Let me suggest that your statement is more theoretical than practical.
On the street, you want torque.
If you are a Nascar racer on the track, you want horsepower.
Randy
On 29/07/2014 7:34 PM, Fmiser via Mercedes wrote:
OK wrote:
IIRC, the V8 has more torque, which is what a truck needs.
Well, no. Not really. But sort of.
Nothing against you Don, but this is a very common
miss-perception. So I'm not picking on you - just using your
comment as motivation to respond. *smiles*
Torque is rotational force. There can be torque with no movement.
Unless there is movement, no work is being done.
If there is torque, and movement occurs - then work is being done.
With a stopwatch (or calendar?) you can measure how fast the work
is being done. This is horsepower [or watts].
If you have an engine with a fixed horsepower attached to a
transmission (presuming an infinite ratio and lossless - which
doesn't exist) the torque can be any value at all. For high
torque, it will be moving slow - but for low torque it will be
moving fast.
If we don't change the diameter of the tire, the torque on the
axle necessary to pull a 4000 lb [1800 kg] trailer up
Grapevine out of Los Angeles is fixed. So if your your 400 hp
pickup and my 7 hp garden tractor have the same size tire, the
torque needed is the same. The difference is speed. Your
pickup will get to the top a lot faster than my tractor
because the axle can turn faster because your engine has more
horsepower.
So far it's very clear - but then reality rears it's ugly
head. Transmissions have fixed ratios and losses. Engine
ratings are for _maximum_ horsepower - but the actual
horsepower and torque vary depending on speed. This makes it
almost impossible to actually do an apples-to-apples
comparison.
Nevertheless, looking at the torque value is pretty
meaningless. If you look at the torque values for various
engine RPM, you can get a clue as to how usable the
power is. If there is little torque at low RPM, then high RPM
will be needed to get useable power. This makes it feel like
the driver has to work the engine harder to get the job done.
So - to repeat. Just a torque value is nearly meaningless.
Torque at a particular RPM is useful - but that is by
definition horsepower!
-- Philip
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