By definition an ATV is an All Terrain Vehicle, able to handle a number of different duties or environments without complaint. However when a very specialized use, like motocross is the intended venue, some compromises to the overall All Terrain's are in order.
Take Holz Racing Products (HRP) KFX400 as a prime example. This specialized machine has custom fabricated parts dripping from it. The Washington-based shop tore this KFX400 down to its frame, and then revamped the suspension and chassis components to lower the ride height 2-3 inches while increasing front wheel travel to 11.5 inches and rear wheel travel to 11 inches. This was achieved using HRP's long travel front suspension kit with Custom Axis boingers up front and Holz's round housing swing arm, Custom Axis shock, and Axcaliber rear axle out back.
HRP further improved the handling with some smart changes to the controls. By creating a chromoly steering stem that's 1.5 inches taller than stock, the shop greatly increased its options for handlebars, since the quad could fit motorcycle bars as well as ATV units in its new configuration for optimal race ergonomics at the hand grip. Renthal Fatbars with 50/50 grips and a Suzuki DRZ 400 twist throttle were added for better handling, and precise steering.
Improved stopping power would also be a great help on the track and to that end Braking pads were tossed into the mix on this MX machine. Holz also made stainless steel brake lines for better feel, and more pressure to the master cylinder. They followed up by drilling the rear rotor to reduce unsprung weight, improve heat dissipation while braking.
HRP also armored the KFX400 MX to protect the motor, chassis, oil tank, and lines during its rigorous motocross career. The shop's full chassis skid plate, front bumper and skid plate, and rear fender mounts fill that bill quite nicely; the plates were CNC-fabricated from 1/8-inch thick aluminum while the bumper is TIG-welded chromoly.
Brian Billings Racing Products put together the power package for the motor using DRZ 400 cams and valve springs to better utilize the added fuel from the Keihin 41mm FCR carb that replaced the smaller stock piece. Compression was bumped up to 13:1 courtesy of some J&E pistons. However, the crowning touch here was a DRZ 400 ignition-its higher rev limit lets the KFX take full advantage of the increased power.
We had a chance to ride Holz's creation at Glen Helen's Vet track and found it the picture of the race-ready Z, although a bit down on power compared to most track weapons we've sampled, as the 110 degree heat caused the Washington-tuned motor to run on the lean side.
For now this maker of snowmobile racing parts is concentrating on a line of products for the LT-Z400 (and its ilk) although proprietor Mark Holz envisions expansions into new quads from Yamaha and Honda, as well as popular older offerings like the 400 EX.