Date: Wed, 17 Oct 2001 13:59:19 EDT
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Re: Torque Curves(more comments and Subaru Results)
Content-Type: text/plain; charset="US-ASCII"
In a message dated 10/17/01 9:08:17 AM, ingalls_mark@HOTMAIL.COM writes:
<< Sorry to be out of the loop ( curve? ) but just what engines and chips are
we looking at here?
>>
Just some clarifying comments. As I said in the original post, the key
description of the operation of any engine is in its torque curve. Over the
years I have accumulated a number of engineering articles about the design,
implementation and performance of the engines developed by the VAG group.
These articles include the torque and horsepower curves, the fuel consumption
curves (also called brake specific fuel consumption because they map out the
fuel used per kilowatt generated in gallons per hour as a function of rpm).
Parenthetical aside: I have been trying to combat the accepted wisdom on this
list that says higher-rpm-per-mile means more-fuel-consumed-per-mile which in
turn suggests less-miles-per-gallon. False, false, false! As you will see
from the fuel consumption maps (really do need some place to post this stuff.
May just have to generate a website.) the engine has the same fuel
consumption per kilowatt generated over a wide rpm range. Its highest
efficiency is often in a narrow band (300 to 500 rpm) but the 5% higher
consumption curve often ranges from 300 to 4500 rpm. So (One more time ... )
the actual fuel economy is a function of how much power you use, not how fast
the engine is spinning. Dropping the final drive ratio from diesel levels to
air cooled levels just changes the number of kilowatts you need to the engine
to output to maintain your speed, give the acceleration you request, etc. The
second point the consumption curves show is that the engine is most fuel
efficient at full load. Reduce the load, burn more fuel. From these maps, it
is clear that operating at about 20% of full load output, you will use about
twice as much fuel per kilowatt generated. So for maximum fuel efficiency,
you would choose a gear ratio that loaded the engine to its maximum output at
any given speed. CVT transmission. But this also minimizes longevity (engine
life is proportional to the square of the load - within its rpm design range)
and, for simple transmissions - 4 spd, 5 spd, etc. - eliminates any
acceleration ability. So, the most fuel efficient vehicle VW could put
together would probably be a high boost pressure TDi engine with about 1.3 L
driving a fully loaded Westfalia Vanagon at 100 kmph at 4000 engine rpm.
Sorry for the rant, and back to the engines/torque curves. The articles also
map out fuel consumption against manifold vacuum (for any given power output,
the maximum fuel efficiency corresponds to the highest manifold vacuum),
power requirements vs. velocity, mass, gearing, tire design and inflation,
cam shaft timing, intake manifold design etc, etc. I have found this
information for a window from the ATZ and MTZ journals (all in German) for
1978 to 1992. After 1992, the University of California libraries dropped the
ATZ, then the MTZ subscriptions. The data I have then covers the Vanagon 2.0L
AC, 1.9L WB, 2.1L WB, 1.6L D and 1.6L TD. I also have the data for the G/J I4
engines including the 1.3L, 1.6L, 1.8L (8V) CIS and 1.8L (8V) Digifant and
1.8L (16V); for the Audi I4 engine 2.0L 3A and for the Audi I5 engines both
gas, turbo, diesel and turbo diesel. But, no data for the TDi engines, the
1.9L D and TD, or the VR6. I'm sure this data exists, but I don't have them.
Finally, I have tried to get the data on the Subaru engines (2.2. 2.5 and 3.3
liters) and have come up with NADA. This includes searches through the
internet, magazine data bases and a wide variety of engineering databases. As
far as I could determine, the Japanese approach is no publication! To probe
this issue, I sent an email to Subaru America and Subaru Japan requesting
this information. After a week, I received a reply saying that as a corporate
policy they do not release torque or horsepower curves on any Subaru engine
product! They did volunteer that the torque maximum numbers were as published
in their sales literature :
2.2l engine - 149 lb. ft @ 4000 rpm
2.5l engine - 166 lb. ft. @ 4000 rpm
3.3l engine - 228 lb. ft. @ 4400 rpm.
I'm not impressed. Adds to my general discomfort about the Subaru engines.
For such data only chassis dyno info is available. This is generally less
reliable (varies with operator and Dyno Brand name) but includes several
additional losses to extrapolate the flywheel value. Certainly can be used
for comparisons.
(Steve and Mark, I'm adding a GIF file version of the curve).
Frank Grunthaner
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