Yosh racer in latest Superbike (UK) issue

[OB_Animal]

Nice article and more details about mods Yosh Japan did to their racing Busa.
Also short review by Terry Rymer of the ride he had on their 2nd bike in one of the races for the Jap unlimited race-class.
BTW, surprising to see how much of the engine is still stock and it's also pleasantly surprising to hear about longevity even in this hopped-up trim!

 

[OB_gsx1300rguy]

Hey what mods are done to that bike?

 

[OB_Animal]

Here we go:

Engine/power related:
Counter-balance shaft removed and lot of time spent on lightening and balancing crank.
Stock rods, Yosh Japan race cams and high-comp (12.8) pistons, stock valves and springs inspite of 11,300rpm rev-ceiling. Heads ported/polished, extra pre-load spacers on the clutch, close-ratio gearbox. They use Motec (Australian, car based) computer for EFI/ignition and still use the OEM/stock single injectors. Flapper valve removed from airbox. Side-stand cut-out switch used for quick-shifter triggering. Cooling was a problem, they now use 2 radiators above eachother and adapted from car-use keeping it cheap, oil-cooler mounted behind top radiator and also a Yam R1 watercooled oilcooler is used. Titanium exhaust with Tri-Oval end-can. Outside/underside part of OEM clutch-cover has section cut out and flat plate welded on again for ground clearance. Race class rules there dictate use of simple unleaded pump gas.
They won their class at the Suzuka 8 hours (you know, the one race per year where some of the worlds best GP500 and WSB cracks fight it out with Japans top home boys) and when they pulled the motor down afterwards in this 203HP@11,000rpm form it still looked ready for another 8 hours.

Chassis/handling related:
Rear swingarm is from GSX-R750 Superbike kit, went right in and was shorter. Ohlins shock, different top-mount (new lug welded to frame) and new bottom-bracket and linkages as well. Front forks are Ohlins from GSX-R750 as well and Marchesini wheels too (stock front size but rear's a 16.5/6). Steering stem moved back an inch and tilted differently for stock rake and increased trail. Swingarm pivot point lowered in the frame 5mm and Yosh' own top yoke. Nissin 6 pot front brake calipers.

Tires are still a problem (there's nothing out there for a bike like this), riding it is definitely a challenge, topspeed at the end of Suzuka's straight at 179 mph is 2 mph better than GP500 bikes on same day and their #1 rider qualified just behind Haga and his WSB-spec R7.

Terry (too tall) Rymer from the UK rode it as #2 rider in the last race for the All-Japan championship at Motegi circuit (Honda's new home track - 2 ring Motegi) in the Formula X class (similar to US Formula Extreme I think) and came away impressed. He thought that it could possibly win a WSB round at a high speed track like Germany's Hockenheim because of the unbelievable speed in the upper gears. Terry is normally riding Endurance racing classes (think he's a multiple world champ there) on tackle that's just a bit below WSB machinery and was quoted "... but once it gets into 4th and 5th it's a bloody missile, just keeps pulling and pulling".

Think that's enough for now.

 

[OB_DangerMouse]

Another interesting thing is Yoshi claim a further 20-30BHP would be easy to achieve, Terry said that trying to put all that horsepower down is already a problem but okey'd the development of the more horsey motor anyway!

I reckon a more powerful less torquey engine would get the power down more easily out of the turns as you could short shift and use more throttle by using the engine 'off cam' to reduce wheelspin.

I reckon it also proves a lie to GPs horsepower claims which I've always felt are exaggerated, Mags tend to add about 5 BHP to the claimed power outputs every season just because they assume it will be more, in reality there haven't been any breakthroughs with two strokes for over a decade and I doubt if they are any more powerful than they were then, if the Yoshi Busa was 2 MPH quicker than the much lighter GP bike which would have had at least a 10 MPH higher corner speed onto the straight, then that suggests that the GP bike is at least 20 BHP down on the 200BHP Busa - making up for less corner speed and still being quicker at the end of the straight is no mean feat.