Del Johnson Wrote:

A while ago I threw out the idea of using the exhaust as a source for vacuum
and said that I found one web
search reference that indicated that the Subaru folks where trying it.  Then
last week Perry Casson passed us
information about Phillip Johnson's web site discussion of exhaust tuning
( <http://www.geocities.com/plmjohnson/exhaust.htm>).  That site showed the
installation of a 1/2" tube inserted into the collector for use in creating
a vacuum.  I tried to contact Phillip Johnson but have not received a
response.  Sooo.. I went to the Cozy builders site and searched their
archieve '(http://www.maddyhome.com/cozysrch/search using the search words
vacuum exhaust') and found several discussions threads on using exhaust as a
vacuum source.  Here is one that gives real numbers from a completed and
flying aircraft:

Update on using engine exhaust as source:

Bruce Frank has since installed this sys in his vehicle. He can achieve
9" hg, but has it regulated to 5". Now has it running his two gyros
mounted in his vehicle. As I recall, he gets 3" at 1200 rpm. This makes
in entirely feasible for my application.
His best results using 3/8 x .065 wall ss tubing. Bend at 90 deg insert
into exhaust. Outlet is flared.
System components, inlet filter (std), vacuum regulator (I like $20
version myself), and anti-backfire valve. Saves you 3 lbs (pump) and
$300+. $2k savings if you consider elect gyro.
Since this is a new system, some risk involved. I could see someone
making tube too long and risking fatigue of ss. Or perhaps choosing to
mod exhaust in way that increases fatigue of exhaust. But using std
industry practice of drilling hole in exhaust, welding a "half steel pipe
coupler" in place should be low risk. Millions of vehicles have exhaust
heat measured that way, no failures.
This is definitely the direction I'll take. I'll do a little
experimentation on it, but not much.

Also there is a reference to a Diesel alternator that has an integrated
vacuum pump:

A couple of EAA'ers here in SA has suggested using an alternator from a
turbo charged diesel pick-up since it has a vaccum pump to operate the
brakes.

I own a Isuzu Pick-Up and after scrutenizing teh altenator it turns out
that it turns in the oppposite direction.  It can be corrected by
swinging the pump body thru 90 degrees wich would let it run in the
reverse direction.

Altenators charge in any direction of rotation.

from rec.aviation homebuilt:

http://store.summitracing.com/partdetail.asp?part=9253&view=257#largerimage

Sold as a kit or separately.

Scott V.

and:

tested one on a 4 into one exhaust system back in the late 70's. Was very

powerful.

Jim

and:

Can you describe it?

At the point where the 4 exhaust pipes met the 'collector' necked down to a
venturi like shape. I inserted a small tube at the narrowest point (just like a
carburettor fuel feed outlet). You see there was this hokie theory about
boosting race car engine power by evacuating the crank case so as to increase
differential pressure on the top side of the pistons. Sounded stupid but I
figured I had nothing to lose by trying it. The vacuum was so great that it
kept sucking in my valve cover gaskets. Never lost any oil though since it was
always being sucked back in.

Jim

Charlie England

 
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