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Hi i have a question. Just wondering if the size of car affects fuel efficiency relative to the engine size.

Say for example you have a small car the size of a ford KA. It has a 1.4 litre engine and its quite good on mpg.

Now say you have a slightly bigger car the size of say a vauxhall astra also with a 1.4 litre engine.

would the KA be more fuel efficient because it it lighter and therefore less work needs to be done by the engine to move it a given distance?

assume driving conditions are exactly the same.

then again i suppose getting a bigger engine in a bigger car might not increase efficinecy because the engine components are bigger/heavier/take more fuel to start moving

can some 1 please clarify?

many thanks in advance.

If the engines were identical and fitted to two vehicles, one being lighter than the other, then the lighter vehicle will have a better power to weight ratio and as it has less weight to pull around it should have better fuel economy too (assuming the transmissions are identical too).

However, modern vehicles are a lot lighter as car manufacturers find ways to reduce weight. These days you can find 2.0L or 2.5L petrol vehicles with claimed combined fuel consumption figures closely matching smaller vehicles.

For instance, Mazda use SKYACTIV technology along with i-STOP in the 2014 Mazda 3 and fuel economy is claimed at 5.8L/100km (combined) for the 2.0L and 6.1L/100km (combined) for the 2.5L.

A 1.4L (non-turbo) engine will need to work a lot harder than a 2.0L motor up hills and during this type of driving terrain the 2.0L will likely use less fuel but in town driving (stop/start) the smaller engine should produce better results.