Chuck, 2 to 1 on the motor side, and 4.5 to1 on the axle side gives you a 9 to 1 ratio. He would need to be 3.25 to 1 on the final drive side to get 6.5 to 1.

And, Jim, I have just over $1500.00 in my motor on the SMT, and I don't usually get run over,

I just went down and taped mine... 39.5" with 10psi.

I believe the part of the crank that is inside the engine is all the same as long as it's for a vertical shaft, other than the two sizes of upper main bearing journals and the 30 has a shorter throw than the 35 and 38 cranks.  However, Briggs made cranks with about 16 gazillion different pto ends... different lengths, tapered, stepped down, etc. That's why they have so many different part numbers.

I agree with what Ted said! Like I said before, I've seen a lot of wrecks over the years, that never would have happened if the bales would have been 5 or 10 feet off the track.

OK, thanks, Joey. Yup, I'm going to Mechanicsville. See ya there.  

I'm just wanting to complain a little bit. I don't like hay bales around the track. I think they are dangerous. In the years that I've been racing I think I've seen more wrecks from mowers hitting hay bales than from any other reason. I agree that sometimes they are needed in certain places to protect the driver from obstacles around the track, or to protect the spectators from a runaway mower, BUT I think they should be as far away from the race track as possible, instead of right around the edge of the track. On Sunday I was racing in Maryland. I was wide open, just a gettin' it, about half way down the back stretch. I didn't think I was as close to the bales as I was and clipped one with the right rear tire. They sucked me right in and spun me around. I went from wide open to a dead stop in about 10 feet. The bales were tightly packed and pretty heavy (I know, cause I helped put them there!) I stayed on the mower and it stayed on its wheels, but any other mower, other than a Super Mod, and I would have been tumbling and flipping out through the weeds. So, what I'm trying to say is, if you need to have hay bales, or any other type of barrier around your track, try to keep them as far away as possible. It will make it a lot safer for everybody.

The chassis rules appear to be the the same as the Super Mod rules, except for the frame. What if somebody builds one and then in a year or two, they decide they would like to go a little faster and do a little motor work to turn it into a full blown Super Mod? It wouldn't be legal if they had built their own frame. Why not keep the rules the same, except for the engine? That would help out with the local classes and possibly the national classes later on.

Click the link and open the file.  http://www.heymow.com/index.php?topic=12522.0

A 31 ci has a 3.556 bore, so I believe you got a 31... just like Birdman said.

Look under Briggs Flathead, the 4th post down that says Briggs Specs Torq