More Comments on Re: <VV> Two Questions

FrankCB at aol.com FrankCB at aol.com
Thu Jun 28 16:04:46 EDT 2007


 
Andy,
    Did you measure the spark timing change before and  after you installed 
the Dale vacuum advance/pressure retard unit?  The  stock turbo Corvair, unlike 
EVERY OTHER Corvair, has FIXED timing all  the way from idle to nearly 4000 
rpm (or until boost is achieved).   The speed of the combustion in the chamber 
varies with the density of the  mix, so, for best efficiency, it is necessary 
to use MORE timing advance with  LIGHT throttle openings which give LOW 
density mixtures and LESS timing advance  with HEAVY throttle openings which give 
HIGHER density mixtures.  When  boost is achieved the density of the mix becomes 
even HIGHER  necessitating further reductions in timing advance which we call 
RETARD  since the resulting timing is LESS than the base timing at idle.
    It is also possible that your carb is so far out of  adjustment that the 
enrichment of the mixture occurs at the relatively high  intake manifold 
vacuums that are present with normal highway driving with  advanced timing.
    In order to ascertain true mpg values, you have to  measure for many 
"fillups".  I'd say at least for 1000 miles of driving and  preferably more, since 
each time you fill up, you most likely have a different  amount of gas in the 
"full" tank.
    Frank "timing is (almost) everything"  Burkhard  
          
 
In a message dated 6/27/2007 8:51:20 PM Eastern Daylight Time,  
slowboat at mindspring.com writes:

Have  never experienced this "bog" that so many of you have described. I have
the  Dale P/R unit on the 180 and it accelerates from idle just fine.

One  thing, though, I never did get ANY improvement in gas mileage when  I
installed the P/R pot.

Anyone have any idea why?
Thanks
Andy  Clark







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