Bimota’s Ground Breaking, Two-Stroke Rocket
This bike will have sport riders’ pulse rates racing into overload — before they even get into the saddle.
Early next year a milestone will be written into the history books when series production starts on the first two-stroke motorcycle in more than 10 years to meet the EPA requirements of all 50 states in the USA, and anywhere else in the world for that matter. And what a motorcycle it will be. Bimota, the constructors of the most exclusive sport bikes in the world, will unleash their 500cc two-stroke V-twin, dressed to kill in full race-tech livery.
This bike will have sport riders’ pulse rates racing into overload — before they even get into the saddle. The Due will obviously be competing for the title of Ultimate Sports Machine.
Bimota has spent over six years developing this wonderful piece of machinery, not surprising since the RD department has never had more than single figure staffing levels. Traditionally Bimota has borrowed powerplants from their Far Eastern industrial colleagues and wrapped them in exquisitely crafted frames and bodywork. Recent Bimota models have seen increasing applications of fuel injection to the engines, and this has served as the proving ground for the development of the Direct Injected two-stroke engine.
With their roots in racing, Bimota initially hoped to develop the engine for use in GPs, encouraged by the debate within the sport early in the decade about banning 4-cylinder configurations. Fortunately for all of us, the level of investment to develop a complete new bike for GP racing forced a change of direction that resulted in the imminent arrival of the street machine.
The Due will obviously be competing for the title of Ultimate Sports Machine.
Interest in two-stroke power plants has been widespread within the motorcycle and auto industry for the last 10 years, sparked by the development of a new breed of fuel injectors by the Australian company Orbital. The new system provided a granularity of fuel atomization that made their application in a two-stroke engine a practicality.
Two-strokes are of interest to the automotive industry due to their simplicity and high power-to-weight ratio – if only they weren’t so dirty and fuel inefficient. Both these phenomena are caused by the two-stroke principle of using fresh, fuel-rich intake air to clean or scavenge the cylinder of exhaust gases. The tuned exhaust systems try and prevent much of this charge from escaping out of the cylinder with the exhaust gases, but a lot still does.
With direct injected fuel, this is no longer a problem as air can be used to expel the exhaust gas, and the injectors only fire at the moment the exhaust ports have closed. Result is nice clean exhausts, free of unburned hydrocarbons, and un-polluted clean fresh charge waiting for the big bang of the next ignition pulse. Two-stroke heaven. Bimota has a simple slogan they claim is at the heart of all their RD work — Tecnologia dell’Emozione .
Too good to be true, right? Well, just a little. Honda tried some fuel injection on their NSR500 GP machine during 1993, but it was dropped after that season.
Surprisingly they chose to inject into the crankcase in a straight emulation of the operation of a carburetor, and as a result found similar performance to a carburetor. This could have been forced on them by the very short time that is available for fuel atomization in an engine turning at 13,000 rpm. Uneven or incomplete atomization would result in uneven or incomplete ignition and lower top power output.
The Bimota Due has quoted maximum power develop at 9000 rpm and the difference in engine speed may be just enough to eliminate this problem. Interestingly, the new Honda NSR500 V-twin racer delivers its maximum power of 135 bhp at 10,250 rpm, pumping AVgas through conventional carburetors.
Talking to the Bimota staff at the recent IFMA show in Cologne, they made it clear they wanted to start production as soon as possible, and were hoping for an initial production run of 500 units.
The exact configuration of the fuel injection system is not yet known for the Bimota, but it seems that they have chosen to scavenge the exhaust gases by pumping fresh air through the crankcase and the conventional two-stroke transfer ports. Reed valves are still used to regulate the flow of air into the cylinder, each cylinder being supplied through a separate reed block. There are six transfer ports and three exhaust ports, a common configuration for contemporary two-strokes.
The fuel injection system will be linked into an engine management system that checks many of the factors that influence the amount of fuel to be injected, including air temperature, water temperature, exhaust gas temperature and airbox pressure.
Another major contribution to the clean exhaust of the Due is the use of the gearbox oil to lubricate the main bearings, rather than relying on the fuel/oil mist of regular two-strokes. Cylinder and crankshaft lubrication is still performed by two-stroke oil, flowing down small galleries into the guts of the engine. There is a two liter oil tank partition to the fuel tank that will need very infrequent topping up.
The racing heritage of the machine is obvious, with a hydraulically-actuated dry clutch and 6-speed side-loading cassette gearbox that will come in handy if you want change your gearing for your favorite set of curves. The frame follows Bimota’s recent preference for oval profile alloy pipes, with an Ohlins rear shock and 46mm Paioli fully adjustable front forks. Carbon cans keep the exhaust note muted and carbon fiber is also used for the seat.
Brembo discs, Antera alloy wheels and Michelin Hi-Sport radial tires complete the list of top range equipment.
Talking to the Bimota staff at the recent IFMA show in Cologne, they made it clear they wanted to start production as soon as possible, and were hoping for an initial production run of 500 units. This may not seem like a lot, but when you consider that last year Bimota produced less than 1500 bikes, it represents a massive part of their operation.
Further questioning revealed that the bike was quite literally not ready for the show until the last minute, and some inconsistencies between spec sheets suggest that it may not yet be ready for full production. On the other hand, now that the project has got as far as it has, Bimota will want to start production as soon as possible to start recouping the enormous investment they have made in the new engine technology.
Bimota has a simple slogan they claim is at the heart of all their RD work — Tecnologia dell’Emozione . In the 20 years since their first Kawasaki powered KB1 production bike, Bimota’s motorcycles have played havoc with the emotions of the world’s sport bike community. The 500cc Due proudly carries this tradition through to the closing years of the decade.
Result is nice clean exhausts, free of unburned hydrocarbons, and un-polluted clean fresh charge waiting for the big bang of the next ignition pulse. Two-stroke heaven.
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