In a message dated 1/17/02 3:35:39 PM, NotaJeep@AOL.COM writes:

<< Let's say 50 mph (breakneck in a diesel westy) takes 5 HP...IF the engine
can
develop that 5 hp though a combination of available torque and rotational
speed then the van maintains speed...Now it may take ALL the torque that the
engine can produce at the "50 mph" rpm..fine..don't plan on passing..you,
friend, have hit terminal velocity under those conditons...fine..IF you are
PAST the rpm of max torque then you can gear UP and accelerate! it's known as
"torque back" (spent many an uphill mile with my eyes glued to the tach on a
220 Cummins so I knew when to shift UP to make the pass) >>

Steve,

I would have replied earlier, but my typing finger developed a case of
frostbite when I used a Freon Cold Spray to cool down my overheated
calculator!

"Just the facts, nothing but the facts" as was once said. (I think Maam goes
in the original quote but its clearly inappropriate for this citation).
Buttochian accelerometers be banished!

At 50 mph, level road, calm air, the basic Westfalia requires just over 26.8
brake horsepower (20 kW) to maintain velocity (Martin Jagerstand's
measurements). With the DZ transmission in 4th gear this translates to the
need for 41.4 foot-pounds of torque to move the vehicle. With the air-cooled
transmission gearing, this number (required torque at the flywheel) becomes
53.2 foot pounds. The maximum torque delivered by the NA Vanagon diesel at
3400 rpm (DZ trans, 4th, 185SRx14 tires (821 revs/mile), 50 mph) is 71.5 foot
pounds. At 2657 rpm (4.57 final, 4th, 185SRx14 tires, 50 mph) the maximum
torque available is 75.2 foot pounds.

Therefore, at 50 mph with DZ gearing (5.86) the hapless voyager has a reserve
of 30.1 foot pounds of torque to squander on such issues as additional mass,
headwinds, positive changes in altitude, frictional losses due to surface
liquid layers, reductions in atmospheric pressure and (thrill) attempted
velocity changes (often called acceleration in gas or TDi powered vehicles.
In the case of the 4.57 final drive AC trans, this surplus becomes 22 foot
pounds (a reduction in available force of 27%). Looking at the problem from
the other side of the tunnel, the 5.87 gearing has more that 40% the surplus
force available as compared to the 4.57 option. Both clearly can maintain 50
mph.

Studying the torque and drag curves, both gearing systems predict a similar
top speed Westfalia, level, calm, etc, etc). 62 mph for the DZ trans and 61
for the DK. Here I define top speed as the point at which maximum available
thrust is equal to total drag.

So, Steve is right, for a 40% drop in marginal performance, the DZ or DK
transmissions can both support locomotion of the Westfalia. Of course, many
have concluded that the discretionary motive force available with the
standard gearing was already pitiful, but you makes your choice.

BTW, all these details including the torque curves, gearing issues,
longevity, etc. have been placed in the archives by myself and others in the
not distant past

Frank Grunthaner