Datsun Roadster Forum-311s.org

Here we go with the next question. What size injectors would be required to support 200HP? What are the advantages / disadvantages of high / low impediance (is this the correct terminology?) injectors?

Thanks, Mark

See: http://www.megasquirt.info/v22manual/minj.htm

Part way down the page. For 200 hp it lists 29 lb/hr injectors, but there is the tunability factor so you can go higher. If you found some anywhere between ~30-38 lbs/hr should work well.

OR: http://www.sdsefi.com/techffhp.htm
They list a slightly higher minimum. (their #s are for 100% duty cycle, when you should be in the 80-85% range)

If you go too large you will get yourself to a point where you won't be able to tune a good idle because it will still squirt to much fuel at minimum injector opening times.

If you go too small, you will get a good idle and midrange but will lean out at higher rpms and lose power, and with a turbo, quite probably burn something up. An expensive something (piston/valve?).

First you have to set some stakes in the ground. You have to know (or assume) what your system will have.
1. Fuel pressure
2. BSFC of the engine (usually a known factor for your engine, look it up) generally .5 is close for a typical engine

A good rule is *generally speaking* given by this equation:

(injector capacity *given in lbs. per hr*) X (qty of injectors) / (BSFC) = Horsepower

So for your goal of 200 HP:

25 X 4 / .50 = 200 horsepower

Several variables can actually reduce the power you make from a set of injectors. Like how hard the ECU can drive them (duty cycle, opening time, driver type), fuel delivery at WOT, available voltage to the pump at WOT, etc., you know what I mean.

The above equation just tells you what the injectors are *theoretically* capable of.