The idea of an auto clutch in a four stroke in an Oddy is very interesting.
First, a disclaimer: I'm not a big fan of shifting a car. I've never driven a single seater such as a Pilot or similar sized vehicle that requires shifting, but I have driven a couple two seaters that did - Hyabusa powered Coyotes from Desert Dog Off Road. It's cool for about 10 minutes then it becomes a bit of a pain. I'd much rather be able to concentrate on driving and not have the extra thing to worry about.
BUT, I'm USED to CVT type car, so I would probably get used to shifting if that's what I had to do. I ride bikes and shift all the time (well, no where near as much as I did with a two smoke), and it's pretty much a no brainer deal anymore - natural part of riding.
That being said, the auto clutch idea is pretty slick! I had a Rev-Loc in a 2001 YZF that was set up for the desert and it made riding a blast. After riding that machine, one of the first modifications I did when I got my CRF450X was to install a Rekluse auto clutch.
Point and shoot. Shift when needed. I can stop on just about any uphill and then just roll into the throttle and drive right on up. Makes the bike act like a mountain goat.
This sort of setup in an Oddy would probably be a total blast.
If I were to consider a bike power plant, the two that I'd look at would be the CRF450 and the YZF450.
Both of these engines put out 47-49 hp - a real world 45. The CRF has a silky smooth delivery, while the YZ has more of a hit. But you can tame the hit with a fly wheel weight.
The downside to both these engines is lack of e-start. BUT, you could consider a CRF450X or WR450 unit. The CRF450X is new - means they're not going to be as common and will be more money. I've not seen hp numbers in print, but I'd bet 42 is realistic.
The WR's been around and is a damn fine engine. In fact, I'd probably take it over the CRF - the reliability of the WR is excellent, while the CRF is a bit picky about valves - you MUST stay on top of oil changes, maintenance and such.
Both the X and WR have lighting coils and will support a small e-system. There are quite a few companies that offer upgraded stators - 100W x 2 from e-line, as an example. Baja Designs does some killer stuff with both bike's e-systems too.
One thing you would want - especially with the extra weight of the Oddy - would be to throw on the heaviest flywheel you can - either bike.
Wow, now that I think about it - how about the 450 quad engines??? E-start, and don't they have reverse?? Yamaha or Honda - toss up on which one. The tranny on both machines is beefed up to take the extra stress and strain running two fat tires on the ground, versus one skinny knobby, would be worth the look at the quads over the bikes. Yamaha will probably be just slightly more reliable - or not at touchy about lack of maintenance.
Check E-bay and see if you can find a "power pack" for either the YFZ450 or the TRX450- would have all the electronics, carb, exhaust and such - complete setup.
Having had the experience two different auto clutches (Rev-Loc & Rekluse), I can definitely say look at the Rekluse. About half the price, no core exchange, easy to install. It's a very sweet unit.
Contrary to some people's beliefs, an auto clutch does not shorten clutch plate life - if anything, it extends it. It's a function of the way it engages. They engage at a fairly low speed, and they do it in a short, but very controllable time. As long as you don't try to ride in too high of a gear, you'll do great.