Oh my . . .
You need BOTH. Torque at the wheels is what you'll FEEL. This is a hot
topic among car enthusiasts, some will say HP, the others TQ. I'll try to keep
this fairly (HA!) short and relevant to Roadsters. Think of a 1600 Roadster
with a built 1600 that makes 150hp. We also have a stock 2000 (Solex) Roadster
that also makes 150hp. The 2000 will have more torque due to it's increased
displacement (for this arguments' sake). They both happen to weigh the same,
same tranny, tires, and axle ratio (eliminating variables here). Run them in
the 1/4mi, 0-60, etc, there will be little difference in ET and MPH. The
launching techniques for the 1600 will be to rev the motor higher than the 2000
at launch to equal it's times. Same HP & weight, etc will give equal
acceleration times 99% of the time. This is HP at work.
Now they're driving around some hilly (I said HILLY, not HILLBILLY :-)
backroads. The 2000 will just motor up hills without downshifting as much as
the 1600 even thought the HP is the same. Or they're side by side at 60mph in
5th, and they both floor it. The 2000 will pull away initially. This is torque
at work. Where you don't have torque, you can make up by gearing and RPM's.
(meaning downshifting the 1600 will even things up)
Riding in these Roadsters, the 2000 will *FEEL* faster, even though their
acceleration munbers are the same - this is torque at the drive wheel. The 2000
basically pulls harder for a shorter period of time, the 1600 pulls weaker, but
longer in each gear, so it averages out. (I can explain this in another letter
if need be).
Notice that cars with high HP but small displacement (read, relatively low TQ)
have shorter (higher numerically) axle ratios - this is to "make up" for less
torque by using gearing to muliply engine torque to the wheels. A 300ZX
(198ft-lbs, 222hp, 3300lbs) has 4.1 axle ratio - runs low 15's in the 1/4mi. A
Mustang GT (275ft-lbs, 215hp, 3300lbs) has a 3.08 axle ratio.and also runs low
15's in the 1/4mi. Doing math - at the crank the ZX has 69% of the torque of
the GT, but after the axle ratio is factored in, it has 95% of the GT's torque
to the wheels (assuming same tire size, another story).
Hit this link http://www.datsuns.com/techmenu.htm, under general tech hit :
"Horsepower defined and explained". Also see "Gearing and its effects".
This should make it as clear as Clinton's definition of "is".
Dave Lum
'71 510
http://www.datsuns.com - for all your technical needs
-----Original Message-----
From: Ian Miller [SMTP:ianmiller9@hotmail.com]
Sent: Wednesday, January 20, 1999 10:16 PM
To: davelum@datsuns.com; datsun-roadsters@autox.team.net
Subject: Re: Roadster diffs & torque
So how do Torque and HP affect performance. Which one gives you better
acceleration ect.?
|