2500cc 4 cylinder and V6 which is more fuel efficient providing all other factors are constant eg driving habits roads etc?

All other factors being equal, a 2500cc V6 engine would generally be more fuel efficient than a 2500cc 4-cylinder engine. This is because a V6 engine has a more efficient combustion process and can produce more power with less fuel.

Here are a few reasons why a V6 engine is more fuel efficient than a 4-cylinder engine:

* Less friction: A V6 engine has a shorter crankshaft and fewer moving parts than a 4-cylinder engine, which reduces friction and energy losses.

* Better combustion: The V6 engine's design allows for a more efficient combustion process, with the fuel and air being mixed more thoroughly before they are ignited. This results in a more complete burn and less wasted fuel.

* More power: A V6 engine can produce more power than a 4-cylinder engine of the same displacement. This means that a V6 engine can operate at a lower RPM to produce the same amount of power, which saves fuel.

Of course, there are also some factors that can affect the fuel efficiency of an engine, such as the weight of the vehicle, the type of transmission, and the driving habits of the driver. However, all other factors being equal, a 2500cc V6 engine would generally be more fuel efficient than a 2500cc 4-cylinder engine.