Yoshimura Hayabusa X-1 - Heavy Bus

Turbo 'Busa
If you think northern Sweden is no place to base a motorcycle tuning firm, Erik Marklund of MC Xpress would disagree. "Because it's so cold and dark almost all the day in winter, we have plenty of time to work on the bikes," he says. "And in the summer it's light almost all the time and often hot. We have some nice straight roads with not many people or cars or police, so it's great for riding fast."

Erik has built a string of ultrapowerful specials since founding MC Xpress 10 years ago-turbo kits for sportbikes being the house special. He sold around 100 turbo kits all over the world last year. His latest and most outrageous project: the turbo Hayabusa.

The effort to cram the turbo into the very compact 'Busa was worthwhile. With its wastegate set at a not-too-radical 11.6 psi, the bike produces 328 hp at 9000 rpm at the crank-almost double the standard claimed max of 173 hp-and kicks out more than the stock Suzuki everywhere above 6000 rpm. Weighing little more than the standard bike, the big blown 'Busa has an almost identical power-to-weight ratio as Honda's NSR500 works GP bike.

The Mitsubishi turbo, used in some Volvo cars, is particularly suitable due to its built-in "pop-off" valve. "When a normal turbo is boosting and you close the throttle, the air has nowhere to go and produces a big pulse," Erik says. "This can destroy the hoses and intercooler and also means the turbo stops running, so if you open the throttle again you have no boost." Normally a separate valve is used to prevent this, but it's unnecessary with the Mitsubishi design.

Space was so tight in front of the engine Erik had to chop off the turbo's main air tube leading to the air box and reweld it to exit in a different direction. The standard Suzuki oil cooler and radiator are retained, but the rad is modified to make room for a large curved-aluminum intercooler (made by Erik) which cools intake air en route to the motor.

The standard fuel injectors are retained, but Erik adds a new bank of four Bosch injectors along with a new aluminum air box, a second fuel pump (the original is also used) and a fuel-pressure regulator. The original control unit for ignition and fuel-injection is unmodified.

The engine has to be stripped so that a 2mm aluminum spacer can be added to the bottom of the cylinder barrel, reducing compression to 8.5:1 from the standard 11.0:1. Stripping the motor is the hardest part of fitting the turbo kit, Erik says.

The kit costs $6000 through American Turbo Systems and includes an adjustable intake camshaft sprocket (to compensate for the spacer), bigger front final-drive sprocket, stiffer clutch springs and a stainless steel exhaust with carbon can. -Roland Brown

Importer:
American Turbo Systems
3435 Enterprise Ave. #50
Naples, FL 34104
Tel/fax (941) 403-0198
www.americanturbo.com

Yoshimura X1

By Hiroshi Sato

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