Date: Sat, 17 Feb 2001 11:24:55 -0700
Reply-To: Mark Keller <tyler@ISLANDNET.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <tyler@ISLANDNET.COM>
Subject: Road Horsepower vs rolling resistance
Content-Type: text/plain; charset=us-ascii
Derek,
Your topic is very close to a future project of mine-- road horsepower.
So I'll share my thoughts that may be of value but are as of yet
untested.
You've probably read of the road horsepower statistics in vaarous car
magazine
reviews. I recall the parameter of 60 mph, level ground, and sea level
pressure type of conditions. Given that, a Honda Accord or any other 2
liter sized car, required 10 horsepower to maintain a 60 mph
cruise. The exact figures aren't important at this point.
What is important is that the Vanagon requires nearly 60-70 hp to
maintain a 70 mph cruise. Those are ballpark estimates based on the dyno
report
at Volkscafe, i.e. 4000 rpm total wheel horsepower available, 75 hp and
12
inches of vacuum, 80 % power, from my van at 4000 rpm; yields 60 hp. my
future project is to quantify the road horsepower.
My observation is that your increase in cruise speed, necessary in
my opinion, will bring a higher required road horsepower but largely
through increased aerodynamic drag. I do know one drag coefficient for
a early vanagon was .46. The total drag plate area varies from Carat to
Westy, but a guess is 30 sq. ft. The Honda would be like, 15 sq. ft.
Both
are guesses of width x height of vehicle cross-section.
I feel that vehicle height, Carat the lowest, and a Westy Syncro with
the
tall tires the highest, also significantly affects the road horsepower.
Ground effect reduction of aerodynamic drag is enhanced by lowering the
vehicle and thus reducing the amount of airflow beneath the vehicle,
which is aerodynamically full of drag inducing surface variations. I
measured my van height before loading it with 1800 lb.. of cargo, which
lowered the Van by 2 inches. My gas mileage remained unchanged at 21
mpg on the
2400 mile trip. I believe the reduction in ground clearance, reduced
undercarriage
drag, enough to offset the required increase in road horsepower to move
the 1800 lb...
In my opinion, one way for you to offset the horsepower issue is to
by cleaning up the undercarriage of the van thus, improving
aerodynamics.
For a start in thinking, I saw a 4 x 4 mud racer use the 12" x 12" thin
steel
sheets that the dirt bike racers paint their numbers on. Looking at his
trucks undercarriage, while it was on a lift, the plates were duct taped
from the front end all the way to the back wherever he could, much like
flooring tiles. The effect was to keep mud from accumulating in any
undercarriage cavity
during his run. Ours would be to reduce the total area exposed to the
aerodynamic slipstream. Anyone who has tried to drive the vanagon into a
modest 20 mph head wind will attest to the way is saps the engine's
available
power reserve. Upping the top cruise speed is really doing the same
thing.
Although the vanagon is a different animal than a 4 x 4 mud racer, any
effort to reduce aerodynamic drag
in the undercarriage will make a better 75 mph cruising machine.
Sincerely,
Mark Keller
91 Carat
Cowichan Bay, BC
I'd like to dialogue some on this pmail, if you'd like. I'll post this
to the list as I have some other people pass their insight.
