Best Air Fuel Ratio at Full Throttle?

For those of you who have dyno'd your WRs. What air fuel ratio did the bike make the best power at?

I'm going to be at a dyno day in a few weeks, and I'd like to edit my tune while its on the dyno. But I need to know what air fuel ratio these bikes like, in order to base my adjustment of off. Also, on the FMF programmer, anyone how much my air fuel ratio will decrease by at fuel throttle for each point I go up?

Thanks!

http://en.wikipedia.org/wiki/Air%E2%80%93fuel_ratio

skrew wrote:

http://en.wikipedia.org/wiki/Air%E2%80%93fuel_ratio

If by that you mean 14.7 you are no doubt incorrect.

From my experience every engine is a little different for peak torque and it will vary across the power band.

My old miata made the best power at 12.8:1 until around 4K, 13.2:1 until 6K, and then 13.0:1 to redline.

That was with a turbo, but the same rules apply. Generally speaking you don't get a perfect mix or a perfect combustion so for peak power all engines will need to be tuned a little rich to ensure that all of the available air is put to use.

It has the added benefit of cooling combustion temps a bit so you can run more advanced timing.

You didn't read that careful enough to find AFR curve. That 14.xx value is only "ideal" between consumption and power. All knows that gasoline engine provide most power with AFR near 12.xx

skrew wrote:

You didn't read that careful enough to find AFR curve. That 14.xx value is only "ideal" between consumption and power. All knows that gasoline engine provide most power with AFR near 12.xx

Wow... didn't bother to read that far. It's very unlike me to look at the text first instead of the pictures :)

Good call though.

It's also probably a good idea to mention that being higher/lower than "ideal" 12.6 isn't a big deal. Lambda sensors vary quite a bit depending on location in the exhaust stream, temperature, humidity, etc.

The "best air/fuel ratio" debate aside..... there's no way to really dial in an FmF programmer for that any way is there?

You've got acceleration mode, and full throttle mode, and cruise mode settings.

But those are too general for getting that detailed.


Now if the OP was using a PCV or even a PCIII I could see a desire to have that information.


But an FmF....

motokid wrote:

The "best air/fuel ratio" debate aside..... there's no way to really dial in an FmF programmer for that any way is there?

You've got acceleration mode, and full throttle mode, and cruise mode settings.

But those are too general for getting that detailed.


Now if the OP was using a PCV or even a PCIII I could see a desire to have that information.


But an FmF....

It's just an offset value from the stock ecu map. So in theory you could shift the entire stock curve to match the AFR you wanted, but likely only in certain areas of the power band.

Honestly I don't think I could justify dyno time unless I had complete control over fuel and spark. Gains would just be too small for the outlay of cash.

I have no idea what these engines like, but I do know gas engines produce the most power while running lean, just before they seize or burn thru a piston. Thats why NOS works!!

Nitrous works because it provides more cool, dense oxygen than air alone (not much different in theory than turbo and supercharging with an intercooler). People run into problems with nitrous because it's cheap and easy to install, but they don't make the required fuel management mods nor do they watch their exhaust gas temperatures.

Now back to our regularly scheduled thread...