Ignition advance, was Re: alternative engines, WARPED

[Todd....!!]

Venturi vac is not considered to be the same as ported vacuum,

The venturi's are up in the top of the carb, the ports are way down in
the manifold... two TOTALLY different vac readings...

The vac advance vacuum should be from a vac source which is located
between the throttle blades and the intake valves... known as port vac..

CL, your theory is pretty correct, for a naturally aspirated car with no
form of ram air...

However, with a turbo/supercharged/SERIOUS ram air car(at high speed)
manifold vac can read anywhere from neg to pos...depending on the
conditions...

On the turbo/supercharged cars, if the timing isn't controlled by
computer, then the vac must be pulled from a different source...

Sincerely,

Todd....!!

-----
CLsnyder wrote:
> 
> ----- Original Message -----
> From: Aaron Willis <darkmonahue at awwwsome.com>
> To: <diy_efi at efi332.eng.ohio-state.edu>
> Sent: Wednesday, May 19, 1999 2:06 AM
> Subject: Ignition advance, was Re: alternative engines, WARPED
> 
> > At 12:47 PM 5/18/99 -0400, you wrote:
> > >Just use manifold vacuum.  Carb vacuum is ported so there is no vacuum at
> > >idle.  This can help or hurt the idle quality.  Try it and see.
> > >
> > >Gary Derian <gderian at oh.verio.com>
> > >
> >
> >
> > You sure about that?  I have always understood that a vac advance can
> > reads ported vacuum in order to affect a curve that begins as the throttle
> > is opened and increases as more throttle is applied, up to the point at
> > which all vacuum (manifold and therefore ported as well) fades under heavy
> > throttle openings, at which point the advance will decline again and the
> > engine will see only mechanical advance.  This is apparently to provide
> > extra advance for economy at part throttle.  Anybody who can further
> > illustrate this concept, please do because if I am wrong here I'm going to
> > have some serious rethinking to do!
> >
> >
> > Aaron Willis
> > ICQ #27386985
> > AOL IM: hemiyota
> > http://surf.to/garage-te51 Garage TE51 International
> 
> Ported vacuum is also known as Venturi Vacuum. The only time it is zero is
> with the engine shut off or at idle. As soon as you have airflow you have
> advance - although it is reduced at WOT. Some implementations just take the
> vacuum from above the throttle plate and below the venturi. These will lose
> most of the vacuum at WOT.
> 
> Switching from port to manifold on a slant six helped the midrange power and
> driveability considerably, but sure hurt economy.
> 
> By the way, Aaron - that AOL IM brings back memories. Back when the Golden
> Triangle Drag Park, or Toronto International Dragway was in operation, Jack
> Frame Toyota campaigned a little 1972? Corolla 1600 in showroom stock called
> the Hemiyota. Balanced and blueprinted with open exhaust it kicked major
> butt. I worked for Fleetline Toyota (Waterloo) at the time.