Bimota YB4 EI

 

 

 

Make Model

Bimota YB4 EI

Year

1988
Production 303 units

Engine

Four stroke, transverse four cylinder, DOHC, 5 valves per cylinder.

Capacity

749 cc / 45.7 cub. in.
Bore x Stroke 68 x 51.6 mm
Compression Ratio 11.2:1
Cooling System Liquid cooled

Induction

Weber Marelli electronic fuel injection

Ignition

CDI
Starting  Electric

Max Power

121 hp 89 KW @ 10500rpm

Max Power Rear Tyre

72.7 kW / 97.5 hp @ 10400 rpm

Max Torque

88.3 Nm / 9.0kgf-m / 65.1 lb/ft.@ 8500rpm

Transmission

6 Speed

Final Drive

Chain
Frame Two diagonal beams in section bar made of aluminium with internal ribbing. The cylinders are supported by plates bolted to the beams and the swing arm is made of aluminium

Front Suspension

42mm Gas telescopic forks, external adjustment for anti-dive

Rear Suspension

Gas single shock, external adjustment

Front Brakes

2x 320mm discs

Rear Brakes

Single 230mm disc

Front Tyre

3.50-17

Rear Tyre

5.50-17

Dry Weight

180 kg / 396.8 lbs.

Fuel Capacity

20 Litres / 5.3 gal

Consumption  average

6.5 l/100km / 36.2 mpg

Braking 60 - 0 / 100 - 0

13.2 m / 36.0 m   43.3 ft / 118.1 ft.

Standing ¼ Mile  

10.8 sec / 201.8 km/h / 125.4 mph

In race trim, this motorcycle won the 1987 Formula-One World Championship and ended five years of Honda domination in the most important four-stroke racing class. It was a victory that marked the arrival of Bimota on the world stage. The tiny Italian factory had taken on the mighty Japanese works teams and beaten them fair and square.  Originally the YB4 was a pure racer unavailable for road use. With the advent of the World Superbike Championship in 1988 and its strict homologation rules, Bimota were obliged to build 200 YB4s in order to compete. Inevitably some ended up on the street. They also took the opportunity to make one important change - their Formula-One racer had been normally carburated, but the YB4 that finally went into series production was fuel-injected.  The YB4 has always used a Yamaha FZ750 engine, the pioneering five valve, steeply inclined unit launched in 1985. The standard FZ engine never lacked top end power but was weak in midrange and low down output. It takes some winding up. Bimota's aim was to boost performance through fuel injection. The Weber Marelli electronic system in concert with the ignition advance liming meters the optimum amount of fuel and air through an injector into the intake manifold, to produce the ideal charge at a given rpm.

There are sensors to measure the throttle opening, phase of the engine, coolant and air temperature, and air pressure is regulated at a constant three bars. Ignition modules adjust the coil charge, and the whole system is managed by a black box which has an interchangeable chip. In theory, unburned gases are minimized and fuel consumption reduced. As the engine is being fed the ideal mixture, power is increased across the rev range.  Although very fast in a straight line, it is not power that gives the Bimota its main advantage, rather it is power-to-weight and a beautifully crafted chassis keeps that weight low. The YB4's dry weight is a keen 180kg.

The engine is used as a stressed member held in place by massive aluminium beams with huge castings supporting the critical areas around the steering head and rear swingarm pivot. Bimota pioneered aluminium perimeter frame development at a time when all the other manufacturers were still using steel double cradles and their original ideas on how to house heavy Japanese engines have been shamelessly copied. Today, perimeter frames are commonplace. 

 The YB4 has totally neutral handling - its behaviour is predictable, smooth and supremely forgiving. The steering is sharp and responsive, the suspension stiff and expertly damped. Its quick steering and short wheelbase allow it to change direction very rapidly, yet its handling is never nervous, it feels solid, low and compact, always letting the rider know exactly what the tyres are doing.  Such was Bimota's success with this bike during its heyday of 1987-1989, Yamaha were forced to release their own World Superbike contender, the OWOl, featuring a comprehensively revised FZR750 engine, larger bored, shorter stroking and making appreciably more power than the five-year-old FZ750 design.

Because of the homologation rules though, Bimota would have to build another 200 bikes in order to use the new engine. Fuel injecting the older engine has helped increase the power but really it is Bimota's wonderful rolling chassis that keeps the YB4 on the pace and in the hunt. It is a complete, perfectly balanced motorcycle. Racers say that riding it almost becomes an extension of the will, so direct is the feeling of contact with the track surface. All you need is the will to win, and this gorgeous looking motorcycle does the rest.