Sftull did you talk to the folks at affordable go carts about the engine, It says on the site they can build a engine for you, I was wondering if they could match the 13 to your needs meaning for mud motor instead of 7000rpms. Wondering if they could put a rev limiter and build the motor more for muscle instead of speed. My other question is why didnt you opt to go with the 23hp vanguard. It is 3 year warrenty with 23hp and weighs 77pounds instead of the 13hp clone weighing 86 pounds? The 23 also has lots of mods that can make it an empressive motor that is mud motor tested. I like the 13 but the 23 sounds like it would get better results.
I did talk to them, but I grew up drag racing so I am pretty confident I can put the parts together. I was also thinking about building it for torque rather than hp. The reason I didn't go with the vanguard is b/c I got a new 16hp clone for $289 with no tax and free shipping. The vanguard will be $700 more....i can build the rest of the surface drive for that.
There's a detailed design process but you'll be right at the upper limits of the 8mm belt. You may need to go to the 14mm but it will take some more numbers to figure that out.
I didn't see a 14mm pitch option on mcmastercarr.