Date:         Mon, 15 Jul 2002 23:22:24 -0400
Reply-To:     Christopher Berchin <ctb1@PEOPLEPC.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Christopher Berchin <ctb1@PEOPLEPC.COM>
Subject:      tiico's, subies and diesels oh my...
Content-Type: text/plain; charset="iso-8859-1"

I have gotten my spreadsheet to a point where it is share-able.  Please note
the following disclaimer:

What it does:
* Proves beyond a shadow of a doubt that I am truly a geek
* Uses dyno data to calculate thrust and acceleration, along with
approximating powertrain losses and drag forces
* Calculates drag using the standard Drag Equation, using the VW-quoted Cd
of 0.44.  This is for a non-Westy, pre-1986 model.
* Takes into account the weight of the vehicle
* Takes into account the tire size
* Takes into account all gear ratios
* Allows one to compare various engines to get an idea how much engine
performance can change
* Provide hours (?) of fun for noodling around the various combos
* Show you the effects of higher-RPM engines.  For example, the long legs of
the 6500-rpm engines allows you to downshift to 3rd gear to climb that tough
hill at any speed below 80mph.  With a WBX, you're stuck until you fall
below 65 mph.  And so on.


What it does NOT do:
* Help my case to peers that I am sane
* Estimate RPM-dependent losses, such as increasing load in the alternator
as RPM climbs.  I considered those lumped into the generic "powertrain
losses" percentage that you see in the sheet.
* Incorporate rolling resistance of different tires
* Account for static loaded radius of the tire instead of theoretical
radius.  NOTE:  I have made a version where you can input a known revs/mile
of a tire and it back-solves for SLR based on that and the tire size, so
there is a way to do it.  In fact, I better check that I haven't
inadvertently left that in one of the sheets.
* Give exact, cannot-be-disputed numbers
* Provide accuracy commensurate with NASA launching a Space Shuttle
* Account for automatic transmission slip
* Account for tire slip at speed
* Account for tire growth at speed
* Account for tire pressure changes
* Account for aero effects of spinning wheels, open windows, fat tires, and
so on
* Hold the key to cold fusion
* Provide true data for the 1.9 WBX.  I don't have a torque curve for that
engine (and sadly, that's my engine!), so I took the max HP and torque
values and RPM quoted by VW and iterated until I got what looked like a
believable curve compared to the 2.1.  Those two engines aren't all that
different, so this seemed good enough for my purposes
* Use an exact frontal area in the drag coefficient.  I modeled the bus as a
perfect box in front view, with 12 inches subtracted off the vehicle height
to approximate ground clearance.  Not scientific, and I know this.  Quick
and dirty to see the effects of drag on top end, as it increases with the
square of velocity.  That makes a difference to loons like me who use their
Vanagon for 75+ speeds almost exclusively.


Misc bits
* This concept was written by a friend of mine to compare theoretical
accelerations of his 220-lb butt on his motorcycle and my 145-lb butt on
mine.  We also used it to see how well the gear ratios were chosen on the
bikes - i.e., did they provide nice intersecting curves, or did acceleration
fall of hugely in between gears?  I heavily modified his original
spreadsheet and concept into the monster you see here.  Hence the fields
"Ride weight" and "Bike weight" in the sheets.
* I have included a 2.5 Oettinger TDI engine in the comparison.  All dyno
data is from Oettinger's site, and I do NOT know if this engine can be
slapped into a Vanagon.  Their illustrated use is in a Eurovan.  However,
there are Vanagon TDI's out there, so I thought it would be fun (for
me...never really planned on making this mass-consumption) to see how much
poop a TDI has.
* HP is calculated from torque; the basis of the entire calculation is
torque data from a dyno.
* All data is from the manufacturer or tuner and is crankshaft power EXCEPT
for the 1.9 WBX - see above
* If anyone has dyno data from a chassis dyno, BRING IT ON!  That data will
reflect true powertrain losses, rather than using the semi-standard amount
of 15%.  Syncro folks:  your losses are definitely higher than 2wd.  I have
dynoed cars in the past, but not my bus.
* Torque must be entered in lb-ft.  Anything else will blow the numbers out
of whack, but the trends will be the same.
* I never intended for this to really be used by a ton of people, so it
isn't at a level of polish that would make it ready for sale at Best Buy.
I'm sure there are some inconsistencies in labeling, etc.
* If the thrust (after drag losses) is less than zero, then you can see that
the vehicle will be aero-limited in top speed.  If the thrust remains
positive to redline, then that means the vehicle could pull that speed given
enough time to accelerate.  THAT'S THE THEORY - however, the numbers are not
exact, due to the things outlined in "What it does NOT do" above
* "Rho" is the Greek letter used to denote density, in case you are
wondering when you see the sheet.


The file is located at http://groups.yahoo.com/group/vanagon/files/, titled
"Vanagon Engine Comparos.xls."  I am "ctbtyper," as that is my Yahoo email
address.  (It loses something without the caps - CTBTypeR - but I digress.)

Suggestions, corrections, better dyno data, more dyno data/graphs for other
engines (Tiico would be cool), etc., are all welcome.  While I am no
stranger to flames, I don't as yet own Nomex underwear, so I'd really rather
you phrase flames as suggestions for improvement rather than questioning my
ancestry, ridiculing my barely-adequate brain, or pointing out what an idiot
I am.  Those things have all been done plenty, so if you're gonna flame,
make it original!  Think like the bar scene in the movie "Roxanne."  : )  I
will accept the names of good counselors, however...

Clive:  I think I answered your questions with the above disclaimer.  If
not, certainly do go ahead and drop me another line!

Last thing:  it's meant to be fun and interesting, not Einsteinian in
significance.  Don't stake your life on a bar bet claiming that your TDI can
accelerate at over 1g, no matter what the graph says.

Cheers, enjoy, ciao baby.

Chris