Re: Distributor recap long read

[Doug Ahern <D170A833@xxxxxxxxxxxxxxxxxxx>]

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On 59 03/23/05, Schuyler Wrobel wrote:
> my family and our excessive amounts of luggage the Poly pulled us
> over the grades and passes that normally gave me a little trouble,
> an annoying slight ping at part throttle, now there's no ping no
> backing down... no one is gunna pass me on the hill.  please read

If your happy with the wagon's performance, thats all that matters
but on a street car, if you can't get your stock ignition to work
with VA (vac. adv.)  then it would appear to me that something is 
a foot.  I went back and read the thread, and it seems like some 
points were skipped.

like, how does an engine benefit from VA? and why do street cars 
have it?  remember that VA primarily exists deliver better economy 
and efficiency during part-throttle cruising conditions.  It does 
not function at WOT, which means you should have no VA (or very 
little) when passing other cars or gettin on the express way.  
Its when you are maintaining cruising speed, or coasting.   If 
you drive around with a vacuum gauge, you'll see when your VA 
is working and when its not working (or supposed to...)

Schuyler, you experienced an "annoying slight ping at part throttle"
right?  sounds like denotation?   If you step down on the throttle,
the pinging with stop because the vacuum disappeared, and will out
vacuum (or with less vacuum) the VA cannister stop advancing 
the ignition, and proper ignition (not pre-ignition/detonation)
will occur earlier (maybe 35deg. instead of 50deg.)...  For a normally 
functioning car, this means #1) you've got too much advance 
(initial adv.+mech. adv.+VA), OR #2) your using a gas that ignites 
too quickly (octane is too low).  If its #2, do what Bob Hope advised 
and "knock out the knocks.." with high octane (more resistant to early 
detonation).   If its #1, and its a stock (more or less) ignition 
system and a stock/mild engine, reduce the initial timing or 
tune (dial) your VA to provide slightly less advance.

sometimes detonation occurs at cruising speed and when you begin to 
take a slight incline, yet you haven't given the engine any additional
throttle.  In this case,  total advance is the same (VA in effect),
but because of the incline, there is more work to do, and the load 
on your engine has increased which will result in increased cylinder 
pressure and increased tendency to detonate.  at this point, you need
less advance, so you step on the throttle and VA backs down...  less
advance plus more gas...  the perfect thing for a wagon with 1000
pounds of people, pets, and luggage going up a hill :-)

any street car, especially heavy ones with highway gears, will benefit
from VA.  its for economy at cruising speeds...   

Remember:

Total adv @ high rpm and WOT = 
	initial timing + mech. adv.

Total adv @ high rpm and part-throttle = 
	initial timing + mech. adv. + vac. adv.

the total amount of advance needed depends on many things (cam profile,
compression ratio, rearend ratio, weight the car, etc).  your car is
somewhat unique in that for most 318 build-ups, yours is a heavy car
(with what I suspect are cruising gears, 3.23:1 or 2.93:1)
I don't think someone (an ignition company, engine builder, or
otherwise) can look up in a some chart and say "this cam in
a 318 needs this much advance"... 

Of course, its your thing, dowatchawannado,, but I suspect
that a well tuned ignition with a fully functioning distributor, 
WITH vacuum advance would give you the best overall performance,
drivability, and economy.

Doug Ahern
Athens, GA

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