[DeTomaso] vacuum advance on Duraspark II systems

[Will Kooiman]

You also get 2-3 extra mpg with vacuum advance, plus the engine runs cooler.

I tried manifold vacuum for a while.  I couldn't get the engine to choose an
rpm to idle at.  It would hunt all over the place.  Once I switched to
ported, the idle was much smoother.  This was on my 428 Mustang.  The
effects were very noticeable.

Will.

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of ProvaMo.com
Sent: Friday, May 09, 2008 5:48 PM
To: SOBill at aol.com; lee_farrell at sbcglobal.net
Cc: detomaso at realbig.com
Subject: Re: [DeTomaso] vacuum advance on Duraspark II systems

Thanks Bill, your answer was clearer than mine.

And on my car I have a port off one carb metering block.

Seems to work - grin.

Chuck


-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of SOBill at aol.com
Sent: Friday, May 09, 2008 2:50 PM
To: lee_farrell at sbcglobal.net
Cc: detomaso at realbig.com
Subject: Re: [DeTomaso] vacuum advance on Duraspark II systems

Lee,
 
Holley carbs typically have two vacuum ports: one above the  throttle
plates; 
one below the throttle plates ( called "ported"  vacuum).
 
The one below the throttle plates has full manifold vacuum. Full  manifold 
vacuum is max when the throttles are closed and near zero at wide open  
throttle. If you connect this port to the distributor, you will have max
vacuum  
advance at idle and whenever the throttle plates are nearly closed ..... as
in  
cruising.
 
The one above the throttle plates has zero vacuum at idle,  the  vacuum 
increases as the throttle plates begin to open, and  then falls off again at
wider 
throttle openings. If you connect this port to the  distributor, you will
have 
zero vacuum advance at idle (which can make for a  smoother idle), normal 
vacuum advance at part throttle, and zero vacuum advance  at wide open
throttle.
 
Modern cars, when they still had distributors used ported  vacuum.
 
Be aware  that this is a semi-religious subject.
 
SOBill  Taylor
sobill at aol.com
 
 



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