<VV> Vacuum Advance? Re: custom distributor curve?

[kenpepke at juno.com]

Has anyone yet realized the term 'vacuum advance' is a misnomer?  In fact, that thing with the vacuum line that is hanging on the side of the distributor momentarily RETARDS the timing when the throttle is opened to give the extra fuel from the accelerator pump time to get to the cylinders.  This prevents a momentary very lean condition which would surly result in a heavy, and undesireable, spark knock.  

Ken P
Wyandotte, MI
65 Monza 110hp 4 speed 2 door
Worry looks around; Sorry looks back, Faith looks up.

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On Feb 22, 2013, at 11:22 AM, FrankCB at aol.com wrote:

> Removing the vacuum advance (and plugging the line  connecting it to the 
> carb) might make sense to a strictly performance-oriented  Corvair, but IMHO 
> is the wrong choice for any car driven in normal street  traffic.  And it's 
> not simply a case of fuel consumption.  Vacuum  advance also greatly improves 
> part throttle response such as accelerating from a  traffic light or even 
> when changing lanes in traffic.  
>    Consider the completely stock turbo Corvair that  comes with NO vacuum 
> advance and only has pressure ignition  RETARD that works at rpms ABOVE 4000 
> (for the 1965 and 66  models).  Driving these cars in traffic means using a 
> CONSTANT FIXED  ignition timing (24 degrees BTDC) until you get above 4000 
> rpm AND  achieve some boost.  When you compare the STREET driving 
> performance  of the turbo Corvairs against the 140 engined cars it's no wonder that so 
> many more 140s were sold than the turbo Corvairs!
>    Adding vacuum advance to a turbo Corvair not only  produces 
> significantly better fuel mileage (I got over 20% improvement) but also  improves the 
> throttle RESPONSE of the engine when driving in  traffic.
>    You can read more about this in my Turbocharging  Chapter 33 in the 
> Corvair BASICS manual available from CORSA.
>    Frank Burkhard
>    Boonton, NJ    
> 
> 
> In a message dated 2/21/2013 6:34:09 P.M. Eastern Standard Time,  
> 62vair at gmail.com writes:
> 
> OK Matt,  now I'm the dummy. I understand about the three spring kits, but I
> need an  explanation of the benefits of removing the vacuum advance.  I
> don't  drive my street car enough to worry about gas mileage, but would like
> good  steady performance from the engine.
> 
> I also understand the weights and  springs swing in and out at different
> rpm's adjusting the advance, hence  finding the sweet spot, but how does the
> vacuum advance mess with that? It  works off of manifold pressure, but I
> haven't sent any time thinking about  the interrelationship between the
> mechanical and vacuum advances in the  cars. I would think the vacuum
> advance would continue to advanc the enine  beyond the capability of the
> mechanical advance. Am I wrong?
> 
> So,  what benefit is there in removing the advance alltogether?
> 
> Mark  Durham
> 
> On Wed, Feb 20, 2013 at 5:21 PM, Matt Nall  <patiomatt at aol.com> wrote:
> 
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