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

[FrankCB at aol.com]

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:

>
>
>
> I'm aware  of the kits of three sets of springs and that there are 
different
>  weights out there but that is about it.  How do I know what kind of 
curve  I
> want, and how do I figure out how to create that curve once I  know?
>
> The Distributor:
> AFAIK stock 140  distributor
>
> The Engine:
> 140 engine
> LeVair 1/8"  over bore stock carbs with other mods (relocate jet etc.)
> Bored .060  over
> 280 Isky Cam
> Increased compression heads (no  step)
> Clarks Ultimate headers exhaust
> 66 4 speed  trans
>
> Use:
> Plenty of street use but trying to make a  good autocross car out of it
> (also road corse, hoping to do the  Olympics this summer).
>
>
> Thanks for any  advice!
>
> Ray R.
>
>  ======================================================================
>
>
>    Ray.....   First talk To   Warren / Michael for their  recommendation!
>  They got  experience!
>
>
>   To properly "re-cure"   you need a Dyno....   to  Chart results...  and
>  then make a decision on a curve,
>
>
>  Then you need  track time to   "  fine tune  it"
>
>
>   Barring that... since you do not have  an assortment of weights and 
Dist.
> Cams...
>
>
> Put  the fast set in and try it... then the Medium...  Then Mix  
springs...
>   You may fine a "sweet  spot"
>
>
>   But first and foremost....   remove you Vacuum advance......  that is 
for
> economy..for the  Dummy...
>
>
> Matt Nall
> Charleston, Oregon
>  http://tinyurl.com/The-Corvair-Patio
>
>  http://tinyurl.com/Matts-Tech-Pages
>
>
>
>
>
>
>
>
>
>
>
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