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Author Topic: What does "dialing in" fuel mean?  (Read 13113 times)
c4andmore
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« Reply #15 on: January 16, 2017, 08:14:40 PM »

Pump gasoline. The octane is irrelevant as far as AFR.  Many race fuels also uses these AFRs while some racing fuels need slightly different AFRs depending on the chemical composition.
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nyet
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« Reply #16 on: January 16, 2017, 09:00:16 PM »

With race gas, you don't need to cool the charge to prevent knock. Target lean best torque (12.2:1 to 12.0:1)

With pump gas, you might need as rich as 10:1 to keep IATs and cyl temps under control, but at the cost of torque (if, hypothetically, you didn't have to pull timing to prevent knock/det).

Also, 10:1 (even 11:1) result in black smoke. It does not indicate your fueling is miscalibrated.

As usual, YMMV. Dyno tuning is the only way to guarantee max power.
« Last Edit: January 16, 2017, 09:02:42 PM by nyet » Logged

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c4andmore
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« Reply #17 on: January 17, 2017, 09:02:43 PM »

My comments assumes that the engine being tuned is using an appropriate octane gasoline for the application. Obviously if a substantially lower octane fuel than required is used then there are all sorts of compromises and running very rich AFRs up to a point will help cool the chamber/valves to mitigate some detonation issues at WOT. Note however that one major auto maker discovered that AFRs richer than 10.6:1 at WOT in their turbo engines induced knock due to the heating of the residual end gases from the excessively rich AFR.

Even with racing fuels the AFR still needs to be well below that of NA engines (~12.5:1 for NA), because of combustion chamber heat build up. After a few seconds at WOT the chamber temp increases rapidly increasing the intake charge temp as the cooing system is unable to remove the excessive heat from the combustion chamber fast enough. The engine can go into thermal run away with leaner AFRs causing detonation even with 100 R+M/2 octane race fuel. That is why IME with WOT engine dyno calibration that ~11.8:1 is the leanest reliable AFR typically used in the low to mid-range RPM range transitioning to ~11.2:1 for upper mid-range to max rpm. These AFR's are for non-oxygenated pump and ~100 R+M/2 octane race fuels - excluding the rocket science 110+ R+M/2 octane type racing fuels.

In boosted engines auto/turbo makers do not tune for SAE Leanest Best Torque (LBT), as is appropriate with an NA engine where it is actually safe and desirable to run at Minimum Ignition for Best Torque (MBT), and LBT. In a boosted application where maximum reliable performance is desired you tune for leanest safe AFR based on the thermal load the engine sees. In short duration (drag racing for instance) you might use LBT on a boosted application but you are asking for serious engine damage when doing so for more than a few seconds at a time.

FWIW, I've never seen black smoke out the exhaust on a properly calibrated engine with a true 11.2:1 AFR at WOT. If you are pulling excessive timing or using excessive fuel to compensate for excessive boost or excessive static compression, etc. then it is very possible that black smoke will result. It would be better to lower the boost/compression ratio as late timing results in burn-down of the intake charge in the exhaust manifolds at higher RPMs causing extreme thermal load to the exhaust valves, ex. manifold, turbos, CATs, etc.

I realize that for years some "tuners" have used excessive fuel and retarded ignition to try and eek out a few more top end HP but it's bad for the engine to do this as mentioned above. The auto makers and turbo companies do not calibrate engines this way as reliable performance is the goal not extremism. Proper dyno tuning will result in maximum reliable power. Extremely low AFRs can create fuel build up in the oil causing premature bearing/cyl./ring wear.

BTW nyet, I have been reading here for some time and I realize that you are a great contributor to the forum and I respect this. Now that I am active on the forum I am sharing my firsthand experience to help the community. There can always be exceptions to the norm or individual situations where there is a need to deviate some from established best practices but the above AFRs have proven reliable in a variety of engines in 400 hour WOT engine dyno durability tests and actual highway operation.

I don't want to see newbies damaging their engines from trying to used excess fuel as a crutch for excessive boost, timing, compression, etc. or engine damage from lean AFRs.
« Last Edit: January 17, 2017, 09:17:21 PM by c4andmore » Logged
nyet
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« Reply #18 on: January 17, 2017, 11:40:19 PM »

FWIW, I've never seen black smoke out the exhaust on a properly calibrated engine with a true 11.2:1 AFR at WOT. If you are pulling excessive timing or using excessive fuel to compensate for excessive boost or excessive static compression, etc. then it is very possible that black smoke will result. It would be better to lower the boost/compression ratio as late timing results in burn-down of the intake charge in the exhaust manifolds at higher RPMs causing extreme thermal load to the exhaust valves, ex. manifold, turbos, CATs, etc.

I realize that for years some "tuners" have used excessive fuel and retarded ignition to try and eek out a few more top end HP but it's bad for the engine to do this as mentioned above.

Don't disagree with any of the above, but unfortunately, most of VAG's turbo line up has extremely high CRs, and there is no avoiding the realities of a 91oct tune on the west coast.

This means 11.5-11.6:1 and a lot of pulled timing, even with gaskets to lower compression... leading to black smoke on occasion at peak torque and single digit timing. In any case, I ran my 2.7t with 100% stock internals for 150k of very hard miles, at 2+x stock torque, many track days etc. with 11.6:1 and enough pulled timing for 91oct (even with lowered CR gaskets) and it eventually gave out (bearings/rods, not heads/valves/exhaust etc), so your warning should not go unheeded. Pay to play, no matter what you build.

Quote
BTW nyet, I have been reading here for some time and I realize that you are a great contributor to the forum and I respect this. Now that I am active on the forum I am sharing my firsthand experience to help the community. There can always be exceptions to the norm or individual situations where there is a need to deviate some from established best practices but the above AFRs have proven reliable in a variety of engines in 400 hour WOT engine dyno durability tests and actual highway operation.

I don't want to see newbies damaging their engines from trying to used excess fuel as a crutch for excessive boost, timing, compression, etc. or engine damage from lean AFRs.

Understood, and your experience and offer to share information is welcomed.
« Last Edit: January 17, 2017, 11:41:58 PM by nyet » Logged

ME7.1 tuning guide (READ FIRST)
ECUx Plot
ME7Sum checksum checker/corrrector for ME7.x

Please do not ask me for tunes. I'm here to help people make their own.

Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience.
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« Reply #19 on: September 27, 2017, 10:30:01 AM »

Don't even feel bad. I never knew what dialing in fuel meant for the longest time.
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golfputtputt
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« Reply #20 on: January 02, 2018, 12:34:39 PM »

very educational, thank you
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