I haven't seen any gains past 12:1, and Bryan@GST hasn't either, but the maximum power AFR range is 10.5-12.8:1, so perhaps there is some hardware combo where mid-12s works better. One possibility that I can rationalize is that with the leaner mixtures, the burn rate slows down and more timing can be added. Are you getting more power simply by going leaner with no other changes to the tune, or does the leaner ratio allow more timing advance? I'm thinking it may also depend on the ethanol content of your fuel. If the ethanol content is lower, then a leaner AFR may make better power because the effective maximum power AFR goes leaner because of the higher gasoline content. I've actually been thinking for quite a while now that the optimum ethanol/gasoline ratio for power may be closer to something like 50/50, especially if a premium grade gasoline or race gas is used for the mixture.

 

If there isn't really a knock threshold with 85%, then more gasoline might be the answer.

 

Yep.

 

The local station had a "snafu" last month and the mix was approx E50.

I ran my personal car on the same tune I had with E85 (after tweaking scaling to get fuel trims and AFR back in order as it richened up almost a full point)

The car did not knock at all, however it felt very lazy and soft. Unfortunatly I didn't have time to put it on the dyno to see if it was making the same power as with E85.

-Bryan

 

What would you guys say the best AFR and rough timing for highest fuel economy would be? (gas AFR)

 

So the best AFR I should be running is only at 12.1 gasoline AFR is that correct? I'm currently running around 12.3-12.4 gasoline AFR on the stock turbo.

 

Try 12:1 and see what you get. Probably won't be more than a few HP difference, so it might be something that needs to be evaluated on a dyno.

 

The only difference that I've seen so far when I moved north of 12.1AFR on my E85 tune is that I got rid of the noise knock that I was getting around 4k-5k rpm. Mrfred what peak timing are you running at now?

 

I just had a new O2 housing installed and had the exhaust mani and hotside ported. Prior to that, I was seeing no power gains beyond 15 deg at 7000 rpm with 220 load (20 psi). I'm experimenting this week with adding more timing past 5500 rpm as I know that many people routinely run 17-19 deg out there (and are not going past MBT).

I'm beginning to think that the leaner AFR is reducing knock noise by slowing the burn rate (takes a little longer for an ethanol molecule to find an oxygen molecule).

 

Interesting theory.

We have seen gains on the leaner side of those AFR mentioned.

We have some full blown double pumps coming in tomorrow. Might be able to get some more testing done.

 

If your getting knock for any reason at 11.5-12.0 A/F "whether it be from noise knock or whatever" and if you lean it out to 12.5 and it goes away... Then why would u even try to run in the 11s? Lean that sh*t out and make power its just common sense to me! Use the E85 to your advantage people!! I don't see why its so complicated and has to get so complicated... I have never seen a car be happy and consistent as far as knock goes in the mid 11s "on a gas AFR" on E85 and i have tuned quite a few E85 cars now with great success including my own car that makes quite a bit of power.

When i 1st started tuning E85 cars the first thing i noticed was that if u tried to tune it to the A/F ratio you would on pump gas all you will get is frustration and knock left and right... Well according to the stock knock sensor and ECU that is I would personally shoot for mid 12s A/F and AT LEAST 12.0 and go from there. I would say thats a good middle of the road. I target my A/F to 12.5 and it has done very well. I have friends etc that have tuned for 13.0 and even seen some leaner with great results and absolutely no damage or negative effects over extended periods of excessive reaming and 1/4 mile passes... street/highway runs etc. I wouldnt go much leaner then low 13s to keep it safe but thats my personal opinion from my own experience. Although i have seen some guys run it at mid 13s... I dont tune my car like that or anyones car im tuning.

Of course there are always going to be variables due to setup and combination of parts. But lets try not to make this thread to complicated to read and understand for people as so many threads turn that way on these forums. I cant tell you how many people have told me that they tried to read through some of the threads on the ECUFlash section about injector scaling etc and by the end of reading were more clueless then they were before they started. heck i have even experienced it myself haha. Too much technical jibber jabber will make the common guy confused Technical information is good.. dont get me wrong. But lets keep it simple to understand and not all try to be the Mr smart scientist if you know what I'm saying Not saying anyone has done it yet... but i can see it going that direction fast. It happens so much on these kind of subjects when its really not needed.

 

Leaner is meaner, however there is no problem being cautious with a newer fuel to the masses.

 

Im currently running 28.5psi for peak boost and my timing is at 21* peak at redline (@20psi), and when I tried 22*-24* I didn't see any drastic changes in power and torque in DLL and JOT Virtual Dyno. I will test this again when I get some dyno time on one of my local tuning shops. When you get the chance, can you PM me the results of your experiment after?

 

Bump for best AFR and relative timing for highest fuel economy.

 

Stock 8/9 turbos I usually see around 20-21* up top depending on mods. This is about 1-2* before MBT most of the time. Some FPgreen equipped Evos will see around this as well.

My personal car I run about 12.3 AFR

Most others I target 11.8-12.2 depending on their intended usage (Street, Drag, Road Course).

For fuel economy at cruise, around town, additional timing helps and making sure scaling and latency is as optimized as possible.