German Car Zone

One thing I haven't been able to find an answer to is this: would a 2 Litre V12 (think old time Ferrari) have the same gas mileage as, say, a 2 Litre 4 cylinder engine?

Conceivably they would, especially given that their displacement over a period of time 'could' equal out. If one piston going around the crankshaft equals 1 rpm in the 4 cylinder engine, and three cylinders (firing simultaneously or in sequence) make up 1 rpm in the V12, then they would both end up taking in the same volume of air/fuel, and so consequently use the same amount of fuel per mile....right?

Any engineers out there?

Interesting question.

It would be kind of hard to figure out since one is an economy engine the other would be more high performance.
It would be easier to look at a 2.3 liter 4 cylinder and a 2.3 liter 6 cylinder.

I think the V12 would use more fuel.

Yeah, I still have no idea

Well, even with only 2 litre the engine of the V12 has to move 8 (!) cylinder more then the little 4-cylinder engine. Probably it bruns more fuel then - but I really have to say, that I'm not very technical capable!

I think I can answer your question.

A 2L V12 will be extremely inefficient because of the low volume to surface area of the cylinder, so what you end up is excessive heat loss to the cylinder wall, and the thermal efficiency of the engine will be poor. Also because the cylinder is too small, you can not really inject useful amount of fuel to get useful amount of work done. Also because of the small cylinder, circumference will be too small to place a 4 over head valves above the cylinder. The volumetric efficiency of the engine will be reduced, and the combustion will not be optimised.

The most efficient cylinder size is 500cc, and a lot of high performance car engines have that specific cylinder size, eg the 6.0LV12 from BMW, the 8.L W16 from the Veyron, and a 2.L 4 cylinder engine from various manufacturers.


For engine analysis, we analysis each cylinder individually, and not all together, and fuel consumption is measured in kg/s. A 2L V12 will be too inefficient to achieve the same mileage as a 2L 4 cylinder. Feel free to ask me more questions.

So what about a 2.3L 4-pot vs 2.3L 6-pot as Gullwing suggested, or 2.0L 4-pot vs 2.0L 5-pot?

I'd love to read your comments!

^ Right on Monster... there's your answer folks.

Giannis, the differences in specific volume per cylinder is much less dramatic between 4, 5 and 6 cylinder engines than in the example of a 2.0 litre 4 pot vs a 2.0 litre V12.

These differences can be compensated for in the mechanical construction of the engine (for example by shortening the stroke) but it doesn't change the fact that the generally acknowledged optimum cylinder capacity is 500cc.

Sure Martin, but why some most manufacturers choose 4-pot 2.0L engines, while Volvo chooses 5-pot ones? There must be some advantages and dissadvantages.

A friend suggested that the stroke is smaller than the stroke, the engine revs more easily, but is a bit less efficient than an equilevant 4-pot! This is because the pistonheads travel less..

In what way is a 4-pot 2.0L more efficient than the Volvo engine? I am not too familar with volvo engines, but if I remember correctly, they are 2.5L units? There are all sorts of things a car manufacturer considers before determining the power output of their engines, so it is hard to tell the true potential of each engine.

In general, the efficiency of the engine in general is more affected by the actual mechanical design, and component design rather than the number of cylinders. However they are all related to each other in some ways.