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[icy]

looking to get a few more mile from a tank of fuel. I keep hearing that baker does a .80 overdrive kit and i also hear of people changing the overall gearing in the primary. I have done the 124" S&S LC motor already. but she REALLY likes her fuel at 75 (approx 32-3300 rpm) and thats where im looking to save a few rpms.  Anyone have suggestions? or what to stay away from? Im not really interested in changing the whole trans unless i get a deal i cant say no to (next to free!!) but i may entertain the idea of doing some work inside, but only if its worth it. i hear harleys six speed is basically a 5 speed with another gear thrown in, having a final ratio of 1:1.

[HD Street Performance]

With the Harley / Jims 6 speed you will lower those rpms by ~475 @ a .86 OD. It is a good box and goes in your case with just one minor change. Depending on the year model of your bike you may consider changing to o2 sensors and closed loop retaining the Delphi ECU and updating the tune file to the later versions. Depending on the year model this can be easy or not very easy. Closed loop control in the cruise range when tuned properly can help mileage considerably. That said just a good tune with the pre-closed loop Delphi system can help when done properly.

[grc]

Harley gets the overdrive affect on the late model Cruise Drive six speeds by changing the primary ratio.  As you noted, the top gear ratio is 1:1.  They basically copied what Baker had done previously with their DD6 transmission, which also has a 1:1 sixth gear and a different primary ratio.  Baker also has their original overdrive transmission that uses the stock primary and either a 0.86:1 or 0.80:1 overdrive sixth gear ratio.  Harley also offered a SE six speed overdrive trans for the '06 and earlier big Twins.

If you decide to stick with the five speed trans and just change the primary or the final drive (trans output sprocket to rear wheel sprocket) ratio's, you may find that method makes first gear too tall, especially if you ride fully loaded or tow a trailer.  Some of the six speed offerings, like Baker's, can be accomplished using the stock trans housing and just changing out the gearset.  That option was also available for the SE six speed, but I have no idea if that's even still available other than as used parts.

No simple answer, and you may wind up spending a lot of money and see very little real affect.  For instance, spending a couple grand to save 1 or 2 mpg isn't going to be cost effective, no matter how you look at it.  The faster you go, the more affect total drag has on fuel economy.  Aerodynamic drag doesn't increase with speed at a one to one ratio.  Roughly speaking, doubling speed will increase drag by four times.

How was your engine tuned?  That can make as much or more difference than a ratio change.  If the tune is set up quite rich in that particular load and rpm range, a simple change in the tune might provide as much benefit as a several thousand dollar transmission change.

Jerry

[HD Street Performance]

I would totally agree with Jerry
Cruising down the road unless the bike is very heavily loaded or in a large headwind it should get in the neighborhood of 42mpg and more to be had without getting too lean.

BTW the gear set is available 33102-03A (01-06 Touring) $2100. 1-5 gears are similar to stock with a .89 OD. This would only drop you 350 rpm. A lot to spend for such a small drop. With a 124 if it were mine I would gear up the primary or change the trans pulley to a 33T (3.05:1 or thereabouts) and call it done then concentrate on the tune. My buddy and I have converted back to 2002 Delphi bikes to closed loop and it is feasible and value added in my opinion.

[garya1]

X3 for checking the tune in the rpm range and modifying AFR there. As usual, Jerry looks beyond the answer the OP wants and gives the best answer.

I would also ask what mileage you are getting at your cruising range?

Is this a new 124 install? If so, I would think a lot of your MPG is eaten up in zero to 80 quick throttle twists!

It would be almost impossible for me to NOT want to feel that added torque every time I merged, changed lanes, passed someone...........noticed the time, notice the song on the stereo, you get the idea.

On the other hand, you can afford a nice new 124LC.......... as I recall Baker makes three different 1st gear ratio choices for their O.D. 6 with 0.086 6th. This would give you the lowered cruise rpm AND a lower 1st gear option for  two-up or towing. This is not the sensible option from a value perspective.

Any changes made in gearing are a trade off.  When you lower the engine RPM for a given speed/gear you also give up some acceleration at the speed/gear. For my preference 75 mph at 3200 rpm is just about perfect. Most would disagree and want a lower RPM like you suggest.

[SDCVO]

For a couple of years I have read about people getting in the 40's for MPG and could never understand why I always ran in the low 30's even though I did it on 3 different motors. I ride by myself 90% of the time and with a couple of buddies the rest but never in big groups before. A couple of months ago I went for a ride with around 10 people including a couple that were new riders. The pace was slower than I was used to  but was still a great ride. When I filled up that day, lo and behold I got 43 MPG. Bottom line is you have to decide what is more important to you. Same thing goes for tires BTW.

[tdkkart]

2 words.....

SLOW DOWN

My '15 110" will get 43mpg fully loaded 2-up if I keep it at 60mph or less.
The very same bike, same load and conditions, yielded 34mpg at 80mph for 110mi on the Kansas turnpike.
The factory map in this bike puts the cruise fuel ratio at 14.4 AFR(.988 Lambda).

I will agree with the others though. Get yourself a proper tune to make sure where your fuel mix is AT YOUR CRUISE SPEED.
VERY likely that it's too rich for optimum cruise mileage.
 

[Royalroadie]

For a couple of years I have read about people getting in the 40's for MPG and could never understand why I always ran in the low 30's even though I did it on 3 different motors. I ride by myself 90% of the time and with a couple of buddies the rest but never in big groups before. A couple of months ago I went for a ride with around 10 people including a couple that were new riders. The pace was slower than I was used to  but was still a great ride. When I filled up that day, lo and behold I got 43 MPG. Bottom line is you have to decide what is more important to you. Same thing goes for tires BTW.

I like you have always gotten poor gas mileage.  I went for a ride with a group at the westcoast gtg and for the first time I got 44 MPG! I finally realized it was me, not the bike, that was the problem.   I really could care less about the mileage, it's all about the smileage, that I am after.  It's nice to know that my bike can get in the mid forties so I know it is running properly, but after that I could care less.

[twinotter]

 I'd have to agree with the others about having the AFR checked at the noted RPM's your running. 3200 is a noted sweet spot for an S&S T124, at least it sure is for my T124HC!  Mines got a G carb, in an 01 Dyna, final gear ratio is 2.88/1. It turns 3000rpm @ 80 mph. Much lighter bike, the engine is incredibly smooth right there, and has seen 47 mpg regularly. It stays smooth up thru 3500rpm, but too high into the "ticket zone"!! hehe  Your bike should be able to reach 40 mpg loaded up at 3200 without any real issues. AFR around 14/1 should be adequate at those rpms under cruise.
I've seen where newer bikes with the taller gearing get less mileage in 6th than 5th, I'd be hesitant to spend money on a 6 speed with the possibility of making it worse. jm2cw fwiw Buffalo