Outdoor Motocross Bikes Up Close - Dirt Rider Magazine

Sound
01 Pro Racing sound regulations have been the same since the start of the SX season, but as teams work with exhaust companies to chase former power levels while still meeting current sound restrictions. The Muscle Milk KTM team was running these pre-canisters on the mufflers. The bikes were very quiet, but obviously made a lot of power.02 Pro Circuit was in on the innovation as well. This bulge in the header looks like the FMF Powerbomb, but FMF has that patented, so we suspect that this is a pre-muffler something like a two-stroke silencer. The idea is not new. KTM open-class two-strokes came stock with just such a system in the mid-'90s. Note that the tight bend of the titanium header is double-walled for strength.03 The Pro Circuit teams weren't alone in attempting to protect exhaust systems. The works Honda Yoshimura systems sported this sexy carbon guard. Hot titanium is relatively fragile, so protection is a good idea.Heat
04 When the races head outdoors, the teams really start several new battles they avoid in SX. One is heat. The longer motos, deep dirt, steep hills and brutal ambient temps play havoc with modern four-strokes. Here KTM has shrouded the carb with carbon and heat tiles to keep the mixture temps down.05 Many of the top 250F teams run oil coolers to keep the oil temperature down. The little bikes abuse the clutch, and the heat put into the clutch goes directly into the oil, and that is tough on the engine.06 Kawasaki has won a huge number of 450 outdoor races in a row, and perhaps it is not a coincidence that the factory KX450F runs a Boyesen water pump system and an oil cooler. Then there is heat insulation on the cooler lines to prevent adding exhaust heat to the oil by accident.07 Virtually all of the teams insulate the bottom of the fuel tank in an effort to keep the fuel from heating and even boiling. This would happen with pump fuel, but the problem is even worse with the unleaded fuel that is required by AMA standards. Nope. Pump unleaded won't pass.Mr. Clean08 Racing is about selling bikes, so the teams all take extraordinary measures make the bikes clean enough for a museum and trick enough for the space shuttle. The problem outdoors is keeping the bike looking like Davi Millsaps' Honda does here.09 How long into the first moto do you suppose Ryan Villopoto's KX450F looked like this? The roost from riders at this level is like the sandblasters used on freeway graffiti.10 It is one thing to know that the scoring is now managed via transponder, but did you ever stop to consider the number of transponder units we are talking about and the care required to manage those? This table full was still left well into the tech inspection cycle.