Date: Sat, 28 Jul 2007 13:50:30 EDT
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Re: Power output of actual vans? (long)
Content-Type: text/plain; charset="US-ASCII"
In the archives, I have posted a number of analyses of torque and brake
specific fuel consumption as a function of net gearing to the road for VW and Audi
I4, WBX and Subaru engines. These were based on actual measured output curves
coming down to torque at the tire patch. I attempted to show the impact of
drag (aero and mechanical) as well as mass for the Westfalia and its impact on
residual thrust available for acceleration and hill climbing. I attempted to
show that many of the accepted wisdom forms related to gearing, performance and
fuel economy were system issues that had to take into account the inherent
pumping efficiency of the engine (what usage range was it designed and then tuned
for). The generally accepted geriatric nonsense that regearing for lower
cruising rpm at higher load factors would deliver better fuel economy seems to
continue nonetheless.
I did not treat the Zetec I4 at the time as it was not then a viable
solution. I am preparing a similar dissertation on the various TDi engines and their
tuning modifications complete with extensive design material from VW and Audi
and results from those US and Euro tuners I respect. I'll post these analyses
within the next month, schedule permitting. My previous postings on the subject
(ignored by most amateur conversion engineers in the group) can be found by
searching the archives under my email address: FrankGRUN@AOL.com.
But as Mark and others have reiterated, its real torque or thrust at the
wheels. Or perhaps slightly differently performance is given by the excess thrust
available from the engine at any given rpm after delivering the work needed to
maintain the vehicle in its present state. The fuel economy for a given
engine class (diesel or gasoline) depends mostly on the neural damage of the driver
but secondarily on the internal resonant flow dynamics of the intake system,
the combustion chamber design, the valve profile dynamics and the exhaust
resonances. The Carnot cycle is alive and well so in all cases a turbocharged
engine can deliver better BSFC for a specific power demand than any NA engine.
Again professional engine design is the key. Anecdotal results such as 35 mpg at
80 mph in a fully loaded Westfalia while achieving 0-60 mph in less than 10
seconds belong in the Twilight zone of supersaturated testosterone generators.
Frank Grunthaner
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