Date:         Fri, 9 Feb 2001 19:24:27 -0800
Reply-To:     pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         pensioner <al_knoll@PACBELL.NET>
Subject:      Ullage, Oil Temps etc.
Content-type: text/plain; charset="iso-8859-1"

Hi volks,

From ancient yore on  the BMW AirHead tribal knowledge base.  One of the
doddering old Typ 246 motor experts did a little test.  The motor ran cooler
if it had oil only to the fill mark not to the full mark.  In addition, the
measured HP at the rear wheel was slightly better.  Had to do with two boxer
pistons of 500cc displacement moving air in the crank case.  The more oil,
the more frothing about and so on from the crank motion.   The less oil as
long as within reason, the less wasted effort sloshing it about.  Not my
numbers but worthy of note.  This stuff was written up in Chi Tech an ad hoc
journal of technical knowledge about the venerable boxer twin..

On my 77 RS and the 81 RS I NEVER run oil at the full mark.  The self
correcting 77 will simply dump it out the crankcase breather into the intake
until it has a stable equilibrium regarding oil quantity.. Oddly this is a
shade  over the fill mark.

As long as the intake tube for the oil pump has oil at a reasonable
temperature your motor will do fine.  It doesn't know how much oil is
available as storage it only knows temperature and volume.

Some racing motors run as weak as 5psi at idle as they're set up with larger
clearances by the builder.  No they don't last too long but failure is not
because of low oil pressure.  To quote a famous drag racer, Don Garlits:

Running one of these here AA Fuel motors, we get around 30 to 45 seconds at
full throttle between rebuilds.  Kinda like tryin to keep a half dozen lit
roman candles in a wet paper grocery bag.  You can do it but not for long.

Recall that 30 seconds at WFO was 5 or 6 runs... Usually all that was needed
at a meet to secure his usual spot on the podium.  Connie Kalitta once
mentioned the quote and said he'd gone one better:  We don't count the
seconds.  If it stays together for four runs, we swap it out and rebuild.

Ullage refers to the amount of air displaced by the piston motion.  For a
boxer twin the pistons move in syncronism displacing ~1 liter on each
stroke.

pensioner