AFR Thread
 

So we all know fuel is key to making a boosted stock (or any) bottom end last. So, what AFR are you guys all targeting on your builds, and how much boost are you running?

Ill start. My gauge is calibrated to 14.2 stoich for 10% ethanol. That said, I target 11.2 on my gauge with max 12psi boost up top (6200 rpms). On boost and a 100 shot I target 10.7 AFR on my gauge.

My motor is far from OEM but i am still very conservatively tuned by PatG. I am at about 10.8to 11.0 on 14psi from my little D1SC. We tuned it with the meth pump turned off. So i am sure that it is even richer than that. I only use the meth for cooling. I am not worried about a few extra HP. It has too much now to be useable. I havent been able to get past 3/4 throttle yet.

I will be watching this thread closely. I'm at 7.5 psi with a 4.00 inch pulley on my whipple, but will be dropping to a 3.85 inch really soon. At WOT my A/F is an indicated 10.8-11.0. I have not altered the gauge to correct for ethanol as Dan stated....Is this an issue? Most of the pumps around here state "May contain up to 10% ethanol", but don't say exactly what the amount is. Without knowing exactly, I'm not sure it is even worth messing with. Any thoughts? What is a good rule of thumb for cruise a/f (no boost) and full boost? I was under the assumption at cruise 14.7 was ideal, and under boost anything under 12.0 was acceptable

10.7 and even 11.0 is still very rich. Very safe though, if fuel is and issue I would stretch it out to 11.8 or 9, but no more tham 12.0 under full boost, high rpms, and NOS. If IAT's and EGT's are still good....go further. 11.5 will be my sweet spot for piston cooling and optimum performance.

Stoich for 10% ethanol is 14.2, but if you haven't set your wideband up for that, it's ok. You will read 14.7 stoich even though it will actually be 14.2 if you are running 10% ethanol. Hard to explain. Im sure a tuner can come in here and explain better than i. By my gauge being set up for 14.2 stoich I am seeing exactly what I am getting with the fuel I'm running.

Me being at 11.2 at wot is like a 100% gas engine at 11.7. If your gauge was set up for 100% gas and you were seeing 11.2 you would be rich.

11.5 on wot. 14.7 at cruise 13.5lbs boost

Yes, all depends on the fuel. Need to know the stoich. Then you can determine your afr. It's easier to deal in lambda. Program your stoich into your wide band. Then .85 lambda would be about the correct value at wot N/A 12.5 afr for a stoich of 14.7, which is gas with no ethenol. .85 x 14.7 = 12.495 afr. For FI, a wot .78 lambda would yield about a 11.5 afr. .78 x 14.7 = 11.446 afr.
For E10, gas with 10% ethenol, stoich is about 14.2. Program the wide band for 14.2. So, a lambda of .85 would be .85 x 14.2 = 12.07 afr. .78 x 14.2 = 11.076 afr. So, if you deal in lambda, it doesn't change, but the afr will change depending upon fuel.
If the wide band is solely programmed for 14.7 stoich, then subtract .5 from your afr for E10. Like dan stated.
These are the numbers I shoot for, .85 (E10: 12.0afr) N/A wot and .78 (E10: 11.0afr) spraying.

Also, just got this in the mail yday. Just add tap water and the gas you want to test. The ethenol absorbs the water. Then read the percentage of ethenol at the separation line, between the ethenol/water mix and the gas. Pumps in the area state upto 10% ethenol. Tester indicates 10%.
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VERY good explanation. Thank you.

Also, those of you spraying, don't forget when spraying a bigger shot to richen up due to the AFR of nitrous being 7:1. Our gauges are calibrated in air, but then we give the motor air and nitrous. Many people don't calculate that into the equation. When spraying a boosted motor it becomes even more critical.

I run 11.8 at 12 lbs of boost with meth. This is on a fully forged engine mind you. You need a combination of AFR and timing that will give 0 knock under any condition.

Great info guys, thanks. Now to find the manual that came with my wideband so I can adjust it for Ohio fuel. I'll be sure to adjust my tune based on the new readings. If I am reading all of this info correctly, my car is actually extremely rich at WOT with an indicated 11.0 really being 10.5. This explains why my mpg are a lot less than others with similar setups. I have 0 knock under all driving conditions currently, but sounds like I might be able to lean it out a bit and still be safe and pickup a little power and mpg!

Yes. 0 knock for sure. I always liked to push the timing more than the AFR if I push the line with anything because bad tank of fuel and too much timing = computer pulls timing. Too lean = meltdown.

Just thought I would add this into the mix: I have had a 3.85 inch pulley sitting here for over a month that I hadn't installed. Based on the earlier discussion of my AFR indicating 11, but really being 10.5 I decided to install it today. Changed out the TR6 plugs to ZR1 plugs and installed the pulley. Took it extremely easy watching A/F ratio like a hawk. Too my surprise, I am still indicating 11-11.2 AFR with the smaller pulley. I haven't logged it yet to see what boost I'm hitting, but with the 4 inch pulley I was at 7.5. The pulley should be good for 1.5psi to put me back up to 9 (where the stock 4 inch pulley was before headers/cam). I find it hard to beleive that adding 1.5 pounds of boost seems to be working ok with the tune for 7.5. (atleast as far as A/F is concerned). I want to log K/R before I run it really hard with the new pulley. But so far so good

To the OP, I hope my discussion is relevant enough to the original topic..if not, my apologies.

I'm not positive your indicated 11.0 is 10.5 with your fuel. Set your gauge up for 14.2 stoich and check it again to be sure. It might be but I'd want to be certain.

For the pulley change, I think alot of times as long as the MAF curve and MaP is set up right, a pulley Change won't make a huge difference. Just datalog it and watch for knock retard. If the AFR is good and you get KR, then cut the timing back some.

Guessing E10 in OH? Just remember, the stoich for E10 is lower than 100% gas. So your desired afr on E10 will be a lower value, than straight gas afr. Doesn't necessarily mean your running too rich. Change the stoich on you gauge and see where your at for wot. When people list there afr's, the stoich, type of gas, is needed to be known. If your desired afr for straight gas is 12.5, then for E10 it would be 12.0. It's not really more rich, it's just relative to the stoich. It is the same lamba .85.

Your 11 afr set at 14.7 should be 10.5 for E10. It's not running richer than you think, just different bc of different stoich. Still the same lamda. Wide bands are actually lambda meters that then convert to afr based on your stoich.