Optimum injector selection

[Todd Knighton]

khearn at scuacc.scu.edu wrote:
> 
> This is a little rule of thumb that an engineer at
> Bosch told me for estimating injector size (#/hr).
> 
> You must first know the BSFC of you fuel.  Pump gas is
> ~.4 to .5, M85 is about .9. (I don't recall what BSFC stands for,
> but the units are #/(hp*hr)). Then estimate your final engine
> horsepower...it doesn't hurt to be a little optimistic here. However, you
> should take an educated guess.  Finally, multiply that horsepower with the
> BSFC. This gives you the amount of #/hr that your whole engine needs. Divide
> that number by number of cylinders to get the size of injectors (if you're
> doing port injection).
> 
> Ex.                est. hp.= 100
>           no. of cylinders =   4
>                       BSFC =   .5
> 
>         injector size=  (100*.5)/4 ~ 12.5


	Be careful when selecting BSFC's.  Normally aspirated engines work well
with .5 bsfc's but turbo's need a lot more fuel, like 25% more
sometimes.  Which would take you all the way to a .625 or so.  and would
change this now to (100*.625)/4 = 15.625, then taking into account that
you never want to run the things over 80% that would now go to about
19.53, or 56% larger than the initial calc.

Todd Knighton
Protomotive Engineering