Is 14:1 Air Fuel Ratio 'Unsafe' for E85 Tunes?

[slaughter.mode]

I am trying to find a thread/post or data that is relevant to this but my current Flex Fuel tuner is adamant that the air fuel ratio *must* remain in a 12:1 (or richer) ratio for the S55 platform for any long-pull racing and anything leaner could potentially end in catastrophic damage. The logs are showing me the lambda target AF:R is only 13.8:1 so unless there's some sort of DME correction, I'm guessing it's not even 12:1 like they said.

My Full E85 (non Flex) tune runs at around 14.5:1 but it runs really, really well. I found somewhere on the net a long time ago that this is safe for full E85 tunes.

I can't seem to find anything relevant to this topic or my googling skills have completely abandoned me. Anyone have any feedback on this? Thank you.

[mike@x-ph.com]

These cars tend to run lean, post your logs for an opinion on whether your map is safe or not.

[slaughter.mode]

E85 map logs:

https://datazap.me/u/nate/e85-v30?log=0&data=7-28

[mike@x-ph.com]

Originally Posted by f82.959

E85 map logs:

https://datazap.me/u/nate/e85-v30?log=0&data=7-28

Which tuner and map are you using?

AFR looks fine, but you have

1- ignition timing drops
2- overboost issues
3-turbos are running at 90% capacity

[slaughter.mode]

Originally Posted by mike@x-ph.com

Which tuner and map are you using?

AFR looks fine, but you have

1- ignition timing drops
2- overboost issues
3-turbos are running at 90% capacity

Yeah probably the 15k worn out E85 abused F8S plugs and the 100k old coils (both have been changed). Cary Jordan did the tune, I think he did a fantastic job considering the variables I gave him to work with. It runs great with all the minor kinks ironed out. Not sure about over-boost issues? That's a new term to me.

[mike@x-ph.com]

Originally Posted by f82.959

Yeah probably the 15k worn out E85 abused F8S plugs and the 100k old coils (both have been changed). Cary Jordan did the tune, I think he did a fantastic job considering the variables I gave him to work with. It runs great with all the minor kinks ironed out. Not sure about over-boost issues? That's a new term to me.

Cary is an excellent tuner, he did my F8x M4. If he says it's good, then it's good.

Im not a tuner; I'm just giving my opinion based on my limited knowledge.

Looking at the log, you are constantly above the target boost set by your map. That's what I mean by overboost. Ideally, you want to be precisely on the target, but in the real world, you should be a lower than the target but as close as possible to it

[slaughter.mode]

Originally Posted by mike@x-ph.com

Cary is an excellent tuner, he did my F8x M4. If he says it's good, then it's good.

Im not a tuner; I'm just giving my opinion based on my limited knowledge.

Looking at the log, you are constantly above the target boost set by your map. That's what I mean by overboost. Ideally, you want to be precisely on the target, but in the real world, you should be a lower than the target but as close as possible to it

Gotcha. Yeah I really blame MHD for a lot of the weirdness but he is absolutely a master at his craft. His tuning methodology compared to my other tuner with the same platform is completely different as well but he knows what he's looking for. Thanks for the feedback.

[chetrickerman]

Safe seems to be subjective in this market. People tend to assume that just because everyone does it, that makes it safe. There are well known rich best torque and lean best torque AFR targets, which regardless of direct injection or port injection, still apply. The main reason you can get away with a leaner AFR when using direct injection is because the atomization of the fuel in the combustion chamber during the compression stroke reduces the temperature of the air charge far more than when using port injection.

A homogeneous 14:1 AFR even on E85 doesn't leave much room in terms of a safety margin. You want the extra fuel in the charge to remove excess heat and it helps make flame propagation more stable.

A stratified charge with a 14:1 AFR can be safe, because the air/fuel is proper mixed in the small "bubble" and it only burns in that localized place of the combustion chamber. A stratified charge is usually used during idle and cruise where more efficiency is desired.

[TopJimmy]

Chet lays in with the knowledge!

[slaughter.mode]

In contrast if anyone's interested, these are my latest logs for my Flex tune, where the target AFR is in the 12:1 ballpark. It makes about 60 less whp and for some reason still misfires in the high RPM range with high ethanol content (above 75%) but runs max power around a E50 blend. I'm guessing it's dumping way more fuel too because I actually get less MPG on with this map at E50 than I do with my monster Cary tune with full E85.

This is with E50:

https://datazap.me/u/nate/flexfuel-v...0&data=5-17-27

[bloke79]

I posted the same question about a month ago (link: https://f80.bimmerpost.com/forums/sh....php?t=1910501 )

I was only able to get back on the dyno last night post implementing PTS’s recommendations. Unfortunately, no dice. Still lean.

[flipm3]

As chetrickerman stated, it's very subjective.

I am personally not a big fan of running an AFR on the leaner spectrum, since the focus of my build is mainly for the road course. Instead of a quick 10-11sec 1/4mi pass, it is seeing heavy load constantly for near 20-30min. I requested, from my tuner, an AFR that would provide good consistent power, cooling characteristics, and safety margin. We intentionally tested a leaner AFR and it really didn't provide a worthwhile benefit to run the risk.

I am currently running custom hybrid turbos, full E85, EU5 injectors, stock cooling system (motor and charged air system). My high power map is hitting 25.5psi, 17.5º ign, and 12.3-12.5:1 AFR. No misfires. Very consistent. 680whp 625wtq. Chugs fuel real quick at the track, LOL. On tighter, low speed tracks, I do run a lower power map, limiting to 20psi.