Max Piston Diameter

[WhipLash96]

What is the maximum piston diameter that you can get out of an M8 case before case boring is needed?

[mstrobes]

i believe 131 ci

[Don D]

133 with 4.625 crank cast liners, 135" same crank steel liners
4.280 or 4.310

[WhipLash96]

133 with 4.625 crank cast liners, 135" same crank steel liners
4.280 or 4.310

Thanks! I am looking at buying a Softail and put a 131 in it. In your opinion, HD kit is a good way to go or do you think that a perhaps custom built 131 would be better?

[Don D]

We are talking about just a few cubic inches either way and in my experience it is hard to beat, value for dollars spent, a 130" with bored S&S cylinders. It is not that hard or costly to have a very street worthy, long lived, good manners, and no crazy octane requirement 130" that makes 155-165hp. But also has the same in torque and a table top torque curve. If warranty is a concern then plan B, the legal 131 from HD.

[yobtaf103]

Doing 128" on a new Fatboy, pipe choice/performance outcome for your choice will be not so easy ,seen a few set-ups that appear to work, still down to how you ride

[WhipLash96]

Doing 128" on a new Fatboy, pipe choice/performance outcome for your choice will be not so easy ,seen a few set-ups that appear to work, still down to how you ride

Agreed that the pipe choice is going to be key. I do have a friend that builds exhaust systems but I am not sure that I want to use his services. I know that the shop that I use will have the ability to assist in the process. A lot of information to consider.

As far as how i ride, this bike won't be a touring bike. It will be built to haul ass...