[kaiser]

Originally Posted by SideValve

Always an interesting debate as to whether getting a car up to cruising speed quickly gives better economy than gently getting up to speed.

Obviously booting it drinks fuel but then you can back off sooner. Not booting it uses less fuel but then you spend longer getting into top and, as you journey takes longer, longer with your engine running & therefore burning fuel.

In theory you engine is at its most efficient when at maximum BHP (which is well up the rev range) but that's efficient as in juice vs power and once you are at the desired speed you don't need the power.

Maximum efficiency is not at max power but at maximum torque.