<VV> Spark Delay Valve - yay or nay?

[Sethracer at aol.com]

I'll  take that as a nay ;)   The SDV is history.  Thanks!

-  Steve

While the correct name maybe as you stated, the fact is  that these are a 
vacuum advance delay. The delay is for the activation of the  vac adv for 
emissions control and come in various delays stated in seconds (of  time) and decimal 
fractions.

These were not used on  Crvairs.
Regards,
Bob Helt



Not so fast folks. Bob is correct, sort of. They were never factory  
installed on Corvairs. But their function can allow them to be used as a  Band-aid for 
some Corvairs. As I recall, the vacuum delay valve was used to slow  down the 
return of the vacuum advance to zero, not to slow down the application  of 
advance. Mostly AMC cars used it but some GM also. The quick snap back of  
vacuum, when the throttle was closed, caused some emission problems, as well as  
idle stumble. The valve was used to slow the return when the throttle was  
closed, sort of a dampener. On the Corvair - primarily on the 110HP Automatics,  
often prone to acceleration ping, several folks have turned the valve around and 
 used it to slow the application of the advance under acceleration. It dos 
not  affect the amount of Vacuum advance, just the rate at which it comes on. No 
 restriction exists in the stock system, as you come off idle, the full 
amount of  vacuum is instantly applied to the advance diaphram and, quite quickly y
ou get a  shot of vacuum advance. It drops back as the vacuum drops off, as 
the  throttle is opened further, but using this valve slows the application. I 
don't  think it has much effect in normal driving at part throttle, where 
vacuum  advance is a load indicator, since the delay is short. I'll bet Jim B. has 
some  info on this. - Seth  



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