>  I think the cheapest, lightest, and most reliable way to
       create vacuum
       >  for your steam gauges is with an exhaust bung.
       >
       >  The exhaust bung would enter the exhaust pipe at a small
       angle, say 20
       >  degrees, pointed towards the exit, and extend into the exhaust gas
       >  stream about 1/3 of pipe diameter.  This creates a venturi,
       and LOTS
       >  of vacuum.
       <snip>
       >  IMPORTANT NOTE: you will have to regulate the vacuum (with a
       >  regulator), but it will work very well.  (Almost TOO well.)
       >
       >  So:
       >  lightweight - a few ounces of bung material and tubing
       >  reliable - as long as the engine is running (same as vacuum
       pumps)
       >  durable - no moving parts
       >  cheap - tens of dollars with no annual maintenance
       >
       >  How's THAT for Experimental Aviation?
       >
       >  - Vince Orton

       >
       >    Wow that might be a great idea pulling on the pistons. Super
       cheap
       >    turbo compound.   How do they keep the oil vapor in there? For
       >    drag racing I guess they don't care.
       <snip>
       >    For use as a vacuum pump to drive the instruments it sounds
       great.
       >    These are also called "air ejectors" if you want to look
       them up on
       >    Google.  A simple venturi might generate the -5 psi required
       for vac
       >    instruments without all the back pressure.
       >
       >    Paul Lamar ...No rotor no motor.
       <snip>
       >  Paul,
       >  Modern street motorcycles have used this technique for some
       years now.
       >  They run at very high RPM's of course. Kawasaki was the first
       to use this
       >  system to my knowledge. (In the late 80's)They have had a
       exhaust reed
       >  valve system with a small orifice to the crankcase to pull vacuum.
       <snip>
       >  If your instrument will tolerate oil you're OK. Otherwise be sure
       >  the crankcase is NOT connected to the vacuum generator.
       >  Bill Jepson
       >
       >
       >  I can see how it would reduce the windage HP loss of pushing
       air out
       >  of the cylinder with the piston going down and up into the
       cylinder
       >  with the piston going up. The rotary does not have that problem
       >  fortunately so I don't see a need for vacuum in the crankcase.
       >
       >  Paul Lamar ...No rotor no motor.

       *************************************************************************


       ACRE -

       Wow.  This thread has gone far afield.

       Forget crankcases.  Forget oil vapor.  Forget H.P. increases.

       Use the exhaust bung to SIMPLY create vacuum, regulate it, and
       use it to
       drive your steam gages.  That's it.

       IMPORTANT NOTE: This will create TOO MUCH VACUUM.  Something on the
       order of 15 psi, if memory serves.  You WILL need to regulate it.

       The point was that with this solution, you will not need to
       worry about
       mechanical problems, shearing shafts, pump maintenance, pump
       weight, and
       all the other things that go along with a mechanical solution.

       Yes, smog pumps are cheap, but an exhaust bung in cheaper, more
       reliable, more durable, less maintenance, and ... LIGHTER.

       - Vince Orton

       Vince what do you mean by an "exhaust bung"? Do you have a dwg?

       Paul Lamar ...No rotor no motor.


   How much vacuum is generated during engine idle?  Consider a long
   'slam dunk' power off descent through the clouds from 12k to sea level.


   Matt-


Answering my own query, I suppose one could arrange for an exhaust
throttle for such situations.  The throttle would route exhaust through
a venturi (restriction).  Diesels use them to generate braking force..


Matt-



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