Alternatives Re: <VV> Rebulding Retard?

[Andy Clark]

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
----- Original Message ----- 
From: <burkhard at rochester.rr.com>
To: "Andy Clark" <slowboat at mindspring.com>
Cc: <virtualvairs at corvair.org>
Sent: Thursday, February 22, 2007 10:28 AM
Subject: Re: Alternatives Re: <VV> Rebulding Retard?


> I don't have a list, but I'm pretty sure most cars in the 50s - 60s
> took vacuum advance from a ported signal -- that's how it was done on
> the well pre-emission Rochester HV as well as the non-Corvair 1950s
> applications that used the Carter YH (Corvairs using the YH were
> turbos... a special case).  I don't have ready access to information on
> other 1950s-early 60s carbs, but I'm pretty sure ported vacuum was the
> norm on most applications.
>
> As for the ported signal being used only to reduce idle NOx, that
> doesn't make a whole lot of sense. NOx produced at idle is soooooooooo
> small compared to NOx under load!  The NOx reaction is very strongly
> temperature (and hence pressure) related.  Idle (with very low peak
> pressures and temperatures in the combustion chambers) is the LAST
> place you would tinker with anything to reduce NOx.  Worry about HC &
> CO at idle? Yes!  NOx? no!
>
> The reason to use ported vacuum is exactly as my father described -- 
> you need to look at what the two types of vacuum do on tip-ins and
> driveaways.  Plain intake manifold vacuum takes a dive as the throttle
> is opened when you perform a driveaway. If this is used on most
> vehicles, you will get a sag that results from the sharply reducing
> vacuum advance.  Ported vacuum was used instead because it starts
> out "OFF" and then INCREASES as the throttle is opened.  In this
> manner, the base timing can be set a bit higher and then the vacuum
> advance coming in *adds* torque, not pulls it away.  Finally, it's
> common to calibrate idle spark under MBT timing. On modern cars, this
> is down to provide some spark-based torque authority to allow active
> spark control to control the idle speed; on older cars, the somewhat
> retarded spark at idle allows a better misfire resistance and idle
> stability.
>
> So, why does your SS396 (which came AFTER the Corvairs which used
> ported vacuum advance!) not use ported vacuum for its vacuum advance?
> I don't know exactly, but it could be related to the MUCH HIGHER
> power:weight ratio of this vehicle. On a light tip-in the manifold
> vacuum probably doesn't sag nearly as much as with a Vair.  Also, I am
> guessing that that vehicle probably has a pretty wild cam, so it
> doesn't have very much idle vacuum in the first place.  In any event, I
> think vehicles like an SS396 were the exception, rather than the rule.
>
> Jim Burkhard
>
> ----- Original Message -----
> From: Andy Clark <slowboat at mindspring.com>
> Date: Thursday, February 22, 2007 0:30 am
> Subject: Re: Alternatives Re: <VV> Rebulding Retard?
> To: virtualvairs at corvair.org
>
> > Frank, this has not been my experience nor that of many others.
> > Long before the smog regulations were enacted, most, if not all,
> > cars with
> > vacuum advance took the vacuum signal directly from the manifold.
> > With the
> > advent of the early smog regulations, NOX emissions at idle were
> > reduced by
> > reducing the total engine advance at idle, hence ported vacuum
> > advance. I
> > remember my '66 SS396 was ported directly to the manifold and the
> > last thing
> > it had was stumble off-idle.
> > My Cord 180hp engine uses manifold vacuum to a Dale vac/press unit
> > and it
> > too comes off idle smartly and smoothly. The only effect of adding
> > the Dale
> > unit using manifold vacuum was an increase in idle speed, easily
> > adjustedwith the idle speed screw.
> > Andy Clark
> > Camano Island, WA.
> > 1966 140/4 Monza Sedan
> > 1966 140/4 Yenko Clone
> > 1966 180/4 Cord 8/10 #60
> >
> > ----- Original Message ----- 
> > From: <FrankCB at aol.com>
> > To: <louis at suffolknet.org>; <virtualvairs at corvair.org>
> > Sent: Wednesday, February 21, 2007 2:00 PM
> > Subject: Alternatives Re: <VV> Rebulding Retard?
> >
> > > Lou,
> > snip...............................................
> > >     However, this setup now provides manifold vacuum to  the
> > advance at
> > idle
> > > conditions, where you don't really want it since  it tends to cause
> > "bogging"
> > > as the car is accelerated above idle  speed.
> > snip................................
> > >     Regards,
> > >     Frank "likes boost" Burkhard