Injector Math
CEIJR at aol.com
CEIJR at aol.com
Mon Mar 22 15:37:28 GMT 1999
Math with only two variables? Not near enough giggles.
What you need to do is program your laptop to prompt for input of intake
runner length, diameter, minimum port area, taper, header diameter, primary
length, collector length, static compression ratio, rod length, bore, stroke,
maximum piston speed (in furlongs per fortnight), number of cylinders, number
of valves, four or five temperatures in Kelvin degrees, fuel octane, timing
advance, air cleaner pore size and your age at last birthday. Then, the
program should combine all of those in a multi-step algorithm which returns
the answer of 500 HP, which is what you have been thinking all along. (Then,
have it display to six decimal places and you can market the program as a
laptop engine analyzer.)
FWIW, fuel injector flow isn't directly proportional to rail pressure. It
varies as the square root of the increase, so to get from 50 to 56, you need
to increase pressure about 25%. And that, of course, doesn't match what is
really happening, because it assumes wide open constant injector flow. The
rates of opening and closing are also affected by rail pressure, and the
percentage of total pulse width consumed by opening and closing affects the
average flow, so the actual fuel delivery has to be measured at each rpm and
pulse width if you want an accurate number. Then, of course, you still have to
assume the horsepower before you can decide if the injectors are big enough.
Safest is to go big, just in case your engine really works. Having destroyed
more than one turbo engine with lean mixture at max power output have begun to
suspect that the injector assumption of .55 BSFC may not take into account
enough internal losses or necessary cooling effects when the system is really
working.
Charlie Iliff
More information about the Diy_efi
mailing list