Matt M

Horsepower is already a time based measurement of work, so RPM doesn't really matter when you are talking about peak HP potential for a certain injector. Yes you are limited to shorter pulses, but only because you have a lot more of them. The end result is the same. Increased pumping losses would be the only factor causing the need for larger injectors at higher RPMs, and that would be minimal.

OntarioKev

As long as he is making peak HP at a low enough RPM point it wouldn't matter, if he were making peak power at a higher rpm, or wanted to rev to a higher RPM for improved 1/4 mile times, 60s on a turbo LSJ would likely go static and risk a lean spike.

This is assuming stock fuel system, return style with boost referenced fuel pressure would make a big difference on the amount of fuel they can flow.

Kevin

Matt M

This is not correct. If your injectors are maxed at 400whp, it doesn't matter if you make it at 6000 RPM or 7000 RPM.

OntarioKev

But at 7500 or say 8000 the pws required for the airflow may not be possible from 60s as the timeframe for injection is getting fairly small.

Duty cycles rise with RPM, so if you want to rev your engine to say 8000rpm on a turbo LSJ you likely can not do that on 60s on the stock fuel system.

Kevin

Matt M

The duty cycles climb because these motors are flowing more air at high RPMs. The reasons most people aren't making peak power at 8k+ are not an airflow issue. It is usually related to not enough timing advance, insufficient ignition system, weak valvesprings, etc... It still requires the same amount of fuel flow to make 400whp at 6k RPM as it does at 8k RPM.

Yes, the timeframe for the injection pulse is getting shorter, but the number of pulses increases at the same rate. The overall fuel flow potential is the same.

OntarioKev

I guess I am used to the SC setup where we make more boost the higher we are reving the engine, and with the stock setup, there is less fuel available with the higher amount of boost.

I will concede to you that the same Hp requires the same amount of fuel, I just notice a significant increase in IDC as the RPMs go up, and prefer to have a bigger injector then run a high duty cycle at high rpm.

Kevin

Matt M

I agree with what you are pointing out on the supercharged cars. One thing to keep on mind is that once you have passed your peak VE, the motor motor starts to flow less per cycle, yet the blower is trying to move the same amount of air per cycle. The result is more boost which decreases your effective fuel pressure on a fixed fuel pressure system. There is also more parasitic loss which would inevitably decrease your net HP potential relative to the fuel injector size. So in that sense, you are correct about supercharged cars.