Date:         Mon, 25 May 1998 13:48:02 -0400
Reply-To:     Martin Jagersand <jag@CS.YALE.EDU>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Martin Jagersand <jag@CS.YALE.EDU>
Subject:      Diesel Vanagons and Diesel engines.
Comments: To: vanagon@vanagon.com

To all diesel interested:

There are two VW diesel mailing lists. The most active one is:

vw-diesel@velocity.bc.ca

To subscribe send a message to wclistserve@velocity.bc.ca with
subscribe vw-diesel in the body. (Or see the link form my WWW pages
for digest alternatives etc.) The diesel list tends to be more
technical and to the point than vanagon, but people there are
every bit as friendly and helpful as on the vanagon and bus lists.

To have some content, here's my take on the recent diesel vs gas
discussion:

Reliability:

There's nothing inherent in the Diesel cycle that says a diesel
engine must be reliable. Diesel's have a good reliability reputation.
Two things contribute: The high compression (Typ over 400psi, vs about
100psi for a gas engine). To deal with this engineers typically
design thicker casts, use better bearings etc. This also makes the
engine long wearing. The other is the market. As someone already mentioned,
most of the market for diesels is in professional heavy equipment.
Professionals demand the best quality, and are less likely to fall
for marketing attempts to cover up poor engineering.

In case of the VW diesel, it was derived from the gas block, and
anyone who have worked on them can attest to that they look
virtually identical. To make it reliable, VW was conservative with
the displacement (stayed 1.6l for a long time, while gas versions
were 1.8 and 2.0), and used stronger casts, better bearings, head,
valves etc.

*Both* the gas and diesel engines are very reliable, and
the engines often far outlasts the car bodies. (This is the reason for
the plentiful supply of good used VW inline 4cyl engines).

The VW Diesel has the additional advantage over the gas of not having an
electical ignition system, electrical fuel injection and complicated
electic controls to meet exhaust requirements. These electrical
systems make up most of the complexity of an engine, and is a
common source of gremlins as the engine gets old and connections
get wet or corroded.

Power:

People still seem to have the misconception that horse power matters.
There's nothing with horse power per se. The problem is that HP is
specified at some high rpm and is irrelevant to 95% of all daily
driving. Torque is a better measure, and a torque curve over the
different rpm's the best. Torque is rotational force (ie ft-lbs,
how many lbs is pushed by a 1 foot lever). And force is what you
need to overcome wind drag, tire friction, and to push you uphill.

In most vehicles, 2500-3500 rpm is the rpm range the engine typically
works in. The 2.1 WBX has its torque peak (117ft-lbs) at 3400rpm),
in my opinion a bit too high rpm , but still a lot better than most
gas engines its size. The new Diesel (the 1.9l TD) I'm swapping into
my Westy has a slightly lower torque (110ft-lbs), but the good thing
is that the torque is available already at 2400rpm. The end result is
that for most typical driving I'll have more torque, which translates
(given identical gearing) into more forward force, better hill
climbing and acceleration etc.

Efficiency, Gas milage etc.

Better gas milage was the main reason we started seeing more diesel
cars and vans in the early eighties. Thermal efficiency measures how
much of the "heat energy" available in the fuel is converted into
mechanical energy. Typical modern gas engines are about 25% efficient.
Most diesels are 30-35% efficient -- Thats a whopping 20-40% better!,
and VW is already pushing beyond 40% on experimental Diesel engines.

This efficiency difference is the reason why for instance Diesel
Vanagons get 26-28mpg, while gas ones are limited to about 20mpg.

So in summary, while Diesel vehicles get the shorter straw when
comparing hp, they are still excellent and economic vehicles for
most daily uses. The 1.6 Diesel Vanagon is as good around town
as any other van, but goes at best 65-70mph on the expressways
(and the engine is really more comfortable at 55mph). So if you
want to go faster you would be better off with a 1.6 TD or 1.9l.

Happy VW-ing,
Martin
--
Martin Jagersand                 email: jag@cs.yale.edu
Computer Science Department             jag@cs.rochester.edu
Yale University

        Slow down and visit the VW diesel Westy page:
          WWW: http://www.cs.rochester.edu/u/jag/vw
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