Fuel question

[DRK]

I'm working out fuel load for injectors on a turbo V8 I'm working on. Similar combos make almost 200lbft more then HP.
When plugging numbers into the formula to to figure injector size do you use the higher value in this case torque or do you always use HP like the formula calls for?

said formulas

http://www.rceng.com/technical.aspx

[The Shaolin]

HP out is directly related to how much fuel you put in. Definitely use horsepower.

[WhatsADSM]

I'm working out fuel load for injectors on a turbo V8 I'm working on. Similar combos make almost 200lbft more then HP.
When plugging numbers into the formula to to figure injector size do you use the higher value in this case torque or do you always use HP like the formula calls for?

said formulas

http://www.rceng.com/technical.aspx

Horsepower.

Horsepower is a function of time (torque* speed), and the amount an injector can spray is also based on time/engine speed.

Imagine you make 500 ft-lbs at 2000 rpm. That equates to ~190 hp. The injector has a total of ( (1 / (2000/60)) * 2 ) = 60 milliseconds of time to spray

Now lets say you make the same 500ft-lbs at 8000 rpm. That equates to ~760 hp. The injector has a total of ( (1 / (8000/60)) * 2 ) = 15 milliseconds of time to spray

So.. since the engine is ingesting the same amount of air per cycle in both cases (torque is the same), the injector has 1/4th the amount of time to spray it for the high rpm example. To maintain the same AFR/BSFC you would need an injector 4 times larger for the high rpm / high horsepower example.



HP out is directly related to how much fuel you put in. Definitely use horsepower.
Well sort of. You can't just spray more fuel in and make more power. It ultimately boils down to to horsepower = amount of air/fuel mixture an engine can ingest per time.
Spraying more fuel in is typically easy, its improving the air flow that is the "hard" part.

[DRK]

Thanks. It should make peak torque around 3500-3800 and hp about 5200-5500 so the spread isn't that far, I guess I'm just over thinking it.

[DurtyKurty]

HP out is directly related to how much fuel you put in. Definitely use horsepower.



Well sort of. You can't just spray more fuel in and make more power. It ultimately boils down to to horsepower = amount of air/fuel mixture an engine can ingest per time.
Spraying more fuel in is typically easy, its improving the air flow that is the "hard" part.

I think he was trying to say that there is a direct relationship between fuel in and HP out where as I don't think you can say that between fuel in and Torque out. Hence, use HP not torque.

I think....?

[WhatsADSM]

I think he was trying to say that there is a direct relationship between fuel in and HP out where as I don't think you can say that between fuel in and Torque out. Hence, use HP not torque.

I think....?

In that case it is a little over simplified but true.

[The Shaolin]

Lol. Yep. KISS, right?