A 500cc hybrid monster By the staff of Dirt Wheels
Yet another fire-breathing, torque-churning monster machine has come to life in the depths of Daryl Rath’s compound. Daryl leaned on his skill and expertise, as well as his expert staff to bring to life a hybrid—a Yamaha YFZ450R endowed with a Suzuki LT500R two-stroke power plant. The aptly named “Rathzilla” was devised to destroy the competition under the control of Rath’s stepson, Jared Weckman. Weckman is an impressive pilot on the Midwest TT racing circuit in the two-stroke Pro-Am class.
Rath Racing is a Minnesota-based company that generates sport ATV equipment, and they have produced many trick and quick racing machines. Welcome to the inner workings of the Rathzilla!
THE BONES OF GLORY
No two hybrid machines are alike, and their origin stories are equally unique. Daryl Rath won a TT championship in 1993 with an LT500-powered Honda TRX250R. Weckman has been around the Rath shop since he was 3 years old. He grew up with race quad and quad racing in his blood and the smell of burning premix in his nostrils. He wanted to build a machine that would relive those glory days of 1993 with a current 500cc two-stroke TT quad.
The search was on. Rath and Weckman were fortunate to find a nice LT500 that already had a Cool Head on the engine. After removing the engine, it was easy to sell the clean LT rolling chassis.
Daryl built the Rathzilla to rise above other two-strokes in the heat of battle. Every part that was chosen, and many were custom created, serves a purpose in the search for power and enhanced performance. They took a 2008 Yamaha YFZ450R and stripped it to its bare bones. From there, frame strengthening was performed, and customized engine mounts were fabricated for the 1990 500cc two-stroke Suzuki engine. The engine mounts are rubber-isolated to soak up some of the harsh vibrations from the engine that would transfer to both the frame and the rider.
The 1990 Suzuki powerplant was in good shape and ready to run on the stock bore. A 39mm PWK carburetor was worked over by LED and installed. Rath created a custom intake, with a K&N air filter, to feed a higher flow of air to the carb and engine. The Rath custom intake included a V-Force reed cage to improve intake performance.
Trackside Performance added a cherry on top with a custom hand-cone exhaust pipe routed on the right side of the bike. An LT500 pipe normally runs on the left side of the bike. The pipe is finished off with a Duncan Racing short silencer. Basically, Rath kept the silencer can but built new internals to suit the LT500 engine and the custom pipe.
Finally, a stock YFZ fuel tank was heated and strategically pushed in to clear the tall two-stroke engine. The tank feeds that sweet two-stroke oil-and-gas mixture to the Rathzilla hybrid’s engine.
TT races run on a smooth track that features both left and right turns and jumps. Like all forms of flat-track racing, the machine set-up is highly specialized. Fortunately, Rath Racing is the nexus for the art form. The freshened and reinforced Rathzilla Yamaha YFZ450 chassis gained Rath A-arms, a front sway bar and a swingarm with a TT linkage.
The Rath swingarm has a Baldwin bearing carrier and a LoneStar Axcaliber Pro racing axle. The Rathzilla also gained Rath billet hubs that swapped the Yamaha to a Honda bolt pattern. The machine was protected for the rough-and-tumble racing with Rath nerf bars, front bumper and rear grab bar.
More TT trickery followed with Motowoz shocks that shorten the travel to 7 inches. Light, spun-aluminum DWT wheels are wrapped with TT-specific Hoosier ATV dirt track tires. The rears are a short 18 inches tall, but 10 inches wide on 10-inch wheels. The fronts are also a stubby 18 inches tall, but are 5.5 inches on 10-inch wheels.
A TRX450R thumb throttle and Honda OEM grips start the controls off. A Works Connection EZ Build clutch perch has a bearing in the pivot and allows a selection of lever ratios designed for each machine. To slow the massive beast down when needed, DP Brake pads were used front and back.
A BREATH OF FIRE
The machine was completed just before one of the final races of the 2020 season. Like all projects, it was a major rush to put all the pieces in place before the race. That included the classic “no time to test” guess during setup and going to race. The constant worry about being off enough to seize the engine is a weight that must be born.
This machine started as a tribute and a literal blast from the past. It may be a blast from the past, but Rath and Weckman report that the Rathzilla is simply a blast in the present as well. Plans are underway to make sure it is a bigger blast in the future. In its first heat race in the two-stroke Pro-Am class, Weckman holeshot but finished third. Having an expert on hand, he asked papa Rath what he was doing wrong. Rath advised Weckman to stop riding the 500cc two-stroke like a small-bore two-stroke. Short-shift the bike and keep the engine in an rpm range where it has traction and doesn’t wear you out.
With sage advice in mind, Weckman holeshot the main and just pulled away for the win! Obviously, this was a perfect result for a new and untested project machine.
Shortly after the race, the Rathzilla was in parts once again. The engine is at LED Performance Engines to have the engine ported and rebuilt using a Rath micro-polished transmission, Hinson clutch and more. The cylinder will remain at the stock bore, with a port and polish of the cylinder performed by LED. The rare Pro Design Cool Head cylinder head that came with the machine increases cooling, so it will stay on the engine.
When the engine is fully up to modern specs, the Rathzilla will be reassembled for plenty more laps on the TT track. Rath feels that if he dialed the chassis in for his weight and track setup, he could lap within a second of a pro 450 four-stroke setup. That is impressive. Modern four-strokes are fast and stunningly capable, and the smooth power is a bonus on a flat-track surface. That this machine with a motor over 30 years old can run those times is impressive. And, of course, there is still that walloping two-stroke power to make the Quadzilla a blast to ride and have fun on.
75 DESIGNS: (763) 439-1289, www.75designs.com
Custom graphics kit: N/A
BALDWIN MOTORSPORTS: (440) 224-2734, www.facebook.com/baldwinmotorsports
Bearing carrier: $234.95
DP BRAKES: www.dp-brakes.com
Brake pads: $41.90
DOUGLAS WHEEL & TIRE: (800) 722-3746, www.dwtracing.com
Rolled bead front: $74.95 ea.
Rolled bead rear: $$85.95
FLY RACING: (208) 319-3079, www.flyracing.com
Aero tapered handlebar: $79.95
FOURWERX CARBON: (262) 501-9696, www.fwcarbon.com
Seat cover: $155
HINSON RACING: (909) 946-2942, www.hinsonracing.com
Billetproof clutch basket: $259.99
HOOSIER TIRE: (574) 784-3152, www.hoosiertire.com
D12 18×5.5-10 front: $103.19 ea.
RD20 18×12-10 rear: $110.01 ea.
K&N FILTERS: (800) 858-3333, www.knfilters.com
LONESTAR RACING: (800) 457-7223, www.lsracing.com
Axcaliber Pro racing axle: $399
MAXIMA RACING OILS: (619) 449-5000, www.maximausa.com
MTL 85W: $9.95
MOTO TASSINARI: (603) 298-6646, www.mototassinari.com
VForce reed cage: $178
MOTOWOZ: (763) 390-9549, www.motowoz.com
Front shocks: TBA, Rear shocks: TBA
PEP PERFORMANCE TUNING: (909) 477-7025
ATV brake lines: TBA
PRO DESIGN: (714) 534-0620, www.prodesignracing.com
ATV kill switch: $34.95
Cool Head: $205
RATH RACING: (320) 234-7223, www.rathracing.com
Sway bar: $439.95
Signature Series nerf bars: $455.95
Grab bar: $82.95
Rear TT link: $325
Custom fuel tank modification: N/A
Custom air intake: $325
Billet hubs w/ Honda bolt pattern: $425
Micro polished transmission: $285
TRACKSIDE PERFORMANCE: (320) 632-6782
Custom ATV exhaust w/Duncan muffler: $850+
WORKS CONNECTION: (530) 642-9488, www.worksconnection.com
EZ Build clutch perch: $151.89 ο