Blown SR400

Fred Ber­trand’s su­per­charged Yamaha SR400 sin­gle is en­gi­neer­ing per­fec­tion

Motorcycle News (UK) - - This Week - By Gary Pinchin MCN CON­TRIB­U­TOR

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

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