Efficiency Battle: Are Bigger or Smaller Engines More Fuel Efficient?

When it comes to fuel efficiency, the debate between bigger versus smaller engines is ever-present. However, the answer is not as straightforward as one might think. It is highly dependent on how the car is used and the driving conditions.

Engine Size and Fuel Consumption in Different Driving Conditions

A smaller engine, such as a compact car's engine, operates closer to its most efficient load and speed for daily driving around the city and suburbs. Its fuel consumption tends to be minimal, as it is designed to work at lower speeds and loads. However, when these smaller engines are operated at higher speeds or under heavy loads, such as driving on the interstate at 80 mph, their efficiency decreases significantly. At such speeds, smaller engines struggle and consume more fuel because they are not optimally designed for these conditions.

In contrast, a larger engine, especially on the interstate, operates more efficiently at higher speeds. For instance, a 212 kW engine in an Audi can consume as little as 6 to 7 liters per 100 km in highway conditions, whereas a smaller engine in a car like a Mazda might consume 9 to 10 liters per 100 km under the same conditions. This stark difference highlights how the type of driving and road conditions affect the efficiency of the engine.

Examples from Different Vehicles and Scenarios

A 2018 4.3 V6 Silverado, for example, routinely achieved 26-27 miles per gallon (mpg) on the highway, especially when it was properly fitted with 3/5 descents and stock tires. Another example is a 2019 Silverado with a 2.7-turbo engine that barely achieved 22 mpg on the same type of tires. This disparity can be attributed to the engine's capability to match the load during operation. The 2.7-turbo engine lacks the horsepower to maintain efficiency under part-throttle conditions.

Similarly, when comparing the fuel efficiency of a 3.5 V6 Charger to a 5.7 Hemi Magnum, the 3.5 V6 consistently exhibited better fuel consumption by 1-2 mpg. This was primarily due to better load matching. Smaller engines, when properly designed, can optimize fuel efficiency even in larger vehicles.

Factors Contributing to Fuel Efficiency in Smaller Engines

Smaller engines exhibit several optimizations that contribute to their greater fuel efficiency. These include:

Reduced Friction: Smaller engines have fewer parts, which leads to less friction and less energy wasted. The reduced friction makes these engines more efficient, especially at idle speeds. Better Weight Distribution: Smaller engines, coupled with lighter and less bulky vehicles, contribute to less power consumption. A 2-liter 4-cylinder engine generates half the friction of a 4-liter 8-cylinder engine, leading to lower fuel consumption. Smaller Frontal Area: Lighter vehicles with smaller frontal areas require less power to move and push through the air, leading to improved efficiency.

In conclusion, the debate over whether bigger or smaller engines are more fuel efficient is multifaceted and highly dependent on the driving conditions. While smaller engines can be more efficient for daily city driving, larger engines offer better efficiency at higher speeds on the highway. The key is understanding the specific needs of the vehicle and the driving scenarios.