INjector Guide

[Hen]

Morten Wrote:That calculator is missing one important thing: max. rpm

Reason is that when the rpm increases the time available for the injector to spray the needed gasoline is decreasing. Hence a engine with max output at 9000rpm needs injectors 50% bigger then an engine with max output at 6000rpm to support the same amount of horsepower (at same dutycycle).

I would think the calculator is based on a "normal" rpm of 6-7000, but it does not state anything about it.

Just a little something to keep in mind when choosing injectors.. :wink:

This is actually incorrect. Power output and fuel consumption are closely linked, but the RPM has nothing to do with it.

So if two cars have the same injectors and fuel pressure regulator and one produces 200hp at 5000rpm and the other produces 200hp at 9500rpm then their max injector duty cycle should be the same.

Sure at high RPM, you have a smaller time to inject per stroke, but you have more strokes per second, so hence a greater number of injection pulses per second.

Hen

[Morten]

Hen Wrote:This is actually incorrect. Power output and fuel consumption are closely linked, but the RPM has nothing to do with it.

So if two cars have the same injectors and fuel pressure regulator and one produces 200hp at 5000rpm and the other produces 200hp at 9500rpm then their max injector duty cycle should be the same.

Sure at high RPM, you have a smaller time to inject per stroke, but you have more strokes per second, so hence a greater number of injection pulses per second.

Hen

Good point! It seems I spoke before really thinking this completely through.. by bad

However, in real life it would actually be something in between due to injector lag times taking a larger and larger percentage of the available time as the revs rise..