The Fat Boy is by far the most popular Harley-Davidson bike model and also a favourite as a basis for custom bikes, as many bike features on these pages show. The example shown here is further proof of a successful interpretation of a Fat Boy. What distinguishes it from others of its kind and makes it special can hardly be noticed by just looking at it, and only becomes obvious when opening up the gas. Screamin’ Eagle Stage 4 is the magic word, which gives it a huge punch.
Harley-Davidson has its own tuning department. Under the name of Screamin’ Eagle the most diverse performance components and kits are developed for the different stock bikes, with which the performance of the machines can be increased and optimized. The Stage IV kit used here is the maximum of the possible and was developed to gain maximum performance from the Milwaukee-Eight motors up to the red line.
The kit consists of Screamin’ Eagle cylinder heads with CNC-machined inlet and outlet channels as well as performance valve springs, Screamin’ Eagle throttle valve housings with 64 mm diameter, Screamin’ Eagle high flow injectors (5.5 g/s), Screamin’ Eagle bolt-on cylinders with 103.5 mm bore, 11:1 forged high compression pistons with aluminum coated piston shafts, high performance piston rings, SE8-515 camshaft, Screamin’ Eagle camshaft bearings, Screamin’ Eagle high performance tappets, multiple times coated cylinder head gaskets, top end, cylinder foot and camshaft lid gaskets, Screamin’ Eagle high performance clutch springs and discs.
After the power upgrade the Fat Bob now has proud 103 hp (instead of 55.69 hp stock) and a maximum torque of 145.23 Nm (instead of 114.51 stock). The power evaluation was carried out at the rear wheel and not on the gearbox!
In future the motor will breathe through a flow-optimized design air filter from Rick’s. For the exhaust an electronically adjustable system from KessTech was chosen. It is obvious that the stock engine cannot deal with the new components any longer. Rick’s Motorcycles has a modern Dynojet test bench on which almost any riding situation can be simulated and the mapping can be adjusted to the additional components.
Let’s now look at the custom parts that were used here. At the rear is a 300 wide tire on a design wheel from Rick’s. The 3-piece assembled wheel is available from Rik’s under the name “Supersteve”. In order to be able to use the wide tire, a swingarm from Rick’s was used with which the power is led via an intermediate shaft and a second belt past the tire to the pulley. The brake disc was located to the left side to enable a clear view of the design wheel. The design of the pulley, brake disc and wheel were matched to provide a harmonious look.
With the wider tire, a new wheel cover was necessary, and one of Rick’s own fenders was also used here. The same applies to the front fender, which now hugs the tire. A further highlight are the foot controls, also a Rick’s product, available in OEM position or forward by 2 or 4 inches.
Handlebar and grips are also from Rick’s, and the adjustable brake and clutch levers used here are absolute top sellers at Rick’s. Indicators are Kellermann products, with the “Atto DS” the smallest indicator with an ECE test mark, which can be used legally on the roads. At the rear is the 3 into 1 version with integrated brake and rear light. The front indicators were fixed below the instruments with Rick’s holders on the mirror screw.
Text & photos: Peter Schulz