Keeping your bike cool can be a tall order under some circumstances. Boyesen's Factory Racing Water Pump Kit might just make the difference you need. Boyesen took a look at the stock cover and impellers on most dirt bikes and improved them by increasing their pumping capacity and smoothing out the flow of coolant through the pump. First, Boyesen redesigned the impeller so that it moves more liquid by making the impeller blades almost twice as tall as those on the stocker. Each revolution of the impeller moves more liquid at any rpm. Since there's no thermostat to control coolant flow in a dirt bike engine, the water pump determines how the coolant moves through the engine and on to the radiators. At rock-crawling or slow woods speeds, low rpm can signal overheating. Having more coolant moving through the system faster can mean the difference between running hot and boiling over.Another problem with water pumps is cavitation, which occurs when naturally forming air bubbles in the coolant are met with turbulence inside the pump. In a water pump, cavitation can actually reduce pump output by half or more. To reduce this, Boyesen has redesigned the interior of the pump cover to accept a larger impeller and to eliminate any sharp edges and corners that can contribute to cavitation. If you look at the comparison photo of the Boyesen cover (top) and the stocker (bottom), you can see that the Boyesen cover has no sharp edges in the venturi.
With the Boyesen setup on the WR we immediately noticed a difference. The Factory Effex heat tapes we use on many of our bikes showed at least a 10-20-degree lowering of operating temperature and an ability to maintain it without wild fluctuations, especially at low speeds. We've subjected the WR to the MX track, technical woods single-track, hillclimbs, desert riding and everything in between. Since switching to the Boyesen unit more than six months ago, we haven't had to add coolant to our WR once and haven't seen any change in the coolant overflow tank level. With a list price of $109.50-$165.50 (depending on make, model and year), the Boyesen water pump kit is moderately expensive. Installation was easy, and the cover is available in black, magnesium or silver vein finishes.