shift at 3k

[Fisher, Scott]

Nick (I *think* it was Nick) writes:

> Again, my question is whether the 'ruler flat' torque curve was engineered
> this way in order to spare the quattro system undue stress under hard
> acceleration (as my co-worker postulated?)

Your co-worker is misled.  The whole point of quattro is that the torque is
divided among four wheels instead of two.  In addition to the
well-documented traction and handling benefits that accrue, this also
reduces driveline stress on any individual driven wheel by a nominal 50%.
And I only weasel out with that "nominal" to account for the action of the
differentials, which split torque dynamically both front and rear and side
to side, so there's rarely an exactly equal distribution of torque.

But this is one reason why quattro-equipped vehicles can handle (no pun
intended) massive power increases without busting half-shafts and diffs as
readily as lots of other vehicles when you pump them way up.  Talk to
anybody who races Sprites in SCCA and you'll hear about heroic measures like
the ones we had to undertake (heavier axles, double-hub bearings, welded
diffs, and more) to keep from snapping the driveshafts up inside the diff
when you put 130 bhp into a chassis whose components were originally
designed for 48, especially when you mount 8" slicks on wheels originally
designed for 4" bias-ply tires.  (When you can manage to keep the axles from
breaking, however, the cars are a scream to drive that way -- I actually
used to rap my helmet off the roll-bar brace so hard on the upshift that it
hurt my ears...)  But -- doorhandles, window switches, and waterpumps are
popular items on the Q-list, but I don't believe I've ever heard someone
complain they'd broken a half-shaft from the extra power produced by their
newly-chipped turbo quattro.  (Quick, everybody, knock on wood! :-)

The ruler-flat torque curve is engineered that way because <tongue-in-cheek
degree="mild">magazine dweebs seem to think it's a good thing, and they've
brainwashed the tinted-windows-and-grapefruit-shooter-exhaust dweebs that
they should demand them in their cars, and car industry has learned that the
money of dweebs enriches the bottom line every bit as well as the money of
enthusiasts, and there's a lot more dweebs to pander to (witness the
popularity of the SUV).  I grudgingly admit that having a lot of torque at
low RPMs makes a car more predictable to drive, but where's the fun in that?
</tongue-in-cheek>

Seriously, though -- a flat torque curve does make a car much more
predictable to drive, especially in U.S. traffic which, by the standards of
many European countries, is generally congested and fairly slow.  U.S.
drivers put a high premium on being the first across the intersection, and
having an engine that develops much (if not most) of its torque under 2500
RPM is one way of achieving that.  In addition, a long research study by BMW
in the early 1980s -- leading to the eta series of engines, now discontinued
-- determined that fuel economy for a given engine displacement was best
achieved by optimizing the engine's operation for shift points at 2500 RPM.
In particular, they discovered that large throttle openings and 2500 RPM
shift points produced better fuel economy than small throttle openings and
5000 RPM shift points -- suggesting that it's the left foot, rather than the
right, which has the most significant impact on driver-dependent fuel
economy.

As for me, I rev the hell out of all my cars' engines.  One of my criteria
for a well-thought-out gearbox is that shifting at the redline should put
you into the fat part of the powerband in the next gear.  It's very
satisfying to get that push in the back when you make a hard shift into one
of the upper gears, especially.  There's a time for maximizing fuel economy,
and a time for maximizing its value. :-)

And I'll never forget the Road & Track report on the Audi 90 which, in one
paragraph, raved over the slickness of the shifter and then, in the very
next one, whined about how 5th-gear passing took too long because the engine
produced its best power over 4000 RPM or something.  How odd, I thought at
the time; the shifter in even my oldest Audi can select lower gears as well
as higher ones...

Best,

--Scott Fisher
  Tualatin, Oregon