Background:

I’ve been doing some experimenting lately with the tune on my bike (2011 Limited 103”, Jackpot 2-1-2 Header, SE Fatshotz Mufflers w/15 discs, and FuelMoto SE/K&N AC) using my PCV/AutoTune as my tool.

My first goal was to eliminate some residual, minor pinging I was still experiencing on occasion in hot weather. When the bike was new the pinging was very significant - to the point that I was concerned of engine damage. Then I installed all of the Stage 1 stuff and the PCV w/AutoTune and the pinging subsided to a manageable level but was never completely gone. Now it’s completely eliminated. I tested it on a 950 mile trip from LA to Phoenix last week in temperatures up to 100 degrees and not a single hint of pinging was observed.

My average fuel mileage for that trip was 34.2 MPG at average sustained speeds of 80-85 MPH.

Now to the point of this thread…

Yesterday I did an experiment to see what effects my tuning was having on fuel economy. I made four 58.3 mile test runs over the exact same route, at the same speed (cruise set at 75 MPH), judiciously filling the fuel tank to the same level, at the same gas station, using the same pump, at the end of each run. The only difference in the bike for each run was the tune (PCV map). I have three custom maps I have developed over time with cruise range AFRs of 13.4/1, 13.8/1, and 14.2/1. Yesterday I tested the 13.4 and the 14.2 maps to see how they effect fuel economy. I did not test the 13.8 map. I’m simply assuming that the 13.8 map would provide results between the two maps tested.

The first run was with the 14.2 map.
The result was 39.42 MPG (58.3 miles / 1.479 gal).

The second run was with the 13.4 map.* (see note below)
The result was 38.15 MPG (58.3 miles / 1.528 gal).

The third run was with the 13.4 map.
The result was 36.87 MPG (58.3 miles / 1.581 gal).

The fourth run was back to the 14.2 map.
The result was 39.49 MPG (58.3 miles / 1.476 gal).

* Note: I had inadvertently installed the wrong PCV map for the second run. The fuel mixtures were the same but the ignition timing had 1 degree more advance in it so the second run is not an apples-to-apples comparison. Because of my mistake loading the incorrect map I was able to extract another piece of information – the effects of ignition timing on fuel economy.

Also note that the results for the first and fourth runs are nearly identical thereby validating the accuracy of my test process.


In summary, changing the cruise range AFR from 14.2/1 to 13.4/1 resulted in a 2.55 MPG decrease in fuel economy (39.42 to 36.87). That represents an approximate 6.5 % decrease in fuel economy relative to a 2.8 % richening of the AFR, or in ballpark terms a 2.5 % change in fuel economy for a 1 % change in the AFR. I’m sure this ratio is not linear across the entire spectrum but it can be used to get a rough idea of what a proposed change in AFR might do to your fuel economy.

And because of my earlier mistake installing the incorrect map for the test, I can show that removing 1 degree of ignition timing resulted in a 1.28 MPG decrease in fuel economy (38.15 to 36.87). Again, I would not expect this to be linear across the entire spectrum but can be used as a ballpark figure for guidance.

I don’t know if this information is useful to any of you but thought I’d share it nonetheless. I figure if it interests me then there’s probably someone else out there that may be interested too.

 

Good information, I have been playing with my cruise AFR's a little and hadn't done any set structured recordings like this so this is helpful. I changed the cruise from 13.4 up to 14.0 and have been "loosely" recording my mileage and it's very close to yours. i was seeing around 34-35 in combo city/highway with the 13.4 and when I went to 14.0 I am now seeing 38-39.

 

Yes great information thanks for that. In my runs with playing with the AFR's and checking gas milage seem to simulate the same. Nice to have a little rule of thumb to go with.

 

That actually makes sense , and the repeatability was a nice oops too.
I have had 2 electra glide bikes , a 2006 Standard carbed , and the 09 Ultra injected.
I ride pretty conservatively , so my mileage may seem high to some.
The 06 fuel mileage increased by nearly 5 MPG as I jetted it richer from stock.
Stock was around 45 , jetted was nearly 50.
The 09 fuel mileage stock was about 45 MPG , and after adding an intake , mufflers , and a stage 1 download , got 50.5 best , 48-49 most of the time (highway).
The thing that got me interested in the download wasn't the fuel mixture per-say , but the more aggressive timing advance.
Most don't realize what a dramatic change timing can make until it goes too far sdvanced for the particular engine combo.
Anytime you get near a perfect combo , any wrong change can dramatically decrease the efficiency of the tune.
Nice job , good info.
Mick

 

2black I think you always provide good data I enjoy. I have my bike running pretty good I think and have not checked mileage yet but I can tell I can get better mileage out of it. I have been looking hard at fuel maps I have and have developed a tune to try I was thinking I will have to back off timing so I think the data is going to help me rethink my tune.

 

Thanks. I try to do my best to provide accurate and useful information.

 

I am running 14:0 AFR, and get 42 MPG on the highway, 38 to 40 in town. with a stage 1 set up.
If I ride her hard in town it can fall to 34-35 MPG. You do a great job and put out good info thanks.

 

I thought our new bikes had a knock sensor to automatically retard the timing if pinging?

 

Good point. It can be disabled to. But I already know with my current set up I can get Close to 45mpg.

 

They do. But the system can only retard the timing a set number of degrees. I'm not sure what that number is but it's not always enough.