Another dumb fuel pressure question.

[ViolatorTA]

Looking through the stock tunes I have DL'd I was comparing 02 TA IFR's to 02 Vette IFR's. Now as far as a know and with all the replacement part numbers, both use the same injectors and both are rated at the same fuel pressure. What I noticed was a difference in IFR values, though minimal, they are different.

So my question is. If flow rates are determined by fuel pressure and rated flow, why would these be different through GM cals? Could it be that this was part of GM's detuning of the F-Body to keep HP down from the near identical LS1 in the Vette? Could this actually skew the figures of IFR spreadsheets out there? ok...3 questions

I ask mainly because no matter what combination of numbers I put into the spreadsheet that are possible for my injectors, be it 43.5 psi/58 psi or measured 61psi along with manufacture's rated lbs at 43.5 or 58, my 30kpa MAP row in logs stays extremely rich even with a nice smoothed VE table. I have even tried sspddmn's VE with -5/+5% differences in entire table. Figured his would be safe since cam is almost the same and got the same results just a little rich across the board from 800-3600rpms.

Came someone shed light on my non-experience. Just trying to increase that learning curve.

[vatman02]

just my .02. may be it is because of the cams being a bit different one has different fueling needs perhaps this is why GM used such a small injector that they are barely big enough to run a stock motor @ 80% duty cycle it is more dificult to control the injectors at such low map values. i was never able to dial in my 60's at low map pressures afr would be 10.9:1 no matter what i did that wont pass the sniffer so i opted for smaller ones

[joecar]

Looking through the stock tunes I have DL'd I was comparing 02 TA IFR's to 02 Vette IFR's. Now as far as a know and with all the replacement part numbers, both use the same injectors and both are rated at the same fuel pressure. What I noticed was a difference in IFR values, though minimal, they are different.

So my question is. If flow rates are determined by fuel pressure and rated flow, why would these be different through GM cals? Could it be that this was part of GM's detuning of the F-Body to keep HP down from the near identical LS1 in the Vette? Could this actually skew the figures of IFR spreadsheets out there? ...

Can you post the two IFR tables (paste the values into a reply) identifying which one is the ZO6 and which is the TA...

[ViolatorTA]

I'll get them up as soon as I return. It's not a Z06, it's just a base Vette compared to a TA which is what made me question it more. Z06 I may think differently.

[dfe1]

Injector flow rate is only part of the equation. Take a look at B3701- Pulse Width Voltage Adjustment. The values for Corvette and Camaro are different, so it stands to reason that the IFR values are also different. I think the problem you're having is an effect of the cam. Volumetric efficiency is so low at low rpm that you have to come way back on fuel.

[ViolatorTA]

I think you are correct. My last log shows every single cell from 30kpa down in fuel trim cell #21 regardless of rpm. What would be the best approach to set the VE table at for 15 to 30kpa?

[dfe1]

I think you are correct. My last log shows every single cell from 30kpa down in fuel trim cell #21 regardless of rpm. What would be the best approach to set the VE table at for 15 to 30kpa?

I've always found that the best approach is to "listen" to the engine. If it says it's too rich, it is too rich-- keep reducing the data in the appropriate VE cells until the air/fuel ratio is where it should be (I assume you're using a wide band). I'm running a 232/236 cam and the VE table takes a sharp dive below 2000 rpm and below 35 kPa. It's not particularly pretty at the lower end, but AFRs are within 1% of commanded everywhere. Are you running open loop?

[ViolatorTA]

Yes. Running open loop with WB. I begin to worry about going too low in those cells in fear of hurting something and having a false reading.

[vatman02]

I've always found that the best approach is to "listen" to the engine. If it says it's too rich, it is too rich-- keep reducing the data in the appropriate VE cells until the air/fuel ratio is where it should be (I assume you're using a wide band). I'm running a 232/236 cam and the VE table takes a sharp dive below 2000 rpm and below 35 kPa. It's not particularly pretty at the lower end, but AFRs are within 1% of commanded everywhere. Are you running open loop?

i tried this with my 60#ers i had the low map/rpm areas down to 10 and it didnt change a thing it still ran at 10.9:1 i hope i wont have the same problem with my new 42's

[dfe1]

Yes. Running open loop with WB. I begin to worry about going too low in those cells in fear of hurting something and having a false reading.

It really shouldn't be a problem as long as logged pulse width is longer than minimum pulse width. Also, if you get more aggressive with DFCO, those areas of the VE map won't be an issue because in most cases, fuel will be shut off.