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. On second thought they lose as much energy as they gain as the
pistons
on the compression up stroke are required to pull up against the
vacuum so to speak.
Same goes for the exhaust up stroke. Looks like a wash. I have heard
about it to reduce windage
on the crank shaft however. Vacuum pumps are sold in the racing
parts catalogs for
that purpose.
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.
They are used in some composite shops for pulling a vacuum on a vac
bag layup.
A simple venturi might generate the -5 psi required for vac
instruments without
all the back pressure.
Paul Lamar ...No rotor no motor.
Make sure it's AFTER the turbo.. :)
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. They
quoted a 1.5 HP increase at redline, not a trivial improvement. Some of the
racers enlarged the orifice, (if a little bit is good....), with mixed
results.
The vacuum that the system pulled was increased, but the vacuum would
unseat the lip seals on all the shafts. The weird whistling caused by some
of the seals passing air even at idle was bizzare! To make it really
work well
you needed to TURN ALL THE LIP SEALS CUP SIDE OUT. This is the opposite
of normal. You could pull 15-20 inches of vacuum on many bikes. This DOES
improve top speed a tiny amount, and drag strip et's a measurable amount.
(.01-.03 seconds if memory serves) The high vac version couldn't be used
on the street unless you carefully watched the oil level. The vapor was
sucked out and the Ninja 900 ('84) that burned no oil in standard trim
would
use about 1 quart in 3-4000 miles. To use this system on an aircraft I
would
worry that you could have a vacuum phenomenon called "backstreaming." The
minor amount of oil vapor left can travel the wrong way, putting oil on the
instruments. 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.
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