One of the most important considerations when designing a good sports car engine is the power to weight ratio. Because a sports engine is all about rapid acceleration and responsive throttle performance, the power to weight ratio is a key factor. This is due to the fact that the heavier the vehicle the greater the power required to increase vehicle speed and acceleration.
When designing a sports car engine, it is good practice to keep the weight of the engine as low as possible. This can be achieved by using lightweight materials such as aluminum alloys for the cylinder heads.
Another way to increase the power to weight ratio in a sports car engine is to use turbo or super charging of the intake air. By force-feeding the intake air, 50% more fuel can be injected to increase the power output. This has the effect of a large power increase without any significant increase in the weight of the engine.
The best engine designers always consider the ratio of bore size to the length of the piston stroke. An over square shorter stroke sports engine is more suited to a high power output engine, typical of that used in sports cars. Another good example of this is in Formula One where engines with bore stroke ratios of less than 0.5 and running at 19,000rpm can be found. In road going sports car engines, however, the preferred ratio is normally around 0.8 with maximum engine speeds of around 7000-7500rpm.
One of the advantages of an over square sport engine, is that larger intake and exhaust valves can be used for better breathing at high engine speeds. This results in a higher peak power output. A superior sports car should have a shorter piston stroke. This provides a shorter travel distance per stroke, so maximum piston speeds are lower. This means that higher maximum engine rotational speeds can be obtained for higher maximum power output. All of these factors significantly contribute to an increase in a sports car engine’s power to weight ratio.
The second most important consideration in a sports car engine is to keep its centre of gravity as low as possible. As the engine is one of the heaviest individual components in a sports car or sedan car, if its centre of gravity and its mounting within the body can be kept as low as possible, it has a very significant effect on the sports car’s overall centre of gravity.
The best sports car engines have a low centre of gravity because of the cylinder layout configuration. For example, many manufacturers such as Honda have used a ‘V’ engine layout in their sedan car because it has a lower centre of gravity. A horizontally opposed boxer engine is the best configuration for a low centre of gravity. The Subaru WRX STI is a sports car that uses boxer engines for this reason.
A low centre of gravity is essential in a sports car to minimise weight transfer from the inside to the outside wheel when cornering.
A high performance sports car engine design can therefore not only increase acceleration control but also significantly contribute to the handling of the sport car, resulting in a safer car that is more fun to drive.
