KRAFTWERKS is a Northern Californian company that has made its name developing supercharger kits for automotive and sport bike use. At the 2014 V-Twin Expo the company previewed its new supercharger kit, which it has developed for use on Harley-Davidson Big Twins.
During the Expo Kraftwerks described its HDBlower as being designed in such a way as to make it sympathetic to Harley-Davidson’s styling, and this includes using authentic H-D emblems on the casing.
Unlike other supercharger kits that make use of conventional positive displacement supercharger (i.e. roots or twin screw), Kraftwerks has not gone down this route as it believes such systems are inefficient compressors generating lots of heat, are very bulky, target power delivery at low end torque, which is already sufficient on a Harley, and are very noisy.
In order to countenance the perceived problems of a conventional blower, Kraftwerks decided to work with a centrifugal compressor. Rather than using an exhaust driven centrifugal compressor, such as a turbo charger, the company has adopted a centrifugal compressor, and have chosen the Danish made Rotrex.
The Rotrex supercharger employs a patented ‘traction’ drive system that is virtually silent and allows the supercharger to operate at internal rpms unmatched by other centrifugal superchargers and only rivaled by turbochargers, and has a compact drive section making it suitable for packaging into the limited space available on a motorcycle.
Kraftwerks claims that by using the Rotrex unit is has the best of both supercharging and turbo charging systems without any of the relevant penalties.
One issue the company had when it decided to use the Rotrex was the input shaft speed needed for it to run efficiently, which is significantly lower than that of an H-D engine’s rpm limit. To solve the under-spinning issue, Kraftwerks uses a two stage system to step up the input rpm. The first stage used is a ‘wet’ system; a silent chain drive that steps up the engine’s rpm by a fixed ratio of 2:1. The second stage is a cogged drive system where various drive pulleys and supercharger pulleys can be swapped out to achieve ratios as low as 0.731:1 and as high as 1.632:1. The wide rpm range capability allows the HDBlower the flexibility to utilize any of the C15 Rotrex chargers and to tailor how the power/boost comes in.
Kraftwerks’ first stage drive (transmission stage) is directly off the crankshaft. However, unlike other systems, it utilizes a bearing to support the drive gear and insures that radial forces caused by tension in the supercharger drivetrain are not transmitted into the nose of the crankshaft as bending or shear forces. Any forces that exist are isolated to the drive gear.
The kit has been designed as a two-piece unit for easy installation, and features a large flow-optimized plenum. Both the intake plenum and the belt cover are thermal insulated for heat shielding, and there is ram-air belt cooling for added reliability. An anti-surge blow-off valve is included for safety.
Kraftwerks states that the HDBlower kit can increase hp by 50 percent and torque by 25 percent.
Norco, California, USA
Tel: 951 808 9888