Efficient Engineer

Bonneville Salt Flats Motorcycle Challenge

By Hap DeSimone

Sometime back in the early 2000s, I walked into my friend Dave's motorcycle shop and saw a poster that made an immediate impact on me. It was Denis Manning's advertisement of the BUB Enterprises meet at the Bonneville Salt Flats. What was different this year was the prize was offered for the most efficient motorcycle to complete a run both ways down the salt. In other words, the fastest bike per cubic centimeters (cc) of engine displacement would win.

Any engineer worth his "salt" immediately knows that the smallest engine wins this competition. My best friend Mark and I took on the engineering challenge and began to scrounge parts to build our speedy, small engine motorcycle.

Mark's son had an RC car that donated a 3.5 cc fuel engine. We salvaged my son's 250 DT1C Yamaha dirt bike; the transmission still worked. We hammered the cylinder off of the piston (and unceremoniously let it hang out of the crankcase) while we drove the clutch basket with a set of sprockets and chains from an old 10-speed bike we found out in the back yard.

The R/C car motor drove a centrifugal friction clutch, so we didn't use the clutch lever and cable for that. We figured that we had a good chance at the prize, but we had no idea that we would have to pass a rigid technical inspection.

Motorcycle Challenge The first thing that I did when I dragged the dirt bike out of the weeds was throw away the metal chain guard so we could get at the parts better. The first thing we heard from the Tech Inspector was, "Where's your chain guard?"

The inspection got worse. "NO ignition shut off (it's a glow plug), NO fuel shut off, NO emergency stop switch..." We were doomed. We didn't even have enough fuel to go the three miles each way (two miles just to get to the one mile long traps)! We had to invent most of the technology on the spot and that "spot" was many hundreds of miles from our garage and spare parts bins! We journeyed into a neighboring town with hopes of being able to modify our bike enough to pass tech inspection.

At a thrift store we found a weed whacker that provided a fuel tank and hose. It didn't have any fuel though; we wound up tracking down some model airplane fuel to do the job.

A few friends stopped by the 99 Cent Store and bought a couple of rat traps and a stuffed rat. We removed the cotter pins from some of the rat traps and finagled a handful of them onto one of the traps. They were released by a single cotter pin pulled out by the clutch cable. The trap snapped, throwing a stick against the flywheel of the little model engine, stopping it cold. The same cable was wound around the fuel line, choking it off. We had our ignition shut off, fuel shut off and emergency stop switch.

The AMA racing rules insist on having metallically protected fuel lines. That requirement is usually met by using a rubber fuel line with a metal braid around it. Since we didn't have any metallic fuel cable, we stripped a few feet of braid off the coax of the CB antenna and slid it over the fuel line... voilà, an instant metallic shielded fuel line!

We still needed a chain guard replacement, so we stole the muffler heat shield off our Aerostar, then cut and beat it into shape. It worked great! There is such a thing as a "Rat Bike," meaning that it looks like a piece of junk and is made out of discarded items. I'm not so sure our assembly ascends to that lofty category, but we zip tied the stuffed rat to the bike for good measure!

Finally we were ready to race!

Mark used his battery powered drill to start the motor, but it was rough going. By the time we made our return run, we had drilled a hole in the frame and put a screwdriver (lassoed by a wire so it wouldn't fall onto the track) on board so I could "tune" the carburetor whilst I rode through the traps.

Suddenly it all was going south for me. I just couldn't seem to keep the bike upright. It was losing power BIG TIME! As I rounded the last black pylon at the end of the traps, I lost so much speed, the bike just fell over! I guessed that it was carburetion but when I got up off the salt and looked at the bike, the tires looked like sugared doughnuts. It had been raining a bunch and the tires were wrapped in salt! The dirt bike fenders had generous clearance but not for a ton of salt!

Finally we made it, out of the running for a prize, but we had found our niche in life. It's the best place to go if you are an engineer in need of a project to race! The "Rat Bike" was our first but it inspired two electric motorcycles to follow. They BOTH won their class, becoming National Champions!

Have you tried building an efficient vehicle? Send us your story at [email protected].


Hap DeSimone lives in Santa Barbara, California. He is a retired electrical engineer that has worked as a radio repairmen, TV repairman, Senior Electronics Technician and was a Senior Developmental Engineer for Hughes Aircraft. His interests include designing, building and riding motorcycles, radio design, analog and digital design and instrumentation design. Hap has been a Jameco customer since he was young.