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Date:         Thu, 17 Jan 2002 21:36:46 EST
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: Yer torquin me....<grin>
Comments: To: NotaJeep@aol.com
Content-Type: text/plain; charset="US-ASCII"

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


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