(followup) Re: Alternatives Re: <VV> Rebulding Retard?

[Frank DuVal]

And...

They also limited the spark advance vacuum to only work when the 
transmission was in high gear. This was before overdrive.
My 1970 Buick Estate Wagon with a three speed manual tranny had the 
switch mounted on the side of the transmission where it would only be 
pushed with the third gear fork lever. I took that off early in my 
ownership! The Turbohydromatics had the switch internal.

Frank DuVal

burkhard at rochester.rr.com wrote:

>Andy, at al - 
>
>Pondering it a bit, here's what you may have been thinking of:  After 
>emission regs started taking effect, one thing that the OEMs did do to 
>control NOx (at part load) were vacuum switches that would 
>limit/eliminate vacuum advance to the distributor when the engine (and 
>hence the catalyst) was still cold.  The engine would run without 
>vacuum advance (i.e. like a dog) until it got warm enough and then the 
>thermal switch would enable it.  Under retarded spark, engine out NOx 
>is reduced because peak combustion pressures are reduced (which result 
>in lower temps and *that* reduces NOx). The retarded spark also 
>*increases* the temperature of the exhaust gas which yields some 
>improved oxidation of HC / CO prior the catalyst and (bonus) the hotter 
>exhuast gets the catalyst lit off quicker (which is when teh tailpipe 
>emissions really clean up).
>
>Jim Burkhard
>
>----- Original Message -----
>From: Andy Clark <slowboat at mindspring.com>
>Date: Thursday, February 22, 2007 1:41 pm
>Subject: Re: Alternatives Re: <VV> Rebulding Retard?
>To: burkhard at rochester.rr.com
>Cc: virtualvairs at corvair.org
>
>  
>
>>Thanks, Jim. Interesting stuff.
>>You're probably right about HC and CO being the concerns at idle. 
>>I was
>>going on (failing!) memory as to the reason for ported vacuum.
>>The Cord does not seem to sag off-idle perhaps because all that 
>>happens is
>>that the timing goes back to 24deg BTC as it was before the vac 
>>adv was
>>added. So I probably don't notice the difference. No problem 
>>getting the
>>idle where it should be, though.
>>Thanks again for the education.
>>Andy Clark
>>Camano Island, WA.
>>1966 140/4 Monza Sedan
>>1966 140/4 Yenko Clone
>>1966 180/4 Cord 8/10 #60
>>    
>>
>
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