Ed Anderson wrote:

 > >   Stated another way - If the pump is driven with  pulleys that result
in a

1:2.17 ratio then it should be turning at prop RPM. So this should be
exactly the same as if it were bolted to a Lyc (assuming that the pump

on a

Lyc is driven at a 1:1 ratio from the crank - I dont know if that is the
case). If a lyc drives at some  ratio other than 1:1 then you need to do
some simple math to figure out what the pulley sizes need to be to get

the

right ratio on your 13B.

  Having said all that, forget the vacuum and go all electric. If you

must

have vacuum it sounds like the smog pump is the way to go.

Mike Wills

Actually Mike, for the LYC 320 and 360s the vacuum pump ratio to engine
speed is 1.3:1.  I used pulleys from 7 1/2 to 5" in diameter trying to find
that magic ratio.  (The 5" pulley was great at low rpm but quickly killed
the pump at high rpm). But, while it worked it just was not satisfactory in
terms of pump life and vacuum performance.  When I had the pulley size that
would produce good vac at low rpm the vac pump would be short lived at the
high rpms.  When the pulley was sized so that it survived at high rpms it
did not produce enough vacuum at low rpms.  At least that was my experience.
I did not readily give up on it and tried to make it work as it was much
lighter that the air pump, however, after going through two pumps in one
year, I decided to go with the smog pump.

Ed

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