Things finally calmed down enough after the Pro Solo that I had a chance
to read the article on torque and power ...
Jim Muller writes:
> >For your purposes, ignore the difference between torque and horsepower.
> >There isn't any. They're just different ways of expressing how the engine
> >produces results... Most people who talk about "horsepower" and "torque"
> >talk as if they're two different things, like downforce and camber. That's
> >nonsense. They're two ways of quantifying how an engine produces results.
>
> Quite incorrect, even for his purposes. While both may be a facet of "going
> fast", they are very different, and a proper understanding of the issue
As a matter of fact, the article didn't convince me of this -- I still
feel that they're basically different ways of expressing available
"results" from the engine. Note that I agree that *peak* power tells
you something different from what you learn from *peak* HP; however,
if you know the power *curve*, then you also know the torque curve,
and vice versa.
> >> I guess the question boils down to: What does an increase/decrease
> >> in HP or Torque do to the 'seat-of-the-pants' feel of driving? How
> >> will it effect the off-the-line speed, passing speed, etc?
I would be inclined to answer this question simply:
Changing the *shape* of the torque curve (which also changes the shape
of the power curve, since they are linearly related to each other)
will produce a significant change in seat-of-the-pants feel, even if
you don't change the peak torque or power. Changing throttle response
has an even greater effect than changing the power curve. Seat of
the pants is extremely unreliable in judging performance (Bill Condrashoff
has been trying to tell me this for six months, but I didn't believe him
until last month when someone lent me a Vericom and I discovered that
my seat-of-the-pants jetting was losing me about 5HP).
> For these reasons, a slight tradeoff of less maximum power for lower-rpm
>torque
> can be beneficial even though it really is *power*, not torque, (and actually
> power per weight but we have been assuming equal weights) that you need.
I'm not clear on why you say that it's power, not torque, that you need.
You need power because moving the car takes work. On the other hand, the
way you move the car is through forcing the wheels to rotate, which requires
torque. It's two different ways of expressing the same concept.
> must still be considered. For brute-acceleration (1/4 mile and 0-60 times, or
> for autocrosses) then lower rpms (actually higher running gears) is desirable,
> so equal power but obtained at higher rpms is not as good.
I must have missed the explanation of why this is true. Well, maybe you
have to slip the clutch more if you have to use higher gears to accelerate;
or is it because of what you said earlier about rotating inertia of the
flywheel and so forth (i.e. you would have to have a more powerful engine
to get the same acceleration if the power curve was slanted toward higher
RPM)?
> two engines with equivalently state-of-the-art breathing, torque is directly a
> function of displacement, so with a limited displacement, you have a limited
> torque. So to go faster and to get better acceleration, especially when top
> speed is important as in a race, manufacturers typically have no choice but to
> move the torque peak up to higher revs, getting more power. As long as the
I don't understand why this is, either. Why is torque a direct function
of displacement? And what do you mean by "breathing"? Is compression
ratio a part of "breathing"? Doesn't compression ratio affect power
and torque?
And what affect does oversquareness have on power and torque?
Hmm -- thinking about it a bit, I might be willing to believe that
bore/stroke doesn't affect power, all other things being equal. Short
stroke makes an engine rev quicker, I know that; I would think that it
would change the power curve to weight it toward higher RPM, but I
can't find any convincing logical argument for this, so maybe it's wrong.
Does it change the power curve, e.g. does higher bore/stroke lead to
higher (power peak)/(torque peak)?
--
...Akkana akkana@eeg.com
SAM Technology, Inc. {pacbell,lll-winken,ucsfcgl}!eeg!akkana
|