AFR's Danger zone!?
 

So I'm gonna be installing a AEM failsafe with my turbo this weekend and want the colored LEDs to be a instant indication of AFRs. Can someone point me in the right direction for the ranges of AFRs that are safe and where the danger zone is for normal gasoline. @jamesm @arghx7

Internet tuner rule of thumb is, stay in the 11's (call it Lambda=.81 or less) for gasoline/E10. Now there are things like closed loop delays engine rpms and such that play into that. With E85 you can actually run more timing compared to premium E10 in terms of knock. More timing = lower exhaust temperatures, meaning less fuel is required. As I've pointed out in other threads, when you start advancing the timing you increase cylinder pressure even if the engine doesn't knock.

The problem is, if I tell you to run it leaner and advance the timing, and you do that, I'm an idiot with dangerous advice if something goes wrong. No matter what the root cause of the failure is. And you become an idiot for listening to me.

So I'll throw out a somewhat arbitrary and oversimplified piece of advice and say, stay lambda of =.81 or richer once boost is over 5psi.

agreed, what afr is 'safe' depends greatly on the timing being run. i'd see what you're targeting and set it a half-point leaner than that. there really is no general rule that you can be sure of. you definitely don't want to be over 12:1 in boost though.

This is about how I set mine up:

Red = anything under 9.5:1
Yellow = 9.5:1 to 11.5:1
Green = 11.5:1 to 13:1
Yellow 13:1 to 14.5:1
Red = 14.5:1 to 22:1

If you are in boost and in the green then you are in the go area. If you dip down into the yellow then you are running a little rich. If you are in the red then something is seriously wrong with your tune. If you are the other way, then back out of it ASAP.

i'd have to say 13+:1 under boost isn't green if you ask me... is that what you normally run?

No. I was going off memory, and @Visconti had me tuned to just south of 13:1, but Toni had me tuned to this:

http://brz.ridedomain.com/dyno/fa20club_boost_afr.gif

I meant green was up to 13:1. I will adjust my ranges. They don't let you just set it based on AFR, you have to set it based on where the LEDs fall on the gauge face as well.

12.1 on e85 is what I'm running

ok got ya :). i thought something was off there lol. i usually target 11.2-11.4:1 under boost... seems to make the best power without running what i'd consider to be too lean. i'm sure you can probably get away with leaner/less timing if you wanted to.

that's on e85. it's typical to target ~1 afr point leaner on e85 than on pump gas.

In boost you want to be with in the 11 range. 12.0-12.1 is usually ok but thats starting to get lean. 11.7 would pretty much be dead on perfect

i've found that at around 11.6:1 you need to start pulling timing, particularly at higher rpm. i usually taper down to a richer afr above 7k to keep from having to. i don't tune anything to the ragged edge though... usually pretty conservative. i'd rather have 260whp for 100k miles than have 280whp for 30k :).

Thanks for all the advice, the simple answer seems to be ask my tuner what AFR is being targeted and go from there as it depends what fuel and timing conditions are?

For modern NAs you'll want to see around 12.5. They make more HP on the richer side.

For FI you'll want to see about 11.5-12 at most. Some will claim DI can make peak power at 13:1 FI, but our dynos so far have all shown that you're best at 11.5:1.

Melt down is rare these days with sodium filled valves and better piston metallurgy. But knock threshold under boost is much worse at 12:1 AFR rather than 11-11.5:1. Better a little richer and more timing. DI and all.

Below 12 don't rely on the stock sensor. Shoot for a 12.5 AFR, then subtract 5-10% to get your final fueling. Or get a real wideband. Now with RaceROM 7 support you can tie that right into the ECU and don't really need a failsafe anymore. You can just make a custom Load vs RPM vs AFR map, and then use that for failsafe functionality.

i think you mean shoot for 12.5:1 then add 5-10%.. right? i've never done it that way.. interesting idea. so you dial the whole maf (or ve map) in @ 12.5 and then just go through and add the correction globally? i might have to try that next time :).