Redonda wrote:
scott wrote:

How do you work that one out? If I'm using more power to go faster,
surely I need to be using more petrol? As air resistance increases
with speed squared, the amount of petrol used goes up quite quickly
once you get to higher speeds.

As I've said before, it depends on the car/engine. My top speed is
130mph (not had it above 120 - but still plenty of puff left), so at
motorway speeds it's running around 4000rpm (80-ish) with virtually
no throttle applied. A smaller engined car will usually not have
much in hand at those speeds - notice what happens when a small car
starts to overtake at the bottom of a hill. It will usually run out
of power and drop back.

Same in town. Smaller engined car drivers are up and down the
gearbox to make progress at speeds varying from 10 to 30mph where I
can stay *comfortably* in 3rd gear through all that range without
creating huge gaps or having to brake sharply.

So. Whose engine is working harder?

Well assuming both drive the same speed, the bigger car is probably
generating more power as it has to shift more weight around. Assuming both
engines are equally efficient, the bigger car is therefore generating more
pollution. At constant speeds the power will be closer matched, although
the bigger car probably has more drag, so again, bigger car makes more
pollution.