Umm, Hattie, it may not be any faster, since at 100 mph they are the same speed. It might be a little quicker 0 to 60mph, though.

Um, er, actually the I6 and the V8 both have to work as hard, since it takes pretty much the same horsepower to move either car at 70 mph. It's a question of how much fuel it takes to make the required horsepower.

http://auto.howstuffworks.com/question262.htm

Exerpted from the above link:

In a car traveling down a highway at the posted speed on level ground, the engine is doing three things:

1. It is overcoming rolling resistance in the drive train.
2. It is overcoming air resistance.
3. It is powering accessories like the alternator, the power steering pump and the air conditioner.


The engine might need to produce no more than 10 or 20 horsepower (HP) to carry this load. The reason why cars have 100- or 200-horsepower engines to is handle acceleration from a standing stop, as well as for passing and hill climbing. We only use the maximum HP rating for 1% of our driving time. The rest of the time, we are carrying around the weight and the friction of the much larger engine, which wastes a lot of energy.

All cars can cruise all day long at freeway-legal speeds. M-B's will do it in a certain comfort.

Our SDL's, or even the 67hp 240D, make quite enough horsepower to run down the highway. Oh, they may not make as much horsepower as the big gassers, and it therefore takes a few seconds more to reach cruising speed, but they use less fuel (25-30mpg instead of 15-17mpg) to make the required horsepower.

Hope this makes sense.

Best Regards,
Jim