Hi Daryl,
I agree with what you're saying, and to some extent I've been there, done
that (well, I never autocrossed at the regional SCCA level). I ran a Toyota
2T-C using an optical sensor in the distributor - I forget the brand. The
redline was imposed by the pushrod rigidity, and that made the rev limiter
an absolute necessity for those times when I got over-hasty with the
throttle on the track. In 1991 I built a crank triggered wasted-spark
ignition for a friend with a Toyota 4A-G twincam, using fixed dwell and
timing set using a crank-pulley mounted disc that interrupted two optical
sensors. It got him an extra 20 hp on the dyno, just because the stock
distributor is driven off the exhaust cam and at high RPM the timing scatter
is bad enough that it costs serious horsepower. Crank-triggered
distributorless ignition, whether it's waste-spark or coil-on-plug, is THE
way to go for ultimate timing. Like you say, it's not cheap and installation
requires a good understanding of what you're doing. If the bolt-on parts are
not available then good fabrication skills are a must. Fortunately Ford
briefly offered the Explorer with a crank triggered ignition; in my pile of
"someday" parts is a cam position sensor/oil pump drive that replaces the
distributor. Right now I'm setting things up to use the TFI distributor,
with a modified Megajolt Lite Jr. module providing vacuum and RPM dependent
advance.
I agree that CDI systems offer limited benefits, but if you know what to
expect from them then you won't be disappointed with their operation. A nice
feature of the MSD box that I took advantage of, was that it accepts the
reluctor sensor from my Ford EEC distributor, and that lets me operate
without the Motorcraft ignition module. It also provides a clean tach
signal. CDI systems in general are within the capability of the average
backyard hobbyist to install, which is what gives them their big appeal, but
of course they won't fix underlying distributor problems or issues with the
carburetor jetting.
The newer generation points replacement (such as the XR-3000 or the
Pertronix Ignitor II) have one big advantage over the earlier gen stuff: The
automatic dwell circuit shuts off the coil current if it detects that the
engine isn't turning over. This saves the coil and the module from
overheating if you leave the ignition turned on with the engine stopped (for
whatever reason).
All the various "high voltage" claims can be pretty much disregarded for the
street. Ignition spark voltage is a function of the cylinder pressure and
the plug gap. The conventional automotive plug is designed to ignite at the
lowest possible voltage, by having sharp corners on the electrodes. If you
run high compression, or supercharging, then the required voltage goes up;
similarly, if you run a very wide plug gap, then the required voltage goes
up, and if it's high enough then you could potentially cause insulation
breakdown in the coil or in the plug wires before the plug can fire. In that
case, you need to invest in a better coil, probably a distributor cap
specifically designed for the purpose, and a better set of plug wires.
As with anything: Read all the documentation you can on a product before
buying it. Get an understanding of what it will and won't do for you. Make
sure that the underlying mechanical parts are in good functional condition
first - you don't need the last 10 horsepower that a zoomy ignition system
could get you, if you're missing the first 30 because the distributor shaft
is bent.
Theo
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