Modified Middleweight Comparison: Kyle Racing's Honda CBR600F4—From The Archives

This article was originally published in the April 2001 issue of Sport Rider.

You wouldn’t be blamed for mistaking the Kyle CBR for a full-blown racebike. The headlight and taillight are so subtle—but look closely, they’re in place. In fact, rather than being a modified streetbike, Dan Kyle’s bike is a racebike, ridden in the AFM Formula 40 class by Tony Jimenez and modified for street use.

The Kyle bike’s chassis is virtually identical to the bikes raced by the team in the PACE/Formula USA Sportbike class (with rider Owen Weichel winning the fall Daytona round) and features some trick bits allowed by the PACE rules, which you wouldn’t see in say, AMA Supersport. The setup incorporates a tall chassis with a steep swingarm angle and lots of trail, which Kyle prefers because it gives better front-end feedback. To this end, the stock fork has been lengthened, and the internals polished and modified to Kyle’s specifications. Interestingly, Kyle runs a mix of fork springs, with a progressive-rate spring in one side, and a straight-rate in the other. The tubes are gripped by Attack Performance adjustable triple clamps, set at 6.5mm less offset than stock.

Stock brake disks (with stock calipers, HRC pads and Galfer lines) mount to stock wheels powdercoated by Maas Brothers—more than one person didn’t believe those were the stock hoops—which wear Dunlop D207GP Stars. Out back, a Fox Shock bolts to a less progressive linkage “made using parts from another Honda model,” according to Kyle. Ergonomically, Moriwaki rearsets allow footpeg position to be adjusted, and CBR1100XX clip-ons mounted below the top triple clamp allow for further fork-height adjustment. The Kyle Engineering Honda tipped the scales at just 365 pounds with all fluids but gas, more than 40 pounds less than a stocker. Shrouded in its Sharkskinz bodywork, the F4 appears to be more of a racebike than a streetbike. The barest concessions for street use are a small automotive light hidden behind the windscreen and an LED brake/taillight tucked under the seat cowling.

While the chassis may meet F-USA rules, there’s no way the F4’s engine puts out less than the Sportbike class mandated 106 horsepower. The CBR’s engine utilizes a mixture of Kyle-massaged parts and HRC goodies to produce a maximum of 119 ponies, along with some impressive power levels lower in the rpm range. Kyle begins with a stock crank and balanced stock rods, and uses 3mm-over JE pistons (manufactured to his own specifications) to attain 654cc of displacement. Stock valves with HRC springs and APE titanium retainers are worked by degreed HRC kit camshafts. Kyle has the retainers hardened with a nitride process creating a surface layer of titanium nitride, similar to the gold coating commonly seen on fork tubes. (This keeps wear in the valvetrain to a minimum.)

The cylinder head has been shaved to bump up compression, along with having its ports cleaned and matched. Giving further indications of the bike’s racetrack intent, a HRC close-ratio transmission is fitted, and a lightened, stock flywheel precludes the use of a charging system. Luckily, we didn’t plan on straying far from the battery charger. Other HRC accessories include a quick-turn throttle, tachometer and a selection of ignition boxes with different rev limits. Surprisingly, the carburetors, airbox, air filter and clutch are all stock—although Kyle sometimes uses Barnett plates.

After some chassis tweaking to better suit the tall chassis for the dragstrip, the bike carded a 10.337-second at 136.050 mph quarter-mile run. Segueing to HPCC for top-speed testing, Kyle juggled rev limits and gearing for a commendable 176 mph—exactly 20 mph more than a stock CBR600.

But it was the road course where the CBR felt at home, and while the bike was set up more for the shorter tracks where it normally competes, the stable chassis and torquey motor helped the Kyle bike to card a 1:27.2 lap time.