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

 

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

Toby

 

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.

 

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.

 

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

 

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

 

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?

 

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