Kawasaki ZX-6R, Honda CBR600RR And Yamaha YZF-R6 - Maximum Middleweights
photographer: Brian J. Nelson
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.
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"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."
The standard switch cluster on the left clip-on remains but has new functions that work with the ECU and the dash display, such as limiting pit-lane speed or toggling between two saved fuel maps.
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."
Steve Rapp's beautifully prepared Attack Performance ZX-6R uses a mix of stock, Kawasaki kit and Attack Performance parts. Countless sensors record engine and chassis data as part of the bike's MoTeC engine-management system.
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."
 The latest Ohlins gas-charged TTX fork is mounted to Attack triple clamps. Marchesini 16.5-inch wheels are shod with Pirelli slicks, while Brembo monobloc calipers handle stopping duties. A CAN system communicates between the ECU and dash, with the sensors plugging into the rear of the dash as shown here. |  Formula Xtreme rules allow the stock swingarm to be braced and the axle tabs replaced. Attack welds on new tabs that incorporate the team's handmade quick-change equipment and allow the use of this tiny Brembo caliper. |  This small arm on the front axle is pushed out of the way when a socket is inserted; a tab behind the plastic guide is pulled away from a ratcheting mechanism that would otherwise prevent the axle from backing out, eliminating the need for safety wire and considerably speeding up wheel changes at Daytona. |
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."
Josh Hayes' Erion Racing Formula Xtreme Honda CBR600RR The engine modifications include Pankl connecting rods, Erion/CP pistons, an Erion-ported head with HRC cams and valve springs, an HRC close-ratio transmission and an STM slipper clutch. The exhaust pipe is an HGA (Honda's R&D department in Japan) stainless steel unit, and a huge Febur radiator keeps things cool. A MoTeC ECU oversees operations, connected via a custom-built wiring harness. Similar to the system used on the Attack Kawasaki, the setup offers control of practically every parameter related to fuel and ignition, including traction control. "We utilize all those things to try and tailor it to any particular track or rider preference," says Rick Hobbs, technical director for the team, but all that adjustability comes with a price: "There aren't many things I can think of that it doesn't allow you to do. It gives you so many things that it can be detrimental sometimes because you spend a lot of time focusing on things that maybe don't make that much difference to the big picture." The CBR's frame is stock, as is the swing-arm aside from the axle slots, which are enlarged to accept captive spacers. An Ohlins shock works the stock linkage out back, and up front an Ohlins fork is held by custom-made triple clamps. Interestingly, things like the triple clamps and rearsets are not adjustable; rather the parts are individually custom-made as needed. Wheels are 16.5-inch forged magnesium Marchesinis with Dunlop slicks fitted. "We've been running mainly 16.5-inch wheels," Matt Zurbuchen says, Hayes' mechanic for the Formula Xtreme bike. "Most of [Dunlop's] development is going into 16.5-inch wheels for modified classes. They have a pretty good idea when we show up to the track what's going to work for a front tire. There's always a choice between two or three tires for the rear that may work, and we'll have to figure out what's going to work." The CBR600RR was a new model for 2007, and while the Erion bikes were competitive right out of the box last year (aside from fuel problems that affected all the Hondas at Daytona) there was significant development time involved. "The bike in stock form is substantially better than the old bike," Hobbs reports, "but we had three years of development on the MEE [the part-number designation of the previous model] engine. So we had the new engine with a different cylinder head, cams, exhaust valves, springs, valve sizes and rod length, and it took us a little bit of time to get back to the level we were at with the older engine. Now we've exceeded where we were, but it took basically a season of development to figure out what we needed to do." Interestingly, Hobbs notes that the new bike is easier to work on than the previous model. General maintenance is much easier, and the rear shock can be removed and replaced quicker. And because the swingarm pivot doesn't run through the crankcase as it does on the old model, dropping the engine from the chassis is simplified. "It's very well engineered, and reliability is, I think, one of the strong suits-knock on wood." "[The chassis] seems to be a good baseline for whatever track we go to," Zurbuchen adds. "We're not making a mess of changes, front and rear wheel traction is always decent and we're not fighting chatter too much." While the team is understandably cagey with numbers, we were told that horsepower is more than 20 percent over stock, which works out to approximately 130 rear-wheel horsepower by our calculations-and we're sure that's a pretty conservative number, judging by the bike's performance on track. The CBR is within a few pounds of the minimum weight for the class, and with a titanium pipe replacing the stainless steel unit for 2008 Hobbs expects to be even closer to the minimum. "It was pretty easy [to reach the minimum weight]. Last year we had a stainless steel exhaust and no titanium to speak of. The wheels are about the trickest weight-saving part on the bike." "Hate to use this clich," Kento says after riding the Hayes CBR, "but it was a typical Honda with a well-sorted suspension and chassis, and it never wanted to do anything unruly, while giving you tons of feedback from the tires. The motor was much smoother than the Kawasaki but didn't quite have the screaming top end, with power starting to taper off just a bit past 15,500 rpm; nonetheless it's unbelievably quick for a 600 and felt like it would stomp a stock literbike." Bystanders could clearly hear the Honda's traction control kicking in when the bike was on the track, but Kunitsugu reports he could neither hear nor feel the engine missing and the Honda had smooth throttle response and came off the corners easier than the other bikes. Of the three bikes we sampled the Honda was set up the softest and the easiest to ride on Buttonwillow's bumpy surface. "I loved the chassis," Kunitsugu wrote in his notes. "It has the same nice feel as the stock Honda in the corners, especially during turn-in and while really pressing the chassis/suspension at the corner apex. It had a 'friendly' feel that didn't give me the impression that it could spit me off at any time, which obviously bolsters confidence. Suspension rates were probably the most suited to my speed and riding style and handled some of Buttonwillow's bigger bumps the best of the trio." Josh Herrin's Graves Motorsports Supersport Yamaha YZF-R6 Inside the engine, changes are limited by Supersport rules to cam timing, a YEC (Yamaha Engineering Corporation, the company's racing subsidiary) kit head gasket, valve job and higher compression ratio. Externally, however, Yamaha's kit ECU lets the team take advantage of the electronics incorporated into the R6's throttle bodies. In addition to the usual fuel- and ignition-mapping adjustments, the YEC black box allows the rpm at which the variable-length stacks operate to be changed. The addition of YCC-I, with this adjustability, is a big positive, according to team owner Chuck Graves. "You can have power down below and up top. Instead of always working to have it on one side or the other, now we can have long stacks and short stacks." Furthermore the ECU can alter the rate at which the electronically controlled butterflies open, and this can help the rider be smoother with throttle applications. A Power Commander piggybacked on the YEC box allows further fine-tuning of the fueling as well as the addition of a quickshifter. On the exhaust side the short Graves Motorsports 4-into-2-into-1 system is an off-the-shelf "works" header system, and the team is experimenting with the carbon-fiber canister's length. Other Graves parts include the rearsets, clip-ons, steering-damper mount and engine covers. Although data acquisition is not allowed in the AMA's Supersport class, the team tests with a Magneti Marelli system, which was installed for our test day. "We can monitor what's happening with the wheel speeds, the lambda sensor, suspension travel and what's happening with the rider and the brake pressure-all the things that we want to look at so we can help the rider and the mechanics refine the motorcycle," Graves says. We couldn't wrangle any overall power numbers out of the team, but we did find out the '08 model in Supersport spec makes 10 horsepower more in the midrange than last year's similarly modified machine and six horsepower more on top. The midrange improvement is in line with our findings on the stock bike, but the team has found some significant advantages in top end compared with last year's model. And though we found this year's R6 to be a few pounds heavier than last year's, the '08 racebike is slightly lighter-the additional weight on the stock bike is evidently all in the exhaust system. Suspension modifications are likewise limited in the class, and Herrin's R6 sports an Ohlins TTX shock along with Ohlins complete replacement cartridges inside the stock forks. Wheels are stock, shod with Dunlop DOT race tires. "There are usually three or four different compounds and constructions that will be available," Graves says. "Nothing really wild or out of the ordinary, which I think is good. I think on a race weekend if you had too many choices you'd just get yourself in trouble. You just need to pick the right compounds-what suits that rider-and the settings around [them]." Overall Graves reports that every change made to the '08 R6 is an improvement as far as performance in race trim. "We have better mass centralization; we have a better-balanced chassis, flexwise. The old bike was pretty stiff. This one has got a little bit better balance to it, and that's overall-from the fork tubes and the triple clamps to the frame and the swingarm. The engine makes more power; it has less friction and variable stacks. We got better valve springs this year and a higher-compression piston." Even after riding the Graves YZF-R6 back to back with the more powerful Formula Xtreme bikes, Kunitsugu raves about the Supersport Yamaha's power, handling and brakes. "Superb power from the engine, with way more midrange than a stock R6 could ever dream of. Transition to the top end was nice, not a harder hit like the Attack Kawasaki. Superstrong on top, obviously not quite as beefy as the two FX bikes, but unbelievably fast for a Supersport-spec 600. Power started to peter out above 15,250 rpm, so it was best to shift there. "The chassis was its real strong point, however-the same R6 agility it's always been noted for, only amplified on the racebike without being too twitchy or nervous like I was halfway expecting. Front-end feedback was excellent, and I always knew what the front tire was up to. Coupled with the razor-sharp steering I felt like I could put the Graves R6 anywhere I wanted in a turn, unlike the FX bikes that made me fight the big rear tire all the time. That's not to say the FX bikes were ponderous or anything; it's just that compared with the R6 they were a little heavier steering. Traction from the Dunlop NT D209s was excellent. The brakes were probably the best of the lot, even compared to the Brembos on the Attack Kawasaki, but that is really nitpicking. It's more that they were suited to my riding style, with a lot of progression, great feel and monster power." "He's a fighter," Graves says of Josh Herrin, the team's sole rider in 2007. "If we can give him a motorcycle that's pretty close to the window come race time, he'll make up the difference. Bringing Ben Bostrom into Supersport along with Josh, we have a benchmark to help Josh learn to set up a motorcycle and refine it for what his likes are and a benchmark for where the machine should be. We used Ben a couple of times last year to help us help Josh so that Josh would have a benchmark, and Ben's been super about that. This is exciting for us going into this year."
With numerous Formula Xtreme championships to its credit dating back to the mid-'90s when the class featured big-bore machinery, the Orange, California-based Erion Racing team knows a thing or two about building fast Hondas. In the hands of Aaron Gobert and '07 champion Josh Hayes, Erion CBR600RRs won all but a single Formula Xtreme race last year-an impressive record. Like the Attack Kawasaki, Erion combines HRC factory bits with the company's own products and select aftermarket parts for a potent end result.
The Erion team wouldn't let us take the seat off the CBR600RR for pictures, but there are plenty of trick bits to see with the fairing removed.
The stock dash has an Aimsports lap timer added, and the switchgear controls various ECU functions. The large numbered dial just fore of the triple clamp adjusts overall traction control.
Oversized axle slots allow the use of captive spacers to speed wheel changes at Daytona. Note the nonadjustable rearsets and trick CRG folding brake lever.
This ultra-trick CRG clutch lever folds up in the event of a crash, is adjustable for leverage and has a ball-bearing pivot. The red knob just behind adjusts the front brake lever.
With the early introduction of the '08 R6, Graves Motorsports was able to get a head start on developing the bike for AMA Supersport use, and by the time our test rolled around in early December Josh Herrin's '08 racebike was well into development. And according to the Van Nuys-based Graves team, the improvements from the '08 upgrades are just as noticeable in Supersport trim as they are on the stock bike.
The short canister helps move weight forward, as does the new magnesium subframe. An Ohlins TTX shock replaces the stock unit, and the stock rear disc has been Swiss-cheesed to save every ounce.
Everything but the tach and shift light has been covered on the stock dash, and an Aimsports lap timer is added. The clip-ons appear much longer than stock to give more steering leverage.
Without as much bling as found on the Formula Xtreme bikes, Josh Herrin's Supersport R6 makes do with stock wheels and brakes. Note the crossover tubes and tapered headers in the exhaust system.
All three bikes we rode were equipped with the latest Ohlins suspension; the Graves Yamaha R6 has Ohlins internals in the stock fork and this TTX shock absorber.
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