scott ) gurgled happily, sounding much like they were
saying :

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.

Yet the bigger engine may well be running at much lower load.

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.

Not so. It's far easier to make a large car more aerodynamic than a short
one, both in terms of pure aerodynamics and in terms of packaging. Frontal
area comes into play via CdA, but there's not that huge a difference
between the frontal area of a short car and a long one where both are
required to offer similar interior space, as the long car doesn't have to
be as tall.

In short, it's impossible to say.