New cam most likely will decrease your mileage. My 03 Heritage 88 ci gets 34-39 mpg on a good day but my stock 98 wideglide 80 ci with carb gets only 36-39 mpg. Mine dropped an average of four miles to the gallon but I have my bikes all tuned rich. The 88 twin cam was tuned rich before the new cams. I don't recommend running an air cooled engine lean.

 

I had an SE air cleaner and thunderheader and SEPST with dyno tune. I added the 255 cams and had it retuned by the same guy and ended up with better fuel mileage.

 

I was kinda thinking that if the engine made more power, you wouldn't have to open the throttle as much, which could contribute to using less fuel. It may somewhat offset the extra fuel that the increased airflow resulting from more valve opening could cause.

 

That can be the case if you dont ride more aggresively than you did with the original setup.

 

The set up with my 02 FXD is a 95" kit and SE 203 cams for low and midrange torque. I realize you are just asking about cams only. Our mileage is close to 48 on the open road holding steady speed, two up riding. Around traffic including traffic lights it will fall to high 30's to low 40's. Depends on how the throttle is being twisted and how hard. The cams would typically allow more charge and more complete burning, maximizing the fuel burn efficiency in the chamber. If your have the funds do the 95" kit in concert with cams, you'll be surprised.

 

I would think that if the new cam timing makes the engine more efficient within the rpm range you generally ride it at, then yes, you'll see some improvement in fuel economy, assuming you don't make too much use of the extra torque/hp.

What I think most don't like to admit is, regardless of the engine build, the rider is still the biggest factor in what kind of fuel economy you're going to get. It's pretty much up to you!

Ride Safe,
Steve R.

 

I did a 95" and S&S 510 cams and saw a significant drop in mileage. I will admit I had a very heavy right wrist at first, but even after the newness wore off and getting back to the daily drive was routine the gas mileage did not improve. I have had nothing but problems, with carb and ignition timing etc.. I had to take my ride to a different shop because the first shop couldn't get the corrections made.

 

Just to add my $0.02!
After my build, see sig, my mileage went up 10%.
Before, 42-46 mpg,(Can.)
After, 48-52 mpg
That's all 2-up.
Added bonus.....
Just twist the throttle!!!!!!

 

with just a cam alone it will not drop that much at all...........If it even drops at all