1961-1963 Buick and Olds 215 V8 engines, in both 2 and 4 barrel versions,
always used 'carb vacuum'. > From: cmfloyd@chartertn.net> To:
paul.hunt1@blueyonder.co.uk; mgb_zenkus@yahoo.com; barrie@look.ca> Date: Sun,
19 Oct 2008 17:15:14 -0400> CC: mgb-v8@autox.team.net> Subject: Re: [Mgb-v8]
Carb to dizzy connection> > Some of the British cars may have always used
"carb vacuum", but here in the > States, American Iron used full manifold
vacuum for many, many years. The > ported vacuum advance was a smog bandaid
that was applied in the 70s. These > days the onboard computers handle all
that.> > Most distributors can be set up either way if you know what you are
setting > out to do. Some engines may prefer one over the other. Usually these
is not > much difference either way once set up properly. They will both the
job on > the street by aiding fuel economy.> > I use full manifold vacuum
advance on my '79 B because it has a '63 Buick > 215 in it.> > Carl> > -----
Original Message ----- > From: "Paul Hunt" <paul.hunt1@blueyonder.co.uk>> To:
"Bill Zenkus" <mgb_zenkus@yahoo.com>; "Barrie Robinson" <barrie@look.ca>> Cc:
<mgb-v8@autox.team.net>> Sent: Sunday, October 19, 2008 8:18 AM> Subject: Re:
[Mgb-v8] Carb to dizzy connection> > > > Are you sure you have this right?
Normally the two sources are carb and > > inlet> > manifold. Inlet manifold
vacuum is near maximum at idle, rises slightly > > as> > the throttle starts
to open simply because the engine gets more efficient,> > then gradually tails
away as the throttle is opened further. Carb gives > > zero> > vacuum at idle,
rapidly rising to a maximum as the throttle starts to > > open,> > then is the
same as inlet manifold i.e. gradually reducing to zero as the> > throttle is
opened further. How much vacuum you get *does* depend on > > engine> > speed
to some extent, but as engine speed is controlled by throttle > > opening> >
(except on the overrun) it's the throttle that controls vacuum, and the> >
reducing vacuum with increasing throttle is designed to offset the greater> >
tendency of an engine to pink under wider throttle openings by reducing > >
the> > amount of advance on wider throttle openings.> >> > It's *centrifugal*
advance that increases as engine speed increases, and > > that> > takes
advantage of the fact that as engine revs increase there is a > > *reduced*> >
tendency to pink, all other things being equal, so it can take more > >
advance to> > improve efficiency of combustion and hence performance.> >> >
Which vacuum source is used simply depends on the emissions requirements -> >
inlet manifold vacuum gives lower idle emissions as the engine runs more> >
efficiently with more advance. However it has a downside that it makes > >
the> > engine slightly more difficult to start as some advance is applied even
> > during> > cranking. Carb vacuum is usually preferred, if manifold vacuum
were > > better> > for other than emissions reasons it would have always been
used.> >> > PaulH.> > ----- Original Message -----> >> >> > The passenger side
vacuum port is ""timed" meaning vacuum increases with> > engine speed.> >> >
The drivers side port is the "full" vacuum port meaning the vacuum > >
decreases> > as engine speed increases.> >
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