Target afr

[Derka]

Good morning guys. I've searched and found some info. But some if it is conflicting. I know there are a ton of variables, but if you could pick a number. What would your target afr be on a supercharged frs on about 10lbs at wot.

I know it's a noob question, I'm not tuning my car, just trying to keep a safe eye on the wideband. Thanks!

[steve99]

Originally Posted by Derka

Good morning guys. I've searched and found some info. But some if it is conflicting. I know there are a ton of variables, but if you could pick a number. What would your target afr be on a supercharged frs on about 10lbs at wot.

I know it's a noob question, I'm not tuning my car, just trying to keep a safe eye on the wideband. Thanks!

probably best to post this in the forced induction thread,

best to ask your tuner what afr they are targeting or look in your tunes ol fuel table

or talk to @King Tut think he has one of those aem wideband guages

[aagun]

11 - 12 at boost

[burdickjp]

0.85 lambda (12.5 AFR) is usually the bottom end of MBT, aka maximum brake torque.
I aim for 0.9 lambda (13.25 AFR), which tends to be dead center of MBT.
Top end of MBT is usually 0.95 lambda (14.0 AFR).

[Kodename47]

Originally Posted by bur****jp

I aim for 0.9 lambda (13.25 AFR), which tends to be dead center of MBT.

Even on this engine? AND supercharged???

[cdrazic93]

http://www.afrplus.com/AFRplus-unit-functionality.asp

[burdickjp]

Originally Posted by Kodename47

Even on this engine? AND supercharged???

It is more a matter of chemistry and thermodynamics than mechanics.

Most of the reason people go richer is to compensate for knock and then try to edge out more power. The power you make in that manner is fragile at best, and catastrophic at worst. Cars tuned this way are temperamental and unpredictable.

In this case conservative tuning isn't running richer, it's running MBT and the appropriate ignition timing to suit.

[jester04]

Originally Posted by bur****jp

It is more a matter of chemistry and thermodynamics than mechanics.

Most of the reason people go richer is to compensate for knock and then try to edge out more power. The power you make in that manner is fragile at best, and catastrophic at worst. Cars tuned this way are temperamental and unpredictable.

In this case conservative tuning isn't running richer, it's running MBT and the appropriate ignition timing to suit.

This is not always the case there are afr ratios that will produce the best power theoretically but on a boosted engine the cylinder needs to be cooled somehow. And timing and fuel determine how hot the cylinder will run and how high pressures will be so don't misinform people about afr's without looking at the specific setup the car is running.

Best advice here ask your tuner.

[yomny]

I think based on what my tuner set me to 11.1-11.7, i'm at 8psi. I'm sure there are variables and other things i'm not getting into because i simply dont know but to answer the OP's question.

[Kodename47]

Originally Posted by bur****jp

It is more a matter of chemistry and thermodynamics than mechanics.

Most of the reason people go richer is to compensate for knock and then try to edge out more power. The power you make in that manner is fragile at best, and catastrophic at worst. Cars tuned this way are temperamental and unpredictable.

In this case conservative tuning isn't running richer, it's running MBT and the appropriate ignition timing to suit.

Really? You must be one of the only sources I've heard to tune like that. Purely tuning to 12.5:1 or leaner just to produce best AFR produced torque.
I'll also note here that finding MBT is actually done by changing ignition timing and not the AFR, not that AFR doesn't have an impact.

Why do you think that running slightly richer but with more timing makes it more fragile or temperamental? You could argue that running some of the AFR range you specified at high RPM would cause too much heat that could damage components and almost certainly would kill cats. Surely the answer is you want the ideal middle ground, not sticking to an AFR as not all engines or setups are that theoretically perfect

[burdickjp]

There's a torque plateau for ignition timing and air/fuel mixture. So there's a similar process for finding best AFR as there is for best timing. The plateau is broader and flatter for AFR.
You'll note I didn't set hard bounds for MBT. it's something you find empirically.

[King Tut]

He is right about finding the best AFR and MBT, but tuners generally run richer not to make more power, but to provide more protection. Most tuners will target from 11:1 to 12.5:1 for a forced induction application.

[burdickjp]

Originally Posted by King Tut

He is right about finding the best AFR and MBT, but tuners generally run richer not to make more power, but to provide more protection. Most tuners will target from 11:1 to 12.5:1 for a forced induction application.

It's the same thing. They're trying to run more advance by adding fuel. Less fuel and less advance is healthier.

[Kodename47]

Originally Posted by bur****jp

It's the same thing.

No it's not. Running richer keeps things cooler, which has it's own purpose. I'm not sure how you equate running hotter is healthier?? Less fuel AND less ignition advance = hot EGTs, which over a length of time isn't likely to be good for valves or exhaust components.

It might be worth noting that the OEM tunes this car richer than you suggest, would you consider that unhealthy?