Date: Sat, 30 Mar 2002 08:15:58 +0800
Reply-To: Kim Howe <khowe@OMNINET.NET.AU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Kim Howe <khowe@OMNINET.NET.AU>
Subject: Re: On Longevity, Displacement,
Efficiency and Technology in Conversions
Content-Type: text/plain; charset=US-ASCII; format=flowed
From: Kim Howe <khowe@omninet.net.au>
Date: Sat Mar 30, 2002 07:05:30 AM Australia/Perth
To: FrankGRUN@AOL.COM
Subject: Re: On Longevity, Displacement, Efficiency and Technology in
Conversions
Frank, I really enjoy your posts, I wonder if you could clear up a
couple of things for me.
On Tuesday, March 26, 2002, at 02:58 PM, Frank Grunthaner wrote:
So, lifetime of any modern engine is directly related to the work you
require
that it generate during your ownership period. Period.
So, if for example the Vanagon and a Golf had the same engine, and the
same gearing, and spent most of their time traveling at 75mph, the
difference in engine life would be the relative drag (aerodynamic and
otherwise) between the two, ie if the drag of the Vanagon is 3 x that of
the Golf, and the engine will do 300,000 miles in the Golf, it will do
100,000 miles in the Vanagon? Do you know where we could obtain the drag
figures for the different vehicles to evaluate this?
o, anyway, I decided to prepare a table that could compare the
mechanical
efficiency (and therefore engineering prowess) of the various engines
that
could power these bricks through the ether. The quantity of comparison I
have
chosen is the brake mean effective pressure developed in the combustion
chamber while doing work on the piston. The number is derived from the
peak
torque developed at the flywheel per unit engine displacement. These
numbers
are readily calculated from the meager engineering data provided by the
reclusive Subaru personnel, and are readily expanded by the addition of
your
favorite heat pump. I have arranged the values in ascending order of
higher
pressure (means higher efficiency). Pressure expressed in units of psi.
In
essence, the torque maximum represents the peak volumetric efficiency of
the
pump as well as the maximum efficiency of completely consuming the
available
fuel for air heating. This number is a function of the combustion chamber
design, the intake and exhaust manifold flow dynamics, cam and ignition
timing, etc.,etc. Bigger is better. (Also often newer.)
If I were to put an aircooled engine on a dyno and read off the torque,
I would be reading the torque including all cooling system losses. If I
were to do the same with a liquid cooled engine, I would be excluding
the drag introduced from the radiator, and probably make sure I got my
readings before the fan cut in, so I excluded the alternator drag from
that too. Did you compensate for this at all? Do you know of any way to
calculate these losses? It would be interesting to see a comparison of
the total cooling system power requirements for air cooled and water
cooled engines. I remember seeing this done many years ago, and the air
cooled won hands down, which was behind my statement that aircooleds are
more efficient (ie air cooling wastes less energy). Liquid cooling
technology may have improved enough in recent years to make this no
longer the case. (Or was the information I saw years ago in error
anyway?)
Engine Displacement Torque BMEP
(liters) (ft.lb.) (psi)
Vanagon 2.0L A/C 101@3000 126.9
VW GX 1.8L I4 96@3000 132.8
VW MZ 1.8L I4 98@3250 135.6
Vanagon 1.9L WB 106@2600 136.6
Subie 2.5 2.5L WB (<96) 144@2800 136.6
Vanagon 2.1L WB 117@3200 136.7
VW 9A 1.8L I4 113@4400 140.8
VW HT 1.8L I4 105@3000 145.3
AUDI 2.3 2.3L I5 140@4500 149.7
VW RV 1.8L I4 109@3800 150.8
Audi 3A 2.0L I4 121@3200 150.8
VW ACC 1.8L I4 107@3500 150.8
VW AAZ 1.9L I4 TD 107@2500 150.8
Subie 2.5 2.5L WB (>97) 162@2800 150.8
Subie SVX 3.3L WB 228@4400 150.8
VW ABA 2.0L I4 122@3200 152.0
VW RD 1.8L I4 110@3200 152.2
VW AAA 2.8L I4 173@4200 152.6
Subie 2.2 2.2L WB 137@4400 153.0
Subie 2.5 2.5L WB P II 166@2800 157.4
VW PF 1.8L I4 114@3800 157.7
SAAB 2.0 2.0L I4 128@3000 159.5
TIICO (SA)2.0L I4 132@3500 164.5
Subie 2.2 2.2L WB P II 149@3600 166.4
VW AHY 1.9L I4 TD i 149@1900 193.7
VW 1.9 TDi1.9L I4 TDi 155@1900 201.5
Subie 2.2T2.2L WB T 181@2800 202.2
VW 1.8T 1.8L I4 T 162@2200 224.1
SAAB 2.0T 2.0L I4 188@3000 234.3
If there were unreported losses in the water cooled that required say 5
ft.lb torque to compensate, that would mean as far as I can see that the
2.0L a/c is about the same efficiency as the liquid cooleds of the same
vintage. This would be fun to evaluate.
What do you think?
Kim Howe
khowe@omninet.net.au
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