Stock/Modded Air/Fuel Ratio?

Turboguy

Turboguy

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Hey all,

So I'm just coming over from the GM side where I did a lot of dyno testing/ECU tuning of Corvettes, Grand Nationals, etc. with wideband O2 sensors, so I'm pretty familiar with what factory A/F ratios these cars use. (Stock 2004 Vette Z06 had pig-rich 11.8:1!)

Have any of you measured the stock A/F of an LS, and those of you with tuners and dyno time, what A/F ratio do these cars like for max power? Naturally Aspirated cars usually like around 13.0:1 but haven't seen any LS results and wondering how rich they run as my 2000 LS8's fuel economy isn't great...
 
I brought my XCal with me today. I can do some data logs with my current tune, and then go back to stock and do some more. Whether I am at max power is debatable as I don't have a dyno to show how power changes with A/F changes. I also have nitrous set up on the rich side but bottle is near empty at the moment. The raw data may also be difficult to interpret.
 
It would be interesting to see your logged data, but please don't go switching back to a stock tune just for me (if that's why you're doing it). Just a curious question I thought about.
And "max" power would just be the few thousand RPM during PE in whatever gear is 1:1 or closest (3rd/4th?) and WOT, I would guess, not sure though as I haven't done data logging on an LS yet.

Based on how this thing guzzles gas (even with all new O2s, filters, etc.) seems like a pretty rich factory tune, yours must be very rich with the squeeze!
I remember back to the 150 shot my '05 GTO had...man that was fun...
 
I logged last night but discovered a wideband O2 sensor is needed to do this (which I don't have). I do plan on getting an A/F safety switch for my nitrous (which hopefully can be logged by the XCal) but not sure when I'll get around to installation (I'll post some csv files though once I do). I want to lean it out to a more optimal ratio since I'm leaving a decent chunk of power on the table.

There may be some info on the net about QuikLS' car (which sadly is out of commission now) as I know he did quite a writeup on his wideband install and logging with his XCal.
 
Well, I logged a couple O2 sensor PID's with some WOT pulls with car fully warmed up. I was getting .90 volts. After some research, I believe I am still rich on my tune (could have been left over from spraying at the track and I didn't change the setting back to 0). I'll return it to zero and see if it changes the sensor readings at all.
There may be some way to get a clue on power differences. There is a calculated engine net torque value that I could compare. Currently it said peak was 250 ft-lbs @ 3720 rpm. A new gen 1 engine should be 267 @ 4300 though there's obviously more to the equation than the peak value (my plug gap for spraying is also partially to blame). I can plot a couple curves to compare how changing the fuel mixture changes that value. I think its only a couple percent richer so I don't expect big changes. None of it tells me what the actual ratio is though. Do I assume 14.7:1 wherever I get the most power or does each car vary?
 
14.7 is too lean for an N/A WOT max power setting. Most N/A cars make best power around 13.0:1 (seen it tons on chassis dyno sessions).
supercharged/turbocharged like around mid-low 12s to 11s range, don't know what A/F ratio is best for nitrous but I'll bet it is similar to super/turbo range.

I'd recommend that you get a dedicated wideband as your regular O2s are too narrow band for detailed readings, especially since you have a juice setup. I've heard that a regular O2 sensor's readings swing wildly.

I had an old 2001 Z28 LS1 that I put a FAST (Comp Cams) suction windshield-mount wideband O2 setup into. Can use either one channel or two channel (one or two wideband O2s, if two one in each bank). Only difficult part is cutting/welding bungs into exhaust, then you run wires into cabin and mount unit. Very accurate.

See it here: http://www.fuelairspark.com/Products/FS-'Digital Air/Fuel Meters'-0.aspx

FASTWideband.jpg
 
I just confirmed that by looking at more data. I'll be getting an A/F cutoff switch put in. Looks like 13.2:1 is where I should be. I know there is a shutoff that kills the nitrous at 14.5:1
 
Nice, I've never used that brand but hear it's good.

I hear you, perhaps there's another type of safety switch that would work for you...we did some type of safety switch on the LS2 GTO, think it might have been a low fuel pressure nitrous cutoff. There has to be some type of safety cutoff available with all of the juicemakers out there: NOS, Nitrous Express, etc. You could also hedge your bets with some great unleaded race fuel like VP when you know you'll be on the bottle.

I know nothing about this ECM but a little about aftermarket like FAST with some cool features:
I wonder if a dedicated custom tune and a good tuner would be able to program in a ton of extra fuel for you if because of a problem, the A/F ratio started going lean?

The FAST XFI did that when it sensed fuel pressure dropping, threw a bunch of gas at it to save the engine. Had to do with additional Power Enrichment I think, and lots of the upper right-hand VE cells in main fuel table were rich to start with.

Prob asking alot from a factory ECU but the LS ECU is pretty advanced...I think Atari musta made the ECU in my 1987 Buick!
 
02LincLS said:
This one is less than half the price and comes with a gauge you can mount and a bung: http://www.amazon.com/Innovate-Moto...1QFH2RW/ref=pd_sbs_auto_1/185-7599159-8302061

I asked dynotunenitrous about the one that had the nitrous kill and they don't have it anymore.:( I really don't want to have to look at that gauge when I'm going down the track.
Click to expand...

I ran that gauge for awhile in a previous vehicle and was quite pleased with it. I think it is the best deal on a WB solution out there.
 
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