Target afr
 

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

11 - 12 at boost

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).

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.

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.

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.

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 ;)

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.

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.

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?

I have also heard that there are two theories for tuning this platform: leaner with less ignition and richer with more ignition. I have herd both sides form experienced tuners. I am not sure which is better but I do plan to test both. One thing i know is that DI brings new changes to the way we tune. I have a well revered tuner friend in the Subaru world who is running 12.5 on his modified 15 WRX with the turbo fa20 DI version. Normal PI turbo engines would have problems with this but he is having good results with leaner AFR. This was on a stock motor too.

I haven't seen anything richer than 0.85 lambda, and suspect this to be a dubious claim, as DI engines run quite a bit leaner under load than port injection engines.

Hotter in this context isn't hotter enough to be bad for valves or exhaust components. We're still talking being in MBT AFRs here.

Stock GT86:
http://imageshack.us/a/img171/1876/abbeystockcar1.jpg

That's really no richer than 0.85.....

By it's very nature, running leaner is hotter. Whether that is safe or not, your choice. Safe by it's very nature is a personal opinion, you may only want it to be safe for 10k, others for 50k. Just because an AFR is "ideal" for making power does not mean that it's the best and safest AFR. Adding fuel aids in cooling and adds a safety net, I doubt there's many tuners running any form of boost that maintain mid 12s

I certainly wouldn't want to be at 12.5:1 at max RPM consistently, but you would. Who's right.... perhaps neither of us.

I cannot comment on boosted but all the NA tunes i have seen for these cars target low12 at leanest and most dipping into 11 at max rpm for knock resistance on our 98 ron fuels which are far inferior to usa 93 fuels and often not even as good as 91 usa.

If i go any leaner you have to remove wads of advance and loose power

Quality an composition of you fuel is going to make a difference.

On E85 can run around mid 12 afr (adjusted to petrol afr scale) at high rpm.and about 10 degrees more anvance than 98 ron

Here's a few basic AFR references, note that NONE say that 12.5:1 or leaner is ideal and richer is unsafe:

http://www.endtuning.com/images/airfuel.jpg

http://www.turbobygarrett.com/turbob...g_rich_vs_lean
http://www.endtuning.com/afr.html
http://www.autospeed.com/cms/article.html?&A=1595 (Note point 3)
http://tunertools.com/articles/AFR-Tuning.asp

Lets not forget, where are you measuring AFRs? Are you taking into account valve overlap?

first ::: FA20A is coolest and best fuel mixed engine i saw it on my life ;)
[ame="https://www.youtube.com/watch?v=zc8aUxBZlsU"]2013 Scion FR-S | D-4S Technology Explained - YouTube[/ame]

2nd ::: AFR should works with engine timing advance
3rd ::: rich AFR with increase(add + to timing )ETA means low power , heat up and bad fuel Eco*
4th ::: lean AFR with decrease (add - to timing ) ETA means boom , poping knocking and then engine died
5th ::: boosting it throws more HP
6th ::: MY OWN boosting Table AFR target and ETA target.

http://i61.tinypic.com/wslqpz.jpg

I haven't seen a stock open loop AFR target table for a toyobaru richer than 0.9 lambda. Most of it stays around stoich. I've also not seen an NA tune for these any lower. Look at the OFT tunes for good examples.

If you're losing power you're out of your MBT plateau, and doing it wrong.

The big point here isn't the hard numbers, it's the concept of MBT as it pertains to AFR. If you want to lower EGTs (which isn't much of a concern with an NA application), richen it up until it starts to lose power and then bring it back some. Add timing until you don't make any more power, bring it back some. Do a happy dance. Go enjoy it.

Conversationally, increasing timing means advancing it, decreasing timing means retarding it.
So we're discussing leaning fueling and retarding timing versus enriching fueling and advancing timing. Is that any clearer?