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

[burkhard at rochester.rr.com]

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