I have a 2012 Sportster 48 with a Zipper's Hammer 88 big torque kit. The upgrade to 88 cubic inches made a huge difference in horsepower and torque. It was suggested by Zippers to change the stock gearing to something else to help the engine reach it's max potential for power and torque. I just want to know if there is anyone here who has done a hi hp engine build and upgraded or changed the gearing? What exactly is entailed when changing the gearing on a bike and what would be a ball park estimate of the cost of such an upgrade? Any advice is appreciated.

 

I've made gearing changes on a couple of my Harleys, but always lowered them from stock. Stock Harleys all come with very high gearing, partly to help them meet EPA noise and exhaust emissions. So by increasing your performance by a big margin as you have, you have made good use of the high stock gearing and that alone could well be enough IMHO. You're probably a very happy chap in any case!

So it isn't clear to me just what Zipper meant. With your engine as it is now you may well have enough power to raise the gearing and hence increase maximum road speed, if you really want your bike to go flat out. If it hits the rev limiter in top gear quickly then that could be a good idea.

There are two ways you can change gearing: swap compensator in the primary; swap the front belt pulley. For the primary you will need a new chain as well (it will need to be longer) and for the rear drive you will need a longer belt. It's simplest to do the belt, as it is easiest and quickest to get at. If you do decide to do this yourself, get the factory service manual first, so you can learn what is involved!

 

You already have a 3.51:1 ratio in 5th. What is your rpm in 5th at 70mph. My calculations put you at about 3200 at 70 mph. I would think that you are at your limit as it is. Why go more? It's a great gear for power transfer with your motor build. If I'm wrong let me know...

 

I agree with both of you. I am happy with the way it is now and feel no need to change anything. They finally cleared it up for me and suggested swapping the front belt pulley but I don't think I will.