Which Injector Rating Should Be Used In The Fuel Calc Table?

[ZBass28]

I have been running the FAST for about a year now and have been using
50# injectors which I had bought through PTE. The injectors were flow
matched and rated between 44.7-44.9.

For the last year I had used the 50# rating in the fuel calc table. Recently I
changed it 45# to more match what they flowed and the car seems to run
better in terms of drivability.

Which rating is the correct one to use for the table?

What effect would dropping the calc to 45# from 50# have on the VE table #s
and/or would the car run richer or leaner from this change? It feels like it is richer
up in the higher rpms.

 

[Red Canyonero]

The ratings PTE has for their injectors are done at 65-75% duty cycle, so you should still use the 50lb/hr rating IMO.

You are altering the fuel injector delivery rating, which will affect the speed density equation. The calculations based on the table values and sensor readings will call for X amount of fuel, when you change the delivery rating the pulsewidth required for that amount of fuel will need to change. In your case, the computer would command a slightly longer pulsewidth across the board (all else remaining equal) as a smaller injector would need to stay open longer than a larger injector to deliver the same amount of fuel.

Also remember that the injector ratings are done at 3 bar (43.5psi), and if you are running fuel pressures greater/less than, it should be taken into account. Small discrepancies (running at 50psi base fuel pressure for example) shouldn't matter all that much, as you will be creating a custom calibration anyways.

Brian Green
89 TTA

 

[ZBass28]

Fuel pressure is somewhere between 42-44psi according to gauge, so that
should be pretty good right there.

If I understood you correctly then with the IPW needing to hold open longer
with the new info I put in then the car would most definitely be running on
the rich side...which is what it feels like up high.

I thought PTE tested them at a higher duty cycle (like 80-90%??), I think it's
written on the baggie the injectors came delivered in.

Thanks Brian,

Tom

 

[vtec4gs]

hello,

how are you checking fuel pressure, with or without vaccum ?

I've noticed this happen with other programmable engine management setups where the change in injector size recalibration increased fuel delivery at top end/heavy load. I found out the culprit was injector response time needed to be changed also, in other to compensate for increased PW at that load/rpm.

IMO, go back to where you had it and increase fuel down low to match the a/f ratios of the new injector size that you tried where you found it to be better. You may have stumbled onto more HP or at leased increased fuel at peak torque when you made this change, menaing the older injector size setting was running lean on low end and just perfect on top end.


Greg

 

[nightdiver]

I got the 75s measured before installing and they all flow~ 66.5
at 43.5 psi and 100 % DC
So why do they call those things 75s.......just curious

 

[TurboJim]

If you bought them from pTE, theyre rated at 43psi at 90%

If you bought them elsewhere, I'd ask whats up...

 

[nightdiver]

I bought them from Mike Lee @ a/r so its PTE