High Revving VS Low Revving Engines: Advantages And
Disadvantages
As two-wheeler enthusiasts, we sometimes come across as a divided bunch. Some of us love high revving supersport motorcycles because of the performance and thrill they provide. Riding a motorcycle with an engine that spins north of 10,000 rpm is a feeling that few other things could match. On the other hand, there are enthusiasts who love cruiser motorcycles which are more relaxed and suitable for easy-paced highway mile munching. Both the classes of motorcycles have their fan bases not only because of their respective bodily characteristics, but also because of the nature of their engines. Generally speaking, supersport motorcycles feature a high-revving engine and offer very quick acceleration and top speed, whereas cruiser motorcycles with their low revving engines are torquier, relaxed and effortless. So what makes these engines high or low revving, and what are the respective advantages and disadvantages of the two engine types? Let’s find out.
Bore vs stroke
Everything we discuss in this article will primarily depend on two crucial parameters of an engine’s cylinder, namely bore and stroke. Simply put, bore is the width of an engine’s cylinder opening where the piston slots in. An engine’s stroke, on the other hand, is the height of the cylinder where the piston travels from the lowest position to its highest position. It’s the dimensions of the bore and stroke that define the rev friendliness of the engine.
High revving engines
A high revving engine, also sometimes known as a short stroke engine is an engine where the bore is bigger than the stroke. The engine componentry on such engines is deliberately kept light to facilitate more revolutions per minute. The shorter the stroke, the lesser the distance covered by the piston, and the easier it is for the piston to go up and down its operating range more times every minute. This is what we also term as revolutions per minute, or rpm, which defines the revviness of an engine. A bigger bore also allows for more space for valves, which helps intake and exhaust systems to function more effectively. An engine designed to rev higher is generally meant to produce a high amount of horsepower for any given cubic capacity. These engines are usually found in high performance sports bikes, like the TVS Apache RR 310.
Advantages of a high revving engine
• Due to lesser space for movement, short stroke engines have lesser inertial stress which allows them to be equipped with faster valve timing. The result will be more combustion cycles per unit of time, leading to more power being generated for any given cubic capacity
● There is more space for intake and exhaust valves to be fitted in, thanks to the bigger bore. With space for larger or more valves, the intake and exhaust systems work more efficiently, allowing the engine to produce more power while retaining compact dimensions
● If horsepower numbers are what you are looking at, high-revving, short stroke engines are a better option due to their higher specific output, or power produced per unit of cubic capacity
● Due to their advantage in terms of performance, high revving engines are preferred over low revving engines for high performance track racing, and are generally considered the benchmark for high-performance motorcycling.
Disadvantages of high revving engines
• High revving, short stroke engines often have a relatively weak bottom end. They don’t have much torque lower down the rev range
● With most of the power and torque sitting higher up the rev range, these engines have lesser tractability. One needs to keep the engine in its power band to extract the most out of it
● High revving engines are not effortless when it comes to cruising. The engine would spin at a higher rpm at cruising speeds when compared to a long stroke engine
● High revving engines are relatively less fuel efficient due to more revolutions and combustion cycles per unit of time
● While short stroke engines are quite powerful, they don’t generally boast a very high torque output. So while they accelerate quickly and reach very high speeds, they are not suitable for load lugging, and don’t make for very good touring engines
Low revving engines
Low revving engines have a smaller bore and a larger stroke. For low revving engines, the piston has to cover a lot more distance for every stroke of the combustion cycle which is the primary reason for a lesser number of revolutions per minute. Also, since the bore on these engines isn’t too big, there is relatively less space for bigger, or more valves. The componentry of these engines is also on the heavier side, with weightier pistons, con-rods etc. Apart from the longer distance the piston has to travel, the heavier componentry is another reason for these engines being relatively lazy. The heavier componentry, however, contributes in producing higher torque lower down the rev range, making them very tractable even at ridiculously low revs. Retro styled, heavy cruiser bikes which are meant to be ridden at a relaxed pace and often lug heavy weight are more suited to this engine variety.
Advantages of low revving engines
• Low revving, long stroke engines are suited for easy-paced long distance cruising since they are relaxed in nature
● These engines are extremely tractable due to their healthy low end torque
● Low revving engines produce very healthy torque which is suitable for hauling luggage, making them excellent long distance, load-lugging tourers
● Low revving engines are generally more fuel-efficient as well, since they do not need to be revved a lot for making progress
● The long and heavy internal componentry of long stroke engines create a distinct beat which is often appreciated by old school cruiser motorcycle riders
The disadvantages of low revving engines
● Low revving engines have a poor top end performance, as the majority of the torque is produced lower down the rev range
● These engines have poor specific output, which means they produce much less power per unit of cubic capacity as compared to high revving engines
● Low revving, heavy engines are stressed when revved. Revving these engines hard for a prolonged period may even lead to engine damage
● These engines have a relatively smaller power band as the majority of the torque being produced lower down. As a result, they don’t accelerate very well above their mid revs. They also don’t have great acceleration or top speed
● Long stroke engines may not be as ‘fun’ as short stroke engines. They are not suited for track use
● Unless well-engineered, some low revving engines, with their heavier mechanical bits often vibrate more as compared to their short stroke counterparts, which benefit from lighter components and advanced technology
To conclude, high revving engines are lighter and make use of the latest technology to produce the most amount of power for any given cubic capacity. These engines are often used on high performance street bikes or sport bikes which are meant for track use. With high power reserved mostly in the higher band of the rev range, these engines like being revved and offer great acceleration and top speed. The negatives here include low tractability, low fuel-efficiency and a relative lack of load lugging capability.
Low revving engines on the other hand typically make use of relatively older technology, produce less power, but more torque, therefore being very suitable for cruising and touring motorcycles. Owing to their relaxed, easy-paced nature, these engines also offer better fuel-efficiency though it comes at the price of performance.
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