I have a question on the injector pulsewidth numbers in 730 ecm and primarily code $59 but also applies to $8D and any other code on 730 I believe as they all do calculations the same/similar. Correct me if I'm wrong.

I am wondering if you can use the injector pulsewidth displayed in the datastream to estimate HP based on injector duty cycles produced, and so far it SEEMS legit but my new setup seems to be off to me, but I cant tell.

Some examples.... My car last year went 140mph at around 3600 lbs estimated. I had 80 lbs injectors. From my logs I had an injector pw of 8.91ms at ~5500 rpm. From all the threads I read on batch fire, injectors fire one per revolution, and theres 2 fires per engine 4-stroke cycle.

So cycle duty would be base pw * rpm / 600. Or use online calcs and double it. I get almost 82% cycle duty.
The injector sizing calculations for 80lb injectors at 82% cycle duty put me at 800-820 which I consider dead on. Same resutl on the dyno run on a stingy mustang dyno that is known to read very low compared to others in our area. Its an AWD type. 9.7 pw at 5400-5600 where my converter hovered but it was pig rich... Either way it made 690whp which should be closer to 750 anywhere else or higher, so thats almost 850hp on motor thru a TH400 assuming 20% losses or so....


So it seems you can work the numbers out....however here is my dilema...

I have 115 lbs injectors now and at 43-44 psi fuel pressure. I changed heads and cam to something huge and now pull to well over 6500 but only been to 6200 in a second gear pull on the street at only 11 psi boost and running rich.

I have a base pulse width now of 8.45 at 6150 rpm.... granted its rich at mid lower 10's air fuel but leaning out will make more power and drop the pw number but change bsfc I believe... Either way as it stands, 8.45 ms is calculating to 86% duty cycle on 115 lb injectors.....

If you run this in an injector sizer, i'm getting between 1100-1200 hp.... Now the car feels very fast but I cant think this setup is THAT high in hp on only 11 psi and that rich. Even if it drops to 7.45 after i lean it out, thats saying 1050-1100hp still.

Could it be right?? I need track and dyno time sooon.

 

You can do what you are regarding injector PW. Although need to take into account the injector compensation and the BSFC.

A rough guess on the injector compensation is to subtract a milli-second from the reported PW. For BSFC, .55 is typical on a boosted engine. Will be higher on one running too rich.

> I have a base pulse width now of 8.45 at 6150 rpm....
> granted its rich at mid lower 10's air fuel

Using 7.45 PW @ 6150 RPM is 76% DC, figure on .65 BSFC

115 #/hr * 8 * .76 / .65 = 1075 HP

That may not be too far off.

RBob.

 

Wow. It honestly does not feel like 1000+ hp and its hooking up on my old street tires that the milder combo used to blew to pieces but that car had loads more torque down low due to cam and heads being tiny. Idk maybe its a smoother hp curve that gradually applies the power. I am on 19" mickey drag radials now and on 11 psi it will hook first gear rolls and they feel quick but i figured i'd spin tire. Time to dyno or track it for sure.