
 
My svo 30's are over 100%DC at 5000 when its cool out(60psi) I would say 30's at 3 bar would be about 430 or so rwhp
 
To be more technical: The max Hp at the crank of a typical NA EFI engine is calculated as:
(injector flow rate) times (# of injectors) times (duty cycle desired) divided by (BFSC - engine brake fuel eff... somethingor other). BFSC (I could have the letters mixed up) is typically between 0.475 and .50...

In my case above: Hp = (27.5#/hr * 8 * .90) / 0.5 = 396 Hp @ crank
 
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