Looking here and there on the web I find different opinions about the optimal AFR (NA engines):
12.8 at torque peak
13.0 at HP peak
12.5 for auto X-ing
A local tuner uses 13.2-13.5
...

Nice numbers, but wo made a test?

I'd like to see a dyno graph of the same car with different AFR (like 11.0 - 11.5... up to 13.5)

Thanks!

Stefano

 

A lot of people like to throw around a/f. The fact of the matter is that different motors like different a/f (to a extent).

Find where your motor wants to be. Make sure you have no exhaust leaks and have a upstream wideband.

BTW, if the motor is tuned correctly, it does not matter what racing you are doing.

 

we'll the optimum af/r for the best combustion differs bassed on compresion,hp,driveability,and fuel used.look at gas the perfect ar/f ratio is 14.8/1,diesel is 14.6/1,and alchol is 5.1/1.i believe these numbers are correct i will double check my figures.so u can use those numbers to tune from the closer u are to those numbers the more power and torque u will have.though it will not run for long before u blow the engine so the richer u run the engine the safer the tune on your car and more reliable the engine will be.u will also have to take timming into consideration.

 

how do I find it out?
I have a WB just before the passanger cat.

 

Those numbers are the Stoichiometric. Meaning the ratio where least to none of harmful gases admitted. It has nothing to do with power, fuel mileage, etc. Just emissions.

Fuel is used as control (of knock) and heat control. Thats why there is no perfect a/f for every motor, only a starting point.

You will have to tune it on the dyno. Tune it to the richer side (12.8~), tune the timing. After or during tuning the timing you should pull the plugs (or just the hottest cylinders, 5 and 7) at peak torque and check to see how the motor is doing. If it is good, slowly lean it out and check them again.

 

Wow, this is "advanced tech" huh...


He just said he has a wideband, why does he have to use the dyno?

I prefer street tuning.

 

Street tuning is great for tuning in real world conidtions. But you can not see a power difference in changes you make. You can tune with logging the time, and comparing time to other pulls. But the data is limited and half-*** if you ask me.

If the car is a street car, I street tune it, then dyno tune it. Race cars, I dyno tune them, then trim the tune to the weather conditions.

 

14,7 is the Stoichiometric.13-13,5 is where the fuel burns fastest but depends on what fuel blend you have and the engine is less likey to detonate badly

91 oct is not like 91oct from another oil company,the composition of the fuels can be very diffrent so it depends on the engine used

 

This is the point! (And that's why I started this thread).
How much will I loose/gain going for example from 12 - 12.5 - 13 - 13.5
If it's 20 HP I'll maybe make some measurement.
If it's 2.341...HP I'll leave it.
Right now I'm at 12.5 from 3000 rpm up to the rev limit.

 

hehe,

No one can tell you the amount of power you will gain. No one will know for sure. You will have to dyno tune it, so see there.

Sorry if that sounds harsh, but it is the truth.

 

Thats not so true. Since the advent of oil pipelines fuel at every oil company ends up being roughly the same. When you ship 10,000 gallons of oil down a pipeline you don't put 10,000 gallons in then wait for it all to make its way down. You give them 10,000 gallons at the source and they just pull 10,000 gallons out at the destination. The only real difference between 91 oct at one company and 91 oct at another is tank/pump quality (is the tank full of rust or water?) and additives (Techron)

 

There are alot of varibles with each motor that will affect your final A/F point. I've had setups that made the most torque and power at 12.7-12.9 while other setups really like 13.3-13.6. I think alot of it has to due with the quench of the cyclinder and the design of the combustion chamber on the particular head you are using. Same with timing, as I've got variances from 25-27 degrees to setups that end up 30-31.

 

I started to agree with your and then you tossed in running the engine closer to optimum would blow up.....

Why can NASCAR run those engines wide *** open for 500 LAPs at 15:1 or MORE A/f ratios. They arent rich I will tell you that.

 

What about plugs? THey are a HUGE factor on what you can run for AF ratios.

 

I'd not look to professional racing (NASCAR) for the tune you want in your car... unless you've got a crew handy to tear the motor down after each race.

I like the topic, though, and I'm presently logging quite a bit of data on my turbo car... I have variable methanol (Alkycontrol) that was set up with tuning on the dyno. Lately, I've been running a mild hill in third gear to completely "street load" the car while using different set points for methanol pump speed. As expected, more methanol = richer AFR... but what's interesting is that as I turn down the methanol the car seems to pick up power. Setting 1 is at 50% on the Alky dial, with WOT AFR running about 11.5; setting 2 is at 25% and WOT AFR is running around 12. I'll do some more runs (with accelerometer logging) to confirm the SOTP readings. I knew that going leaner could result in some more power, but I did not expect it to be very noticeable. Could be that I'm fooling myself, though. More in a couple of days.

 

Each individual car will make best power at its own particular AFR, this is especially true for LS1's. Some make best power at 12.5, some at 12.8, and some at 13 and slightly higher. If your VE/MAf tables are dead on then you can easily change your WOT AFR by just doing a 30 second change to your PE table, that way you can quickly see what AFR works best for you on a dyno.

Damn this thread is retarded too. The question posted was ok but some of the responses are just plain dumb.

 

smartest tuner I know once said:

Keep AFR safe (as in no-knock) and make the power with spark.

Don't worry about AFR beyond just keeping it in an acceptable range, concentrate your efforts on spark timing.

 

LS1 work a little different, you cant control power by spark alone, many of these motors will make peak power at a certain spark advance and wont make any more power and wont knock any with more advance.

Power can be varied on these engines by the AFR.

 

Over here a dyno run costs around $300 so I won't be able to determinate an optimum AFR nor an optimum timing (I'm too cheap...)

My engine is actually supercharged and timing and AFR are different that what we are discussing here. To tune this setup I spent an afternoon on a dyno ($$$) and find out that in a certain range of AFR and timing there are no power changes. I went from 17* to 21* and from 12:1 to 13:1 and saw no changes at all. But maybe this is something typical of FI engines... The only thing that really helped is my WI setup. the colder charge air resulted in a nice +30 RWHP.
That was with a stock A4 tranny, in 3rd and unlocker TCC. I never went back on the dyno after the T56 installation.


Right now the blower belt is off and I was trying to get the best out of this sub-optimal setup. That's why I asked about power and AFR.

The belt is off because the SQ Vortech blower doesn't like cold starts and over here it's still too cold (SQ has helical gears with tight tolerances - Vortech specifies a min. start up temperature)

Thanks guys for your interesting comments! Keep posting

 

No,each fuel has it´s own ups and down based on composition f.ex anti and pro-knock,evaporazion and volatility

Fuel is a complex blend