Quote:
Originally Posted by needforspeed
Torque is the measureable rotational force which creates acceleration. You can ignore horsepower for the time being.
A vehicle will always accelerate hardest when torque at the wheels is highest. Torque at the wheels is a function of engine torque for a given speed multiplied by the effects of gearing.
BMW don't post in gear acceleration times for the 335d because it is only available as an auto. But it's in gear times WILL be faster than the 335i's, just as the in gear times for the 330d are faster than the 330i (in fact the 320d's are faster than the 330i).
This happens because turbo diesel engines create lots of torque, much more than petrol engines. Therefore most of the time, if you are cruising in a sensible gear - say at 70mph in 5th - the available wheel torque in a diesel will be greater than in a petrol car. That means it will accelerate harder in that gear - hence the in gear times.
The petrol car has an advantage though. It makes torque higher in it's rev range (which means it has higher horsepower). So in a 335i you would be able to drop to a lower gear than the diesel and hence multiply your torque.
So petrol cars ARE quicker, but only if you keep the revs high (in the powerband). You can't do this practically on the road, so in many situations diesels are quicker.
Great explanation here:
http://craig.backfire.ca/pages/autos/horsepower |
Great explanation Simon. I experienced this at UK3. Paddy's 320d (chipped) was very hard to shake off, he could accelerate as quick as me and stayed on my tail all afternoon. The only noticeable difference was when I was in the higher rev range (redlining
) and I would pull away slightly but change gear and Paddy would soon be back with me!