Fuel pressure / Flow rate formula

Daniel Houlton houlster at user1.inficad.com
Thu Nov 12 23:17:18 GMT 1998


What's the formula for figuring out the flow rate of an injector if you
bump up the fuel pressure?  I've found 2 different ones that give *huge*
differences in the result.

The first is from an MSD fuel management catalog/brochure I have.  It
states that 


F2 = sqrt(P2 / P1) * F1


For me, I have a 20 lb injector at 40 psi and I want to check the flow
at a maximum of 70 psi, so

F2 = sqrt(70 / 40) * 20  =  26.4 lbs/hr


Not as much as I had hoped.

I then found a different formula on the RC engineering page 
http://www.rceng.com/technical.htm.  It's almost the same, except that it
uses a strait ratio between the pressures instead the square root of them,
so according to them, I have:


F2 = (70 / 40) * 20  =  35 lbs/hr



This is a very large difference.  Which one is right?


thanks
--Dan




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