Mike Sutter wrote:
Steve,
I did have the distributor re-curved when I first put the motor together. I
have the specs written down somewhere in my log down in the garage, but I'm
curious what your advance curve is. I would also like to know the specifics
of your engine, static timing, so I could compare apples and oranges. What
are your thoughts on vacuum advance? Before I started this upgrade I had a
stock Autolite distributor (re-curved) with a steel drive gear to live with
the cam, an Allison CDI box (which is now breaking down @ 5500 RPM) and a
Blaster 2 coil. Stock cap, rotor and plug wires. No vacuum advance. The car
ran great until the spark box started coming apart.
Mike Sutter B382002475
I have included a wider distribution of my thoughts, for those who are
interested. For those who already are familiar with your ignition,
stop here.
Mike,
If you sere just racing, I would guess a strictly mechanical advance would be
useful, but we cruise, go up and down hills, etc. When you are cruising, or
going down a grade, your engine is lightly loaded, and can stand a great deal
more advance, without ping. The carb
ported output, for distributors, does no read manifold vacuum, but reacts
depending on throttle position and load. Normally, a vacuum
distributor on a Ford would not want to have a TOTAL advance of more than 44-48
degrees MAX. This accounts for the static setting, the mechanical advance
maximum limit, and the vacuum advance maximum limit, and would only occur going
down hill with your foot off the throttle. When operating at WOT (wide open
throttle) the manifold vacuum is low, and the ported vacuum is "none", or
atmospheric, which results in no vacuum advance. Under these conditions,
depending upon engine details such as compression ratio, gasoline, "hot spots",
spark plug temperature, you would not want to exceed 27-29 degrees advance.
This is where you would be with a mechanical advance only distributor. This
mechanically determined advance consists of three components.
1) The limit on the particular (replaceable) distributor weight plate guide.
Mine is labeled 10 degrees. But, these are 10 "distributor"
degrees, which are 20 engine degrees (the number we normally discuss). Similar
plate in mechanical only. I have timed the engine static
advance (idle) to be 7-8 degrees BTDC (Before Top Dead Center). This gives a
maximum of 27.5 degrees maximum advance, adding the two. No matter what you do
to your car, on normally available fuel, you wouldn't want to ever push beyond
29.
2) The vacuum advance is controlled on the stock distributor with washer shims.
If you don't have the original mechanism ( and suck on
the rubber hose, if you get air you have a broken diaphragm and need a new unit
- it isn't working). I replaced my 'leaker'
(same unit unavailable to my knowledge) with an Accel replacement cannister.
The vacuum advance is adjustable with an allen wrench in the hose tube entry
(supplied). This is a little tricky, as you need a vacuum gauge and pump to
pull the diaphragm, and a timing light to see the effect, until you get the stop
distance (max advance) you want. I used 10 distributor degrees (20 engine
degrees) at 20" mercury vacuum. This is stock 260. The easier method is, if
you believe your stock unit is factory correct, is to measure the amount of pull
arm max movement, in the old unit, until it hits it's limit. Then, just turn
the allen screw to match.
3) Another consideration is the rate of advance of the mechanical
weight/springs. Stock is not very good. I've set mine to allow full
mechanical advance at about 2200 rpm. It starts to move at rpm's above idle, and
goes in a straight line to the limit of 20 degrees + static 7 deg.at 2000 rpm,
then stays there. Many theories here about dual curves, faster rates, etc. If
you were just racing, or pulling a trailer, you might want something different..
This is controlled by the springs you put on your weights (and the weights
themselves), but these rarely need changing. spring kits are readily available,
and come with general instructions. If you could find a "Distributor Machine",
which they haven't built in 30 years, all this stuff is easy because you can do
all of it on the 'bench'. If you have a good hotrod source, see if he's got
one, and talk about your uses. I had to be really careful here, because most of
these guys are into circle track or drag, and are only interested in full
throttle performance. I've had some really bad advice from "Pro's", even about
carburetor, for this reason. Got to get YOUR needs taken care of. BTW: If you
are using any kind of electronic points, they had better have the electronic
conversion
units, or these old machines won;t read right. I'd hold off on changing from
points until after the distributor work, if you are using a
"machine".
4) Timing lights are available for about $70 that have an adjustment knob, and
maybe a meter, to give you the ability to bring the TDC
mark back to the indicator on the motor, and read off the advance, and the rpm.
Really handy, unless you've got a 'degreed' balancer.
5) I have been using the Pertronix Ignitor points replacement. It is steady as
a rock, never needs 'dwell' or 'gap' adjust, installs quickly
(file the electric connector "eyes" sides a little, if your distributor has the
narrow hole, to get them through). This works well with a stock
distributor, but if you use a "hot" one (70,000 volt), make sure you get the
kind that say "for point type distributors", and you
probably have to use the resistor that comes with the coil. A volt meter and
their instructions will let you know.
6) I have only heard that the Mallory MSD-6AL is a good unit for Tigers (and
other cars). You'll have to find somewhere to put it, and
you may have to buy their "tach" adapter, or use a capacitor as Gary Winblad
has suggested. You might ask him about the MSD unit. E
mail: gary_winblad@juno.com (Gary A Winblad) .
Stand back and wait for all the dissenting opinions. They may have some
'value-added", or correct some 'mis-statements' I have
accidentally made.
--
Steve Laifman < One first kiss, >
B9472289 < one first love, and >
< one first win, is all >
< you get in this life. >
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