SR Archive: Muzzys ZX-7 Drag Bike

Muzzys return to the sprints from 1996

What happens when you stick a 750 Superbike engine in a dragracing chassis? Muzzys Kawasaki and Prostar are about to find out.
What happens when you stick a 750 Superbike engine in a dragracing chassis? Muzzys Kawasaki and Prostar are about to find out.Photography by Lance Holst

Before Robert Muzzy became Rob Muzzy Superbike Champion, he hung out at the digs. Straight-line acceleration measured in hundredths of a second over a quarter of a mile. No warm-up laps, no heroic last-turn stuffs, no victory wheelies. Horsepower and hook were all that mattered. And the Muz was good.

Muzzys Superbikes usually wear trick, adjustable triple clamps, but stock trees work fine for dragstrip fun. The speedometer and idiot lights were unbolted, leaving only the tach and its 14,400-rpm re
Muzzys Superbikes usually wear trick, adjustable triple clamps, but stock trees work fine for dragstrip fun. The speedometer and idiot lights were unbolted, leaving only the tach and its 14,400-rpm redline sharing space with a digital coolant-temperature gauge.Photography by Lance Holst

Fast-forward to 1995 and Prostar’s desire for a 750 Pro Superbike class. Muzzys R&D in Bend, Oregon, now firmly ensconced at the top of Superbike roadracing, got a call from Prostar’s main honcho, Scooter Kizer. “Will you build a Superbike dragracer to be displayed at the Prostar final in Gainesville?” Rob’s dragracing roots made the decision for him. Plans were drawn up and six weeks later the bike fired for the first time. Additional support and inspiration came in the form of Muzzys main engine man, Gary Medley, who now builds all the team’s Superbike engines but was once axle-deep in dragracing, running a 750 Kawasaki triple and even Elmer Trett’s machines a few times. Doug Meyer, in charge of Marketing and Product Development for Muzzys, once held the IDBA Ultrastock record and ran a lightweight Kawi KZ900 with big ponies years ago. These two heard dragracing and, with the help of Muzzys Dave Messimer, began work. Here’s the first look at Muzzys return to the sprints.

Prostar rules are aimed at keeping a lid on spending, and this stock wheel and single brake are as per regulations, as is the DOT-legal Dunlop. Don’t worry about the weight of stock wheels, because al
Prostar rules are aimed at keeping a lid on spending, and this stock wheel and single brake are as per regulations, as is the DOT-legal Dunlop. Don’t worry about the weight of stock wheels, because all Pro Superbikes must have a combined bike and rider weight of at least 600 pounds.Photography by Lance Holst

Medley's Motor
Gary Medley bolted together a Daytona-spec mill with a close-ratio roadracing tranny for a baseline on what a Superbike engine could do in a dragracing chassis. Prostar's Pro Superbike rules mirror AMA Superbike and mandate stock displacement, but everything in the engine has been touched and massaged, including a Rob Muzzy porting job, degreed cams, lightweight valve train and about 13.8:1 of compression, though no one's really talking. Knowledgeable guessers estimate 150 ponies, and anyone who saw Scott Russell at Daytona knows the kick of this Kawi. The first run posted a strong 142.40-mph trap speed, though Medley wasn't happy with the 9.88-second ET.

Daytona focuses on top speed, and this engine wasn’t providing enough midrange grunt off the line to really load the wheelie bar, even when leaving at 12,000 rpm. The tall first gear and peaky delivery combined to produce a bog unless the clutch was slipped mercilessly. This bike still wore its starter, alternator, stock wheels and a wheelie bar—the extra weight, compared with a Superbike, didn’t help the launch. Medley slapped on a 15-tooth front sprocket and 45-tooth rear sprocket (the shortest gearing in the truck), juggled the jetting (changing both needle and main jet), but short of re-degreeing the cams and changing first gear, a quick 60-foot time wasn’t going to happen. We couldn’t “throw away” the clutch and ride the wheelie bar because the engine wasn’t tuned to produce enough midrange to keep the bike from bogging. The clutch stayed strong and the tranny shifted beautifully, but we ended the day with a promising yet disappointing 9.69-second run at 139.71 mph, with a best 60-foot time of 1.549 seconds on a winterized racetrack that was far from ideal. (Our stock big-bore test bikes usually run 1.72- to 1.85-second 60-foot times.) Since this was a baseline test of a standard Superbike engine and tranny, now the team can start experimenting with standard gearboxes and altered power deliveries. As Medley put it, “This was just a first stab. The second one will be deadly.”

Kosman Racing basically cut off the back of this ZX-7R, replaced the shock with a strut and added an adjustable 70-inch wheelie bar fully triangulated with the four-inch-over swingarm.
Kosman Racing basically cut off the back of this ZX-7R, replaced the shock with a strut and added an adjustable 70-inch wheelie bar fully triangulated with the four-inch-over swingarm.Photography by Lance Holst

Kosman's Chassis
A rare set of factory Superbike bodywork brought over from Japan for Tiger Showa's machine creates an initial impression of speed, and Muzzys worked with Kosman Engineering (415/861-4262) to make sure that impression was lasting. Prostar rules mandate stock wheels and DOT-legal tires, but Kosman completely rebuilt the ZX's rear end to trim weight. A single stock disc rides on the fork, which Lindemann Engineering lowered by four inches, dropping the bike into a menacingly evil stance. Interestingly enough, saving weight isn't that important because Pro Superbike will run with a minimum weight limit of 600 pounds, bike and rider combined.

Meyer and Medley made several chassis adjustments during our day of testing, playing with swingarm length and wheelie-bar angle and height, both men having considerable experience in dragracing chassis set-up. But the engine's inability to launch hard on the bar meant there wasn't much time to be gained with chassis adjustments. The bike went straight and steady, even with 12 pounds of air in the rear Dunlop D364, and Kosman's changes augmented the already ultra-rigid stock ZX-7R to produce a bike ready for more steam. Sport Rider has limited seat time on wheelie-bar–equipped bikes, so the day was a new and enjoyable experience for us as well. It's a safe bet that Medley and Meyer will take this machine to the limit, because every nut and bolt used on this initial experiment will be available in the '96 Muzzy catalog, proving that the company is serious about Pro Superbike dragracing.

Kosman Racing builds everything from Pro Stock dragracing chassis to adjustable triple clamps for roadracers.
Kosman Racing builds everything from Pro Stock dragracing chassis to adjustable triple clamps for roadracers.Photography by Lance Holst

A week later, this green meanie made a big splash at the Prostar finals in Gainesville, and hot-shoe Ricky Gadsen fired it down the quarter-mile in 9.48 seconds at 140.55 mph. Gary Medley won’t be happy until it runs in the eights, but that day isn’t far off, especially considering the mismatched gearbox and lack of an air-shifter, which the rules permit. The fans weren’t the only ones who liked this bike; the racers showed a great amount of interest because Muzzys ZX-7R represents an entry-level professional class based on the ultra-popular 750 Superbike class, and packs enough of a wallop to interest even jaded Pro Stock riders. It certainly got our attention.

For Sport Rider, a magazine that tests extensively at the dragstrip, this "E-Ticket Ride" answered some questions we've asked for many years. How quick would a Superbike dragracer be, and how much fun would it be to ride? The bike Gary Medley and Doug Meyer delivered to Gainesville answered those questions with enthusiasm and begins what we hope is a long run of Prostar's Pro Superbike. For straight-liners looking for a challenging bike to build and ride, Prostar's got a super class.

These Keihin smooth-bores started life as 39mm units, but Muzzys bored them to 41.5mm for roadracing applications. Fresh air from the front of the fairing is fed to a pressurized carbon-fiber airbox,
These Keihin smooth-bores started life as 39mm units, but Muzzys bored them to 41.5mm for roadracing applications. Fresh air from the front of the fairing is fed to a pressurized carbon-fiber airbox, though this feature is less significant to quarter-milers than it is to roadracers.Photography by Lance Holst
Temp Gauge
High Low
Bulletproof (we did 30-plus runs!) Prostar's minimum weight de-emphasizes technology
Great place for retired Superbikes Tall first gear sucks
Prostar's minimum weight helps assure parity We wanted to go eights! Rob...?

This article was originally published in the June 1996 issue of Sport Rider.