1990hondaHF

I'm wondering if there is a an optimal A/F curve for boosted cars? If not could someone point me in the right direction as to how to tune properly? Thanks.

raene

Usually shoot for mid 12s at medium power ranges. Smoothly move from mid 13s at 0vac to mid-low 12s in boost, and 12.0 at higher boost ranges. You can use fuel to dampen detonation and push some timing back in if you run into issues but that's a bit of a hack and you'll lose power and wreck your oil doing that anyway.

Timing is much more important than air/fuel ratio. But don't bother asking for the best timing, there's no answer. It's entirely case-by-case.

1990hondaHF

Thanks for the info.

Fabian

http://www.megamanual.com/mtabcon.htm

1990hondaHF

x2!

Albuquerquefx

Another thing, each engine will be slightly different. One motor may make best power at 12.2:1 A/FR, another might make best power at 12.7:1 A/FR. For example, my pile-o-crap project car (non-Honda ) loves being around 13.5:1 right around zero manifold pressure, and then generally and linearly drops to about 11.8:1 at full tilt. But after a cam and intake manifold swap, it wanted quite a bit more fuel at zero manifold pressure, but just slightly less at the top end.

Idle is the same way; my car is happiest at around 14:1 idle, I've seen others that are OK with 15:1 and even higher.

1990hondaHF

What is a safe number to start with?

Tony the Tiger

For most setups, stay at 12.0:1 AFR and it will be the optimal range for most turbo Hondas.

1990hondaHF

thank you.

blackeg

i like to run my cars in the 11's under boost with the possible exception of low boost like a few psi ill rock a low 12's.

ive found the difference in hp on the dyno testing out diff afr's to be minimal with afrs between the mid 12s and mid 11's, and i always choose safety over a few more hp. i have yet to blow one up from leaning out in 6 years and at close to 20 different motors between mine and my friends

1990hondaHF

does adding more fuel..say going from 12's to 11's do anything to cylinder temps? Are there any other consequences of a lower(more rich) A/F ratio?...not including worse millage...that one is obvious.

Bailhatch

Thats a good way to tune street cars. There's a reason stock turbo cars don't run in the 12:1s (10-11s usually). There isn't that much extra cooling from all that fuel, but a hard 3rd gear pull with a low tank or something might be expensive. Leaving a little power on the table is the way to go. Especially if the car is going to be driving through different states where the fuels are different.

Bugermass

Tuning AFRs is not only engine setup dependent but also fuel dependent.. When tuning on pump gas with say cast pistons you'd want to keep it a bit richer to keep cylinder temps down a bit. Contrary to popular beliefe, richer mixtures burn faster and use LESS timing.. Leaner mixtures burn slower ( more heat in the cylinder LONGER ) and require MORE timing. With pump gas the difference in power is minimal between 11.5:1 to say 12.5:1 .. So you use richer mixutres to keep cast pistons cooler. Now if your running a built motor with alot of piston to wall clearance you can run much leaner AFRs to get extra HP without sacrificing reliability. The reason PTW clearance is important is because leaner mixtures burn slower and require MORE advance so the heat is in the cylinder LONGER and the piston expands MORE. Also leaner mixtures have less boundry layer of fuel to act as a barrier to the heat, but this has less effect on heat transfer than the difference in duration from having to use more timing. As long as the motor is build properly this isn't a problem and can be done safely. Certain fuels LOVE to run leaner. I run Q16 at 12.8 -13.0 under 30-40 psi of boost with no issues. Going from 11.8 - 12.8 on Q16 I've seen gains of a little over 100HP just from the leaner mix. So its all very setup dependent.. You really just have to know your setup, and know your fuels to be able to safely get the most out of your tune. Going 11.5 is always a good safe bet for any setup if your not 100% sure what your doing.

1990hondaHF

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