How come we never see HP/weight ratios? Wouldn't that me more accurate in determinig power of a car?
11-06-2002, 08:33 AM
#5
Member
Join Date: Dec 2001
Posts: 3,468
Likes: 0
Received 0 Likes
on
0 Posts
No single stat can summarize a car - HP can be pretty misleading
You're right that an engine's capability needs to be judged relative to the mass of the car it has to lug around. But instead of HP, engine capability is perhaps best captured by looking at the torque curve of the engine. After all, HP is mathematical function of engine speed and torque.
Torque is rotational force, and from Newton F=Mass X Acceleration. Mass is a key factor, as we all know.
HP is power, or rate at which work is done.
Work = Force x distance
so,
power = (force x distance)/time
or
power = (mass x acceleration x distance)/time
It's hard to make this intuitive, but HP is the rate at which the engine can deliver force to accelerate the car.
If you want to pull stumps out of the ground - get a big diesel with huge torque. However, those engine's can't deliver that force quickly (that is, torque falls off as engine speed increases), so the HP numbers from those engines are underwhelming, and the trucks aren't particularly fast. Still, non-technically speaking you'd call that a "powerful" engine.
The flip side is the S2000 or M3 engine. Torque levels are not particularly impressive, but they can deliver the force quickly (that is, the engine still outputs good torque levels even at very high engine speeds, as reflected by the high redlines) and it makes for a FAST car and impressive HP numbers. But you'd never be able to pull a stump like with a big diesel, since an S2000 can't deliver all that much torque.
Since HP and torque interplay to determine how "powerful" a car feels, you can't use either number to capture that feel. The best compromise is probably looking at the torque curve and, as you said, considering the total mass the engine must move around.
Torque is rotational force, and from Newton F=Mass X Acceleration. Mass is a key factor, as we all know.
HP is power, or rate at which work is done.
Work = Force x distance
so,
power = (force x distance)/time
or
power = (mass x acceleration x distance)/time
It's hard to make this intuitive, but HP is the rate at which the engine can deliver force to accelerate the car.
If you want to pull stumps out of the ground - get a big diesel with huge torque. However, those engine's can't deliver that force quickly (that is, torque falls off as engine speed increases), so the HP numbers from those engines are underwhelming, and the trucks aren't particularly fast. Still, non-technically speaking you'd call that a "powerful" engine.
The flip side is the S2000 or M3 engine. Torque levels are not particularly impressive, but they can deliver the force quickly (that is, the engine still outputs good torque levels even at very high engine speeds, as reflected by the high redlines) and it makes for a FAST car and impressive HP numbers. But you'd never be able to pull a stump like with a big diesel, since an S2000 can't deliver all that much torque.
Since HP and torque interplay to determine how "powerful" a car feels, you can't use either number to capture that feel. The best compromise is probably looking at the torque curve and, as you said, considering the total mass the engine must move around.
Thread
Thread Starter
Forum
Replies
Last Post