Air/Fuel Ratio

[Corndog]

Anyone know what the air/fuel ratio is on a 2011 stock 96 c.i. engine?

[twistedcherokee]

stoichiometric mixture is 14.7:1, so as close to that as possible.

Toby

[bhaxton]

An engine cant be constantly ran at stoich. There has to be fuel introduced into the exhaust to light off the cat. Most engine OEM's use a strategy called perturbation. This runs a cycle or two lean, and then a couple rich (around 13.5/1). Dont ask me how I know this. I might have to kill you if I tell you.

[speakerfritz]

it depends on the RPM. The ratio is not the same across the entire RPM range. low RPMs the ratio is in the 14.5:1 range. Higher RPMs, the ratios changes to the 13.5:1 area. I saw a map chart recently that did a good job of explaining this. I'll google around and see if I can find it. Here is an example. not the one I was thinking, but it gives you an idea of the ratio change based on rpm.

[mkguitar]

Ratio is dependent on conditions, engine rpm, load etc.

Under acceleration or uphill ( higher load) mixture will be richened, to which extent is determined by the ECM by data from sensors ( o2, RPM, manifold vacuum, temperature, air density etc.)

14.7 is theoretically perfect and will be close that when running steady speed at light load, like cruising at 65 mph on a level road with little headwind.

Running an overall richer mixture ( alot) will contribute to less power, higher emissions, cat problems, oil contamination etc.
Kinda like trying to run your lawn mower with the choke on.

mike

[Corndog]

I thought around 13.1 was supposed to be ideal. Am I all wet?

[Harleypingman]

Originally Posted by Corndog

I thought around 13.1 was supposed to be ideal. Am I all wet?

Yes, you're all wet. As mkguitar explained, there is no one "ideal" AFR. One of the advantages of EFI is it allows a far greater degree of matching AFR to the required conditions. You need lower AFR (more fuel) running up a hill than you do running down a hill. You need lower AFR accelerating from a dead stop and getting up to interstate cruising speed than you do running at a steady speed on a flat highway.

13:1 is extremely rich for virtually any riding condition; and, if you run that regularly you'll probably have a lot of unburned fuel contaminating the oil impairing the oil's lubrication capability.

Another advantage of EFI is the injectior allows the fuel to mist/atomize faster with the intake air compared to carbs which drips fuel into the intake air. So, for a given rpm and load, EFI allows less fuel to be added than a carb due to EFI's more efficient mixing of fuel with a given volume of intake air.

Carl

[Corndog]

When my last two bikes were dyno tuned, the maps show that at all rpms, the tech tried to keep the AFR at 13/1. The maps also said "Max WBC-AFR =18.00" and "100%_005.drf" and "DAFR 13.0:1" What does all this mean?

[kingkingking]

Originally Posted by Corndog

When my last two bikes were dyno tuned, the maps show that at all rpms, the tech tried to keep the AFR at 13/1. The maps also said "Max WBC-AFR =18.00" and "100%_005.drf" and "DAFR 13.0:1" What does all this mean?

I dont claim to be an expert but I would expect that the Max WBC-AFR =18.00 means that the highest AFR the sniffer can measure is 18:1.

The 100%_005.drf is the Dyno Run File - 100% throttle and run number 5.

DAFR is the target AFR?

[kingkingking]

Originally Posted by Harleypingman

13:1 is extremely rich for virtually any riding condition; and, if you run that regularly you'll probably have a lot of unburned fuel contaminating the oil impairing the oil's lubrication capability.


Carl

Naw, you can run 12:1 or even 11:1 at WOT without a drama.