At Stainless' suggestion, I'm going to keep a build diary for this.
Oldest son has an '08 XL that had a lay down with some front end damage so we figured it would be a good time to do an engine build and associated frame mods with the idea of running the bike at Speed Week / USFRA in what is looking like 2025.
New engine started life as a "kinda" SB100 which we picked up as parts. We're keeping the square 4" x 4" bore and stroke.
Came with STD dual carb heads, but testing showed they wouldn't flow more than 250cfm even at .700 lift.
Note the pocketing and lack of squish
The rear cylinder was scored due to a button failure and I wanted longer skirts than stock SB100 pistons so I called Dan at Axtell for taller ductile cylinders.
Since the bolt pattern was open, we decided to modify Milwaukee 8 heads to match Sporty cam geometry. Also since we're designing the engine for 8000 rpm WOT it's a lot easier to move 4 little valves .570 than 2 big valves .700+
Flywheel spread is an issue so when I ordered the rods from Carrillo, I went longer (7.440) and a 1.500 big end- like an XR. But XR rods are narrower so I was able to find a XL width 1.500 crankpin
Stock sportster pin
XR pin
The S&S pin we're using. Drive side is welded