1slowbusa

iTrader: (8)

So I had the car at the track last Friday and I am looking over my scans. Run 1 I still had about a quarter or less of 93 in the car with maybe 1 gallon of the Sunoco 260 GT plus. By run 5 I had dumped the rest of the 5 gallons on 260 in the car and I would say the fuel ratio was 90/10 with the 260 being 90%.

So run 1, at WOT my AFR is running around 12.7-13.0. Perfect, dead on. Run 2, it got a little more leaner and by run 5 I was running 13.3-13.8 AFR. I didn't change anything in the tune.

So, that being said, the Sunoco 260 GT Plus Fuel does advertise as being oxygenated. So do you think this is why I my readings went leaner with the race fuel? That's the only thing that changed and that I can think of.

Link to the 260 GT Plus
http://www.sunocoracefuels.com/fuels/compare-fuels?fid=25

93camaro_zzz

iTrader: (13)

The stoichiometric value of that 260GT fuel is less than that of 93, unless you actually have E10 in the car, then it would be pretty close. But to answer your question, yeah if you have an oxygenated fuel, it can make the car run lean.

1slowbusa

iTrader: (8)

Thanks for replying 93Ccamaro_zzz.

I understand the stoich is less than 93. It makes sense it was leaner, just wanted to kind of confirm it by talking to someone else.

I am going to try keep putting the 260GT in and tune for it since the car is only a track car. It will also be better for the car once I start spraying. If i go back to 93, i can just download that tune and im good. The benefits of doing the tuning yourself.

Thanks again.

93camaro_zzz

iTrader: (13)

There ya go.

gametech

iTrader: (1)

I just did the math on that. with the 13.7 stoich of the Sunoco, going from 12.8 on 93 to 13.7 on race gas lines up perfectly with the same amount of fuel in the tune.

1slowbusa

iTrader: (8)

Hi game tech, Can you explain how you come up with that? Thanks

gametech

iTrader: (1)

13.7, which is what Sunoco says is stoich for that fuel, is roughly .93 of stoich for pump gasoline. The AFR 12.8 gas reading on your wideband is about .92 of the 13.7 you registered with the race fuel. This is quick and dirty math, but it is close enough to blame the difference solely on the fuel switch. To get perfectly accurate numbers would require a few more calculations, but the margin for error in the range of readings you provided is already larger than the difference in the "quick" math and the "correct" math.

JakeFusion

iTrader: (7)

This is why you should tune in lambda and not A/F if you plan to swap fuels. Did you change the stoich in your tune? And did you setup your wideband's offset for the new fuel? If you did that then it would still read 14.7 as stoich since it's reading stoich with the proper offset...

gametech

iTrader: (1)

While you are certainly correct, sometimes it is easier to just think of 14.7 as 1 lambda, and refer to the proper tuning window in your head. This is especially true if you mix meth injection, or run a flex fuel tune. If you switch fuels a lot, you could easily forget that you recalibrated a wideband offset, which goes back to the first sentence you wrote about just using lambda instead. Correct or not, however, I know very few people who have their widebands set to output straight lambda readings. It's kind of like metric being better than SAE, but America still resists the conversion.

JakeFusion

iTrader: (7)

Well it's good practice to setup the tune for the fuel being used and the offset of the wideband to read it properly, even if not in lambda. But then once you set it up for lambda, you never have to switch it on the wideband... you just change in the tune. And you know that .87 or whatever is safe for WOT and 1 for idle/cruise.

joecar

The stoich AFR for the Sunoco is richer by 7% than the stoich AFR for the 93...

but his wideband (reporting with respect to stoich of 93) is reporting leaner by 7%... this is because he did not edit the stoich AFR in his tune.

joecar

+1 what Jake said about using lambda...

I set up PE to command lambda 0.86-0.87 and as long as I set the correct stoich AFR (to match the fuel being run) in the tune, I know that PE will be safe (with VE/MAF having been already corrected) for any fuel being run (E0, E10, E15, E85, E100, methanol, propane, LPG, CNG...) (and of course for some of those I would need much bigger injectors).

NicD

iTrader: (7)

I will never get the whole argument of switching everything over to lambda because it's easier and I do this every single day. Yes I know the advantages but I don't care because if you just set your stoich value correctly in the PCM you don't need to change a thing on the wideband which is nice because I'm not going to be changing customers gauges, etc as they may not be familiar with it. Just let it continue to show the gas scale and tune accordingly as it's normal numbers that everybody is used to. Seeing as how the recommended lambdas for all of these fuels pretty much lines up with what you would be seeing for regular gas a/f ratios on a gas scale it doesn't really matter with pump gas, race gas, E85.

93camaro_zzz

iTrader: (13)

I tend to agree. I usually tune everything in gasoline scale anyways. When I am dynoing an e85 car, and I see 11.5:1 at WOT on my gauge, I know I'm good. You just cant forget to convert or something like that if you ever need to in the scanner.

joecar

I know, and I agree (14.7 CL, 12.6 NA, 11.5 other), but my customers tend to confuse the issue trying to reconcile all the AFR's (using the wrong argument/logic).


There are some ECM's that report commanded lambda (do not even emit AFR), and we got some WB's that report lambda, so we make it simple by comparing lambda's.

subeone

iTrader: (5)

ALL widebands report in lambda.

The numbers are spit out in most widebands to be 1.00 lambda=14.7:1 AFR, NO MATTER the fuel.

after all, oxygen sensors detect oxygen content, not HC content.

joecar

Some of the different popular brand widebands assume different value for stoich AFR's.

93camaro_zzz

iTrader: (13)

Partially true. Most widebands report in 0-5V, and what they do with it after that is just a scalar value and an offset value. So even to turn the 0-5V into lambda takes both of these values, just like converting to gasoline scale takes both. AEM widebands can report in lambda value, but even being completely comfortable in tuning with either way, there is just something about the gasoline scale numbers that everyone is more familiar with. If I am doing a pull in a turbo car, 15.0 at WOT tells me to let out of the pull much more than 1.02. Just maybe how my mind operates I guess.

1slowbusa

iTrader: (8)

I just want to thank everyone for their input, I didn't expect so many.

So, I just want to get this straight so there is no confusion and since I have only tune with the 14.63 AFR as stoich. Right now, I am using AFR on my wide band to tune, not lambda. I do this because that's how The Tuning School teaches it and i am used to it.

So, to start, right now I use 14.63 as stoich and 1.142 as my power enrichment EQ ratio. 14.63/1.142=12.81 AFR at wide open throttle.

If I change the Air Fuel Ratio Stoich to 13.7 for the Sunoco Fuel and change my power enrichment EQ Ratio to 1.07 (13.7/1.07=12.8), will I need to change anything else in the tune except for dialing in the VE table and the MAF Calibration table?

Or

Can I still use 14.63 as my stoich and dial in the VE table and MAF table. I have looked at the logs and from my last run at the track, I need to add roughly 6% more fuel to the MAF Calibration table at wide open throttle. Maybe this is the wrong way and just a way to trick the system??

Also keep in mind this is a track only car and does not see the street except for when I load it on the trailer.

Thanks for your input and remember, we are here to learn from each other and not looking for negative input.

NicD

iTrader: (7)

All you do is change the stoich value in the computer for the fuel change, that's it. Don't change PE and continue to use the wideband as normal with standard gas A/F ratios and tune for that 12.81 AFR that you mentioned. Dial in the VE and MAF as normal but they really shouldn't change much if any if it was dialed in before on regular pump gas.