Quote:
Originally Posted by MaestroAl
Actually, I think I understand what you meant by "performance indicator". Inasmuch as a higher bhp figure is an indication that a car develops high torque at high rpm then yes, it is a good indicator of "performance".
But let's not forget that this is all in the context in which it was intended. The rate of acceleration is only ever governed by torque. Ever. The rate of acceleration is what makes a car feel quick to the driver, it is all we're aware of in terms of straight line performance as a driver. A car like the 30D will always feel quick in any gear whereas cars like the 335i and M3 will never "feel" as quick because they can never have the same amount of torque applied to the drivetrain. Thanks to gearing, they will be empirically quicker when driven in the higher rev ranges where they shine and as I've always said: they'd leave a 30D behind but again, nobody drives like that in the real world and they have to be driven like that to be as quick as a 30D - and will never feel as quick unless you're booting it at 7000rpm in third or something: an experience you can't match in a diesel.
So since these kind of cars require effort, revs and a lot of fuel to match the 30D's performance and even more to surpass it, in the real world of on-road driving, the 30D is the quicker car and torque is more important than horsepower.
QED  |
Hmmmmm, it is a complicated issue this hp and torque thing.
(To explain it I think of the following)
Whilst true that torque is the rotating dynamic that dictates ultimate force levels, it is horsepower that we are interested in. Torque is a rotational force and horsepower is the same force expressed in a linear form. Horsepower is easier to grasp if we imagine that there is a drum attached to the flywheel, and we use that drum to wind up a rope (linear movement). The torque determines the force of pull on the rope, horsepower determines the rate at which the end of the rope moves, the faster the drum, the faster the rope.
Now you can debate till the end of time which is more important, but remember that gearing determines the torque applied to the wheel, and that is the single most important factor, more important than the torque developed at the flywheel. We can trade low flywheel torque for high wheel torque and vice versa.
Now if we go back to an engine driving a drum with our rope. Imagine instead of laying the rope on the ground we hang it over a cliff and add a weight to the end of it. A 330D could pull a large diameter drum but at low revs (high torque/lowish power) versus a F1 engine which because it doesn't have much torque, would have to have a small diameter drum attached to it to pull the resistance in our rope, but because it can rotate the drum at very high speed, will win the race.
A torque/gearing chart comparing 335i vs 330D would be very interesting