In running the injector calculators for my new combo it's calling for a 60lb injector at 85% duty cycle or an 80 lb injector at 70% duty cycle. I ordered 60lb injectors, but they ended up sending me 80lb injectors.
Has anyone run a 80lb injector-what was your idle injector pulsewidth? I'm just concerned that the on time will be less than one second. These are rated for one second as smallest on time.

 

Are u running a vacuum assisted fuel pressure regulator?

 

Yes, adjustable on the stock fuel rail. Setting it at 43.5lb with no vacuum. I understand that with vacuum on it drops the fuel pressure thereby flow rate of the injector-ust was worried that it would be tough to get a 80lb fuel injector at idle to over 1 second pulse width. The biggest I ran before were 48lb injectors.

 

So what’s the FP at idle? Any mods to the motor?

 

It's apart right now-Pistons came apart with more boost. M&R engines did not put 2618 pistons in that I paid for! M&R is long gone now after a lot of shoddy work. (Using Pettis Performance for short block maching his time)I don't remember the idle fuel pressure right off-just that it pulled 13 inch vacuum at idle. Engine as in my sig-going from the Paxton SN2000 to the only other SC with eo numbers-the procharger P600b, so going from 6lbs boost to 12plus.

Just came across this calculator that also gives what the idle pulse width would be even for batch fire.Thought it may help other folk.
https://www.rbracing-rsr.com/calcinjpulse.html
So per this the 80lb injectors will still be above 1 millisecond at idle.

 

With 80 lb/hr injectors in double-fire mode (running E0-E10 fuel) you can expect the idle pw to be around 0.70-0.75 ms (or even less, depending upon rpm).

Here's a log with 60 lb/hr injectors idling at 700 rpm (and ~1700 rpm) on 93 pump gas with artificially increased load via retarded timing and early cooling fan activation: https://datazap.me/u/tequilaboy/warm...1715-2528-3846

80s will be rich everywhere below an LV8 of ~80 counts or so. The INT will be reset when the min pw limit is in effect, but you may have a little wiggle room here (down to around 1.6 ms or so).

 

Good enough-I'll be exchanging them for the 60lb. thanks.

 

I think that you're way overestimating your injector needs. Here's a P600b car with (my old) Lucas 42 lb/hr injectors (not my car, btw) on California fuel as far as I'm aware.

https://datazap.me/u/tequilaboy/160-...rk=311-213-141

Same car, another example event (but 2 years prior): https://datazap.me/u/tequilaboy/6800...rk=857-845-841

If you already have 48 lb/hr injectors, why not stick with them until that you are sure that you require more fuel? If I still had the 42s, I would go back to them if/when pulling the plenum again.

Another example of 60s on the dyno: Injector duty cycle < 60% at 480 rwhp (dynojet): https://datazap.me/u/tequilaboy/dyno...46-422-435-436

 

I appreciate the info. I do have a question. I saw in your logs it's mass airflow-is this with a FMU to raise the fuel pressure?

 

No FMU. Stock FPR only. Fuel pressure was around 50 psi (and likely falling due to single 255 lph in-tank pump struggling to keep up with demand).

At one point in time I had ~54 psi using a nickel for a shim under the regulator lid, but this has long since been removed in favor of greater flow at lower pressure.