Date: Sat, 27 Oct 2001 14:24:27 -0700
Reply-To: mark drillock <drillock@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: mark drillock <drillock@EARTHLINK.NET>
Subject: Transmission Ratios, Diesels, Conversions
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Frank, I guess it all depends on which set of engineers you have an
affinity for. Look at the gearing choices of the VW engineers who
actually were responsible for putting the gas inline 4 engine into
production Vanagons. Don't expect to see 4 speeds with diesel r+p ratios
(5.83, 5.43). They did NOT choose such low gearing. I believe 4.83 is
what they mostly used, a waterboxer ratio. Also offered 4.57 AFAIK. Were
they brushing aside their own engineering data?
And yes, if a mere 60 mph is your intended highway cruising speed then
the diesel r+p ratios are useable. I just got back from a 1200 mile
interstate trip in my 4.57 r+p TD Vanagon. I did not see any passenger
vehicles traveling at such a low speed except uphill. Who in God's name
would install a Tiico conversion and then drive at such obstructionist
speeds on long trips? Only a masochist would hold 60 mph for hours on I5
with semis constantly running up their butts at 70 mph. "The most
efficient utilization of an engine" is not always the primary
consideration. Sometimes real world factors interrupt the dreaming.
Mark
Frank Grunthaner wrote:
> ..............
> Even though I'm in complete agreement with Alistair Bell's latest post, this
> discussion about the obvious undesirability of the diesel transmission for I4
> engine conversions has still stimulated my latent hemorrhoids again. And
> while I suspect that the majority of the adherents to this pseudo-wisdom will
> brush aside engineering data as simply obscuring the real understanding, I
> will try again to offer a few terse (really!) comments.
>
>.............
> Final observations. If you don’t trust the engineers, go reduce the
> longevity, minimize the performance of your conversion and gain almost half a
> mile per gallon by swapping in the 4.57. Otherwise, enjoy the performance of
> the 5.86. These observations are really due to the relatively unique design
> of VW’s I4 engine family. The torque curve is nearly flat (as compared to the
> highly peaked performance of American Iron and Japanese spinners). This
> indicates that the volumetric efficiency of the 8V engines is a very minor
> function of rpm. The 1.9L WB is much more peaked. Much of this comes from the
> cam and the intake runner design. The 16V VW engines also have strongly
> peaked torque curves.
> ...............
> The most efficient utilization of an engine is attained when its torque
> maximum is achieved at the most desirable operating condition. From my
> perspective, cruising in top gear at 60 mph is pretty close to a good optimal
> operating condition. So, for the 2.0L Air Cooled engine, the 4.57 trans is
> ideal with stock skins. For the 1.8L Digifant, the optimum would be the 5.43
> regular diesel trans with 215/75x15 tires. The 2.0L I4 would be best with the
> 5.86 trans and stock tires, while the 2.0L Turbo is well matched to the 4.57
> transaxle with 215/75x15 wheels/tires.
>
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