From the Manufacturer
Tested and developed under the most extreme racing conditions to suit the requirements of professional drivers and weekend club racers alike, the Viper VST 4.5XL and 5.5XL 550 class brushless motors are the perfect choice for your 4x4 short course racing machine. Viper VST XL motors are ROAR approved for the 2011 season. Based off the proven Viper VST 540 platform, the XL motors offer the most recent in Viper engineering and design. The 72mm long can contains a butter smooth two pole power band, fully sensored design with integrated internal temperature sensor, and top grade ball bearings for long life and low maintenance. The VST-XL series will provide you with the precision and control required on slippery surfaces, and the raw power necessary to win under high traction race conditions. The XL series are perfectly matched to the Viper VTX10R speed control and will surely be an unbeatable combo.