The Big Bore - Short Stroke Engine

Lots of modern motorcycles boast 'big bore, short stroke' engines, just what are the advantages of this kind of engine? The theory behind a big bore engine is simple – a bigger bore allows the use of larger valves and therefore you can get more fuel/air mixture into and out of the engine to make increased power.

But it doesn't stop there. The big limiting factor in an engine is piston speed. If the piston is traveling too fast reliability is compromised due to the internal stress. A big bore means a shorter stroke and a slower piston speed, allowing the engine to rev higher with improved reliability.
But there are downsides. It is tricky to get decent combustion on a big bore engine, as the air/fuel mixture doesn't have time to 'tumble' across the piston to achieve an even burn, leading to poor fueling. The only way to counteract this is to advance the ignition, a move that can also cause poor throttle feeling.

Clever electronics can overcome most fueling issues and the advantages of a big bore engine outweigh its disadvantages, which is why most performance engines are now big bore/short stroke engines.
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