Kawasaki ZX-6R, Honda CBR600RR And Yamaha YZF-R6 - Maximum Middleweights

While Ben Spies, Mat Mladin and Suzuki dominate the big-bore classes of the AMA's roadracing series, the Lockhart Phillips USA Formula Xtreme and Pro Honda Oils Supersport classes feature tighter grids and closer finishes among more manufacturers. In 2006 the FX title came down to a couple of points separating Eric Bostrom, Jason DiSalvo and eventual winner Josh Hayes. And in 2007 just a couple of seconds covered the top 20 Supersport qualifiers at any given event, with five riders winning races. At the end of the '07 season we arranged some time on the top bikes in each class: the Attack Performance Formula Xtreme Kawasaki ZX-6R on which Steve Rapp won last year's Daytona 200 and finished second in the FX championship; the Erion Racing Honda CBR600RR that Josh Hayes used to score seven wins on his way to the Formula Xtreme title; and Josh Herrin's Graves Motorsports Supersport Yamaha YZF-R6. While the Kawasaki and Honda are '07 models that return for combat duty this year mostly unchanged, the Graves Yamaha we rode is the new '08 version of the bike on which Herrin won the final Supersport round of 2007.

Steve Rapp's Attack Performance Formula Xtreme Kawasaki ZX-6R
Stripped of its bodywork the Attack Kawasaki is jewel-like in its finish and details. The data acquisition's extensive wiring and connectors are all tucked away or strapped down neatly, every surface is spotlessly clean and every individual part appears to have received attention in some form. This ZX-6R, ridden by Steve Rapp to victory in the '07 Daytona 200 and second place in last year's Formula Xtreme championship, was built in Richard Stanboli's Attack Performance shop in Santa Fe Springs, California, and is typical of the company's hot-rod approach to performance, with a mix of Kawasaki kit parts and Attack's own products.

"The engine is pretty basic," Stanboli says. "It has one of our cylinder heads on it; it has kit cams, kit bearings, a kit charging system and a lot of little stuff that we do. A lot of it is labor-intensive; there aren't really a whole lot of parts. The bike's been so reliable and so strong that we haven't had the need to change rods or valves. This year we'll probably do a little more development, but for '07 it was a pretty basic package." While the transmission internals can be changed according to FX rules, the Kawasaki's stock ratios are better suited to most of the AMA tracks than the kit parts are. Likewise the stock slipper clutch is employed with some tweaks. "We change the amount of spider springs to tune the slipper clutch, and we change the amount of spring force on the plates to give it more slip. You can get carried away with the amount of slip you have, but there's enough drag in [the clutch] right now; we've kind of inched our way to where the guys want it."

Coordinating and recording the engine's activities is a MoTeC ECU, which Stanboli prefers because it gives him complete access to the base fuel and ignition maps rather than having to trim the stock or kit ECU base maps. In addition the top and bottom injectors can be individually controlled, timing can be adjusted for each gear, ignition and injection can be trimmed for each individual cylinder, and traction control, launch control and wheelie control can all be incorporated. Attack had tested previously with a similar system on its Superbike and Superstock equipment and found advantages to using the traction control, but Stanboli says, "The 600 didn't seem to want it as much. If you have good grip why give away horsepower? You can make it easier for the guy to ride it when the tire gets slippery, but I think it catches some people out."

The Kawasaki's chassis is equipped with Ohlins' latest TTX suspension and liberally peppered with parts from the Attack catalog, including the rearsets, clip-ons, adjustable triple clamps and bodywork. Stanboli reports that the 350-pound minimum weight requirement was easy to meet with the ZX-6R, even using steel rather than titanium fasteners and fiberglass rather than carbon-fiber bodywork. The frame and rear suspension linkage are stock, as is the swingarm, except for custom axle blocks welded on to accept Attack's handmade (and very trick) quick-change setup. The MoTeC ECU also looks after data acquisition, and in addition to all the engine parameters the system records front- and rear-wheel speeds, brake pressure, suspension stroke, rear-tire temperature and tire pressures both front and rear via tiny radio transmitters incorporated into the valve stems.

Stanboli will only say that horsepower is "the same as the Erion bikes," but cites linear power as the ZX-6R's strong point. That and "a solid chassis in that you can ride it hard and it's pretty well balanced. [The riders] can hop on it and go fast right away, so we haven't had to change the balance of the steering effort on the motorcycle that much; even the offset in the clamps stayed relatively [in the] stock position. We play with the damping and you get the forces right in the springs, and that's basically it."

Compared with the Erion Formula Xtreme bike and Graves Supersport bike, Editor Kent Kunitsugu reports that "the Attack Kawasaki was a rip-snorting, unruly beast that required being grabbed by the neck and wrestled into submission. It had the strongest engine of the trio, with a serious midrange punch that sailed into a monster top end and continued making major power all the way to the 16,000-rpm limiter. While I wouldn't say it was head and shoulders above the Honda on top end, it was definitely noticeably faster."

Kento also writes that throttle response on the Kawasaki was extremely smooth, and as with all three bikes fueling was crisp. While the chassis was set up ultra-stiff for new recruit Chaz Davies at Daytona, the Attack bike steered well once some softer fork springs were installed. Feedback from the Pirelli 16.5-inch slicks was good, according to our man, and "seemed to be very similar to the Dunlops on the Honda, although the Pirellis were more stable under braking. At maximum lean the Pirellis seemed to feel softer on the sidewall than the Dunlops. Brakes on the Attack Kawasaki were awesome in power and had much better feel than the Brembos on the Honda."

"We went to Daytona and we won," Stanboli concludes. "We were competitive right out of the box, which kind of surprised us a little bit. We had thought we'd inch into it through the year because it's a brand-new bike."