Fred Bertrand’s supercharged Yamaha SR400 single is engineering perfection
Supercharged Yam special
Fred Bertrand’s Krugger Motorcycles are a Belgian-based custom shop with a glittering array of world class awardwinning builds. Inspired by the pinnacle of Motogp racing, Fred has given this little Yamaha SR400 engine (97mm bore x 62.7mm stroke for 399cc) some serious work. The most noticeable difference is the beautiful Aisin 300 supercharger with its custom-built plenum chamber.
Fred said: “It was easy enough to fit the supercharger into the space on the SR but the challenge was to machine everything to be able to run the belt drive for the supercharger with the original rotor/mag. The engine runs a slightly lower compression of 8:1 (compared to the stock 8.5:1) and I had to build a plenum chamber that’s 250% of the original engine capacity (one litre). The supercharger works at three times the speed of the engine crankshaft and delivers 700 grammes of boost (9.95psi).
“I did the initial calculations to set the system up and then it was a question of fine-tuning. It makes a reliable 45bhp (compared to the stock 27bhp @7000rpm). The engine never stops accelerating. It’s really nice to ride.”
The beautifully polished fork legs, sitting in equally well polished stock yokes, have been lowered and work with a set of Fox shocks at the rear. Wire wheels are shod with a set of Dunlop K81s, inspired by the first tyre to lap the Isle of Man TT course at over 100mph.
Fred’s obsession with perfection spills across the SR400 with so many neat touches. Motogadget speedo, switches and grips sit behind a tiny custom cowl at the front above a modified top triple clamp and custom handlebars. The single disc front brake and clutch have been given an upgrade and are by Beringer, adding some power over stock to match the supercharged 400 motor.
The standard SR400 fuel tank has been kept, but reworked narrower and longer with the filler cap relocated centrally. It now resembles the style of an OW31 TZ750 petrol tank, while a custom tail unit hides all the electrical components.
“This Yard Built really is a unique piece of art,” commented Yamaha Motor Europe Marketing Coordinator Cristian Barelli. “I think it’s impossible to have a custom machine that lives and breathes our racing history better than this.
“It’s such a beautiful bike and the longer and closer you look at it the more detail you find to enjoy. You wouldn’t normally associate the SR400 with Motogp racing but this build is as genuine and authentic as it’s possible to get, a real Yard Built special!”
Krugger’s supercharging has almost doubled the SR’S power
Tiny cowl, Motogadget dash and polished yoke
Engine cases are beautifully finished
The exhaust note is pretty damn fine
Single-seat conversion is perfection