Date:         Fri, 3 Mar 95 11:22:06 PST
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Al Knoll <alf@hpptc38.rose.hp.com>
Subject:      Distributors etc.

A few notes from ye days of olde.  Your 009's advance curve can be measured
by any good distributor shop.  If you have an idea of the cam parameters and
can tune the Solex having a shop customize the curve is pretty simple.

The basics:

1.  A pair of springs with a particular spring constant retain a pair of
weights.  Centrifugal force based on speed of rotation pulls the weights
against the springs moving the advance plate around the shaft so the point
cam moves wrt the shaft.  If you place yourself on the shaft thereby ignoring
the engine rotation and push the weights out the advance plate will rotate in
a direction opposite to the actual rotation of the shaft presenting the points
follower a little sooner in the rotation.  This causes the points to open 
earlier by some amount.  This amount measured in degreees of offset is the 
"advance" for that particular balance between the springs and the weights..

2.  Any speed shop worth it's shingle can "tune" your distributor by selecting
springs, custom shaped weights, and advance plate pivots to give you what 
you need to fully enjoy your intake system/cam timing.  

3.  The trick is to provide a stochiometric approximation of 15:1 fuel to air
with an advance that matches the gas dynamics of your intake/combustion chamber/
exhaust system.  If it sounds too easy, it isn't.  Throw in flame front
progression dictated by plug placement and firing efficiency and you have an
interesting statistical solution space in a fair number of variables some of
which you can't easily control.

Elegant a priori solutions are pretty tough to do so the basics of cut and try
tuning from an experienced knowledge base is the most effective solution path.

A good speed shop has the "stuff" to do this for you.  You'll do it once, 
document the hell out of the result so you can do it again, and have a custom
fit ignition for your motor that can be adjusted as things change.

I remember 104 RON, 11.5:1, Carter AFBs, 45DCOE9s, and awesomely powerful 
motors of the past.  Yep, fuel was $0.35/gal and JFK was a senator.  My personal
ride had 4cyl, 4cams, solex downdrafts and plastic windows and I should have 
never bargained that old carrera for trip through academia.  

Now back to my regularly scheduled programming.

alf@hpptc44.rose.hp.com