Date: Sat, 17 May 1997 14:24:02 -0400
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: kelphoto@mail.bright.net (mark keller)
Subject: Long Life Motors part 2 the nitty gritty
Below, I have provided my laymen's understanding and explanation of the
various issues in part 1 and ways to solve some so that we can obtain long
term benefits. They are a complicated set of inter playing variables at
work here. I covering an appreciation of them sort of and so specific
fixes. Anyway here's my perspective on the issue of improving : my vehicle
and BTW my wallet, bank account, and retirement fund.
Why else should we care? Still need another reason? Engine Life, MPG,
increased Horsepower, lower cooling demands are all areas a vanagon could
use some refinement in.
So, for me, road horsepower is the main statistic that describes what the
vehicle is doing in the real world. Brake horse power, the amount of the
90 or so horsepower that doesn't get eaten by a host of things from the
its journey from the piston to the tire. Things like, friction,
accessories, xsmn's, especially autoboxes, and you name it. Brake hp.
doesn't take into account how much the vehicle weighs, rolling resistant in
the tires, nor the air resistance, nor estimated fuel consumption. BHP
just lets me know how much work the engine could do if it had to. Another
point, Bhp doesn't translate to well with different driving styles, as I
think about it.
More importantly some engine can produce 50 hp very economically, but not
produce anymore than a total of 100 hp. Typically engines that produce two
hundred horsepower, will be gas hogs at producing 50hp.
So to determine what I want in my vehicle road horsepower required tells me
what the whole package needs, to do go down road. Longevity typically is
related to the "strain", ie: how much of the available power in percent is
needed most of the time, in percent. So if I mainly cruise at 60 mph , 95%
of the time on interstate, and my engine has to produce 50 hp to do this,
then my domain is going to be how do I either reduce the required
horsepower, an how do I produce it the most efficiently.
Good choices in Commuter vehicles, I feel are best at maneuverability, in
other words can it changes speeds, either fast or slow, rather quickly. A
Vanagon's Visibility is plus in traffic, but it pretty much is a loser
every where else, on paper. Like climbing a short on-ramp to merge with
high speed traffic. Ouch, lots of ponies needed for that stuff. So your
Loaded camper is not numero uno for big city beltways!
So to determine, reserve power. And if I build a motor, I would like for it
to produce the required road horsepower at the engines most efficient rpm
range. For example.
I considered a couple of alternative engines, the flat six Porsche and
Subaru, which produce the 200 + hp of a real performance class motor.
Problem is they are gas hogs at making the 50 hp you need most of the time.
This is because of the fixed timing of the camshaft to crankshaft, which
allow a combination of high intake air velocity and the intake valve to
cram air into the cylinder at a very specific RPM, say 5500 RPM, the
motor's Max hp RPM. This is the main way to increase hp in motors, air
velocity, and how long can you shoot air into the cylinder via valve
timing. Bigger isn't better here. There are very specific internal
diameters of the intake system, that keep the air velocity at optimum.
Problem is where do I want the optimum. Optimum is for me at or very near
the required road horsepower, fudging of course for hills, wind, and
baggage.
MK
91 Carat.
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