Project Supermoto, Part 2

From frame to game: The build begins

Story by Lance Oliver
Photos by Bill Andrews

May 20 – When we last checked in with Ralph DiSanto, tuner for AMA Supermoto rider Mark Burkhart, a YZ450F motocrosser had been stripped to the frame, and parts of the 450cc engine had been shipped to various shops for tuning work.

Two weeks later, DiSanto is now on a first-name basis with lots of UPS and FedEx delivery drivers, as parts have been flowing in from a variety of suppliers and from the shops that did the work on the engine. Now, it's time to go back to the Cycra factory to begin bolting together the bike that Burkhart will ride in the 2004 season.

Except for a few control cables and the radiators, there's little attached to the frame of the stock motocross bike when DiSanto starts work. First to go into the frame is the reworked engine.

A stock engine puts out about 47 horsepower, which is not bad for a 450cc thumper. But DiSanto is aiming to extract 60 horsepower from the engine before Burkhart lines up on the grid for the first AMA Supermoto round in August.

It takes extensive modifications to hit that goal.

Falicon installed a Knife rod and dynamically balanced the crank. Photo courtesy of Ken Elliott/Falicon

Parts sent to For Dirt Only (FDO). Photo by Ralph DiSanto

Porting and tuning of the five-valve head. Photo by Ralph DiSanto

The crankshaft is removed and sent to Falicon to be rebalanced. What does that mean, exactly?

Falicon has been in the business for a quarter of a century and supplies crankshafts to manufacturers, as well as race teams, so it knows cranks as well as anyone. For a single-cylinder engine like this one, Falicon asks DiSanto to specify the rpm range at which he wants the engine to work its best. Then Falicon will either add or delete weight at certain spots on the crank to make it balanced at that speed.

A new piston from Pro-X and new connecting rod also go into the engine, raising the compression from 12.5:1 to 13.5:1. A new camshaft from Hot Cams replaces the stock part.

With those changes adding up to a faster-revving, higher-performance powerplant, DiSanto will need to make sure it can also breathe better. More gas-air mixture in means more power out.

The five-valve Yamaha head is sent to For Dirt Only, a shop in nearby Johnstown, Ohio, for porting and tuning. Meanwhile, the stock carburetor is rejetted with parts from James Dean. DiSanto said the rejetted carb improves throttle response in the low and middle rpm ranges, and not just top-end power.

Finally, a titanium Yoshimura exhaust reduces weight and adds horsepower by letting the spent mixture flow freely.

With the engine in the frame, it's time to bolt on the new suspension, which will lower the bike 1 3/8 inches at both ends. Thanks to the growing Supermoto expertise among suppliers, this is fairly easy work for DiSanto.

The front upside-down fork on the MXer is a pretty trick piece to begin with (left). It has been sent to PR2 Racing in Butler, Pennsylvania, to be re-valved. It bolts on with a new triple clamp and handlebar from Tag Metals.

At the rear end, the stock shock is replaced with a Penske unit (right), specially valved for Supermoto duty. In addition to the full range of compression and rebound damping adjustments, the Penske shock allows quick ride-height changes. If the bike isn't turning quick enough at a tight track, Burkhart can ask for some additional ride height at the rear.

With parts going on, a Supermoto racer is beginning to take shape. But some of the most crucial elements are yet to come.

Stay tuned for Part 3.

Related story: