Small can be good, especially when it comes to the engines that power our vehicles. With the price of fuel continuing to rise, automobile manufacturers are looking to build more fuel-efficient vehicles, and installing a small-displacement engine is one way of improving fuel economy: it simply takes less air and fuel to fill the smaller cylinders.
There are other advantages to small engines. They are lighter, and this helps both in fuel economy and in performance. Light engines allow many other parts of the vehicle to be lighter too: suspension parts such as springs, sway bars and control arms don’t need to support as much weight, so they can be lightened. Smaller engines need smaller cooling systems, reducing the amount of coolant in the vehicle. More fuel efficient engines can operate with smaller fuel tanks while still getting good driving range. Gasoline weighs about 800 grams per litre. Reduce the fuel tank from 80 litres to 50 and you now have 24 fewer kilograms of weight to accelerate or brake. Every little bit of weight reduction helps: for every 45 kilograms of weight you remove from your vehicle, gas mileage can increase by one to two per cent.
Small engines also improve vehicle performance. It is easy to recognize that a lighter vehicle accelerates faster – just look at motorcycles as proof of that. What many forget is that a lighter vehicle also brakes quicker. On the race track, it is usually the driver that can carry speed further into a corner and brake harder that will be able to pass. While I would definitely not recommend this technique on the street, being able to brake harder does provide additional safety.
Handling is also enhanced: lighter cars turn corners easier. On a race circuit, it is the more nimble small-displacement-engine cars that can run circles around the big block cars, except on the straights. When it comes to straight line acceleration, they have said there is no substitute for big displacement engines, but even that concept is changing.
Turbocharging is one of the ways of providing big displacement power in a small engine. Look at Ford’s EcoBoost engines, the Chevrolet Cruze turbo, almost any Volvo and the Hyundai Sonata Turbo. These vehicles along with many others use turbochargers to make the engines more efficient. In the past, an engine was performing well if it achieved 80 to 85 per cent volumetric efficiency. This means that the cylinders are filled with the correct air/fuel mixture to about 80 per cent of their capacity. Because gasoline engines operate over a wide RPM range, it is difficult to make them as efficient as an engine that operates at a constant speed. Variable valve timing, tuned intake manifolds and free-flowing exhaust systems help, but even race engines have difficulty achieving more than about 95 per cent efficiency.
The turbocharger changes all that. A turbocharger is an air compressor driven by the exhaust gases of the engine. By compressing the intake air above atmospheric pressure, the cylinders can hold more air than they would even when the engine is stopped. By pressurizing the air, the volumetric efficiency increases to over 100 per cent and the engine has a lot more power. Turbochargers convert the wasted energy of the exhaust gases to produce more power. A small engine can feel like it has the torque and power of a big one, and the best part of this is that the turbocharger only provides the extra power when the driver asks for it by stepping on the accelerator. The rest of the time, the turbo is idling along at about 20,000 to 30,000 rpm, producing no boost and allowing the engine to sip fuel miserly. Turbocharging is one of the most efficient ways of increasing engine power and you can expect to see it used much more in the future.
Some say there is no substitute for big displacement power, and that may be true if you are pulling a big trailer or going to the dragstrip, but the majority of drivers who use a vehicle for personal or family transportation would rarely use that type of power. Small is best for fuel economy and handling and the current generation of small displacement cars show that they can be fun to drive, as well as economical.
