Thanks for the link; an interesting read.
And it makes sense... when the guys with big budgets want to go fast, the winning combination generally seems to be bigger and bigger bores (unless there are rule constraints, such as bore spacing, etc.). Look at the bore/stroke of F1 engines.
But bringing all this down out of the stratosphere, to where I can get my
grubby little hands around it... my main considerations are that I'm probably stuck with the deck height (give or take a bit), and what can be obtained for flywheels. Custom lengths in rods and pistons are available, but as the cylinder gets shorter, the heads end up being closer together. While this isn't a real consideration on a 90° V8 car engine, there isn't a lot of room on the 45° Sportster. All the cool stuff in the world doesn't count for a hill of beans if the intake faces of both heads are crammed tight together, and I can't get some sort of intake manifold squeezed between 'em!
Obviously, I understand that ports can be moved. But there is a lot of difference between 'fudging' something 1/8" by grinding and milling and a little epoxy, and 'moving' something a half inch or so. One of these is a lot harder for the guy who's working on the engine in his living room!
The 750 race bikes used different heads that didn't pair the cylinders into a common intake; don't ya' think I wish a set of that stuff would become available at a price I could afford.
There's a set on eBay with a $5000 buy-it-now price. Somehow, I suspect I'll have to settle for Buell or Sportster castings. Which means I'll probably have a stock deck height, or close to it.
Now, the stock 3.500" bore of the 1200cc variant would mean I'd have a stroke of 2.06" or less to hit the 650cc limit. The aftermarket cylinders with 3.81" bores would push the stroke down to 1.739". Now, let's pretend that someone can make flywheels (there'd be almost no meat between the holes for the pins in the flywheels); we've gone from a 3.8XX stroke to a 1.7XX stroke - that connecting rod is going to probably grow at least an inch. Doesn't that get ridiculous at some point?
Anyway, I do appreciate the comments and ideas. If there's going to be some real issue with doing this, I'd rather I found it out on an internet thread, than by spending money on the hard parts and going, "gee, I see this can't EVER fit together".
seduce the attractive... charm the rest