<VV> Vacuum Advance? Re: custom distributor curve?
FrankCB at aol.com
FrankCB at aol.com
Fri Feb 22 14:22:11 EST 2013
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.
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?
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
> weights out there but that is about it. How do I know what kind of
> 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
> 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
> Put the fast set in and try it... then the Medium... Then Mix
> You may fine a "sweet spot"
> But first and foremost.... remove you Vacuum advance...... that is
> economy..for the Dummy...
> Matt Nall
> Charleston, Oregon
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