Better Dirt Cheap Electronic Ignition
The Chrysler ignition module is cheap and easy but it is ancient technology. The dwell control is crude and it relies on a ballast resistor to limit current. It is lower maintenance than a set of points but the performance isn't any better. To get more power out of an ignition system you need a coil with a higher inductance and you need to pull more amps through it. Increasing the primary current requires better dwell control to prevent burning out the coil.
Ford created the TFI (Thick Film Ignition)
for use on fuel injected engines. There are two types of TFI systems; TFI-IV and
TFI-CCD. TFI-IV has a dwell control built into the ignition module. Most TFI-IV modules
were gray. A TFI-CCD relies on the computer for dwell timing. All TFI-CCD modules
were black. Both TFIs were available in closed and open bowl configurations. Early TFIs
were mounted to a hole in the side of the distributor housing, these were called open
bowl. They had trouble with the modules blowing out so they started mounting them on a
heat sink away from the distributor, these were closed bowl systems. Pictured is an open
bowl TFI-IV module mounted to a heat sink. The closed bowl modules look identical except
they don't have the three quick disconnects coming out of the top. Most guys don't use the
TFI because it relies on the computer for ignition timing, there is no mechanical or
vacuum advance. I designed a stand alone digital ignition
control which plugs right into a TFI distributor and allows full control of the ignition
curve. Although, you don't need a computer to use a TFI-IV.
I bought an open bowl TFI-IV distributor at a swap meet for $10. It came complete with a module, plug wires, and a brass terminal cap. I also found a TFI coil for $6. The TFI was the perfect setup for my digital ignition. When trouble shooting my ignition I bypassed the computer and set the base timing to 36°, remember with no computer the advance doesn't change. Surprisingly it ran great with the advance locked out. When I was at the drag strip I ran it both with and without the computer advance and it made no difference. I would recommend anyone building a budget drag car to just slap in a TFI-IV distributor and coil. The distributor is easy to hook up, pin 4 is wired to the positive coil lead and pin 5 is wired to the negative coil lead. The positive coil lead is also wired to get power when the ignition switch is on. Not all cars will work well with the timing locked out. My car is only 3,000 pounds, has a 4-speed, 4.11 gears, and I don't lug it. If you have a heavy car, tall gears, or an automatic with stock converter then you will need some sort of advance. The only problem with having the ignition locked out is starting the motor. It won't want to turn over because the burning fuel will try to push the pistons down before the reach the top. The easy solution is to hook up a kill switch that grounds out the negative coil lead. I ran the coil wire to the back of the cigarette lighter. Of coarse, I removed the power wire from the lighter first. When the lighter is pushed in it shorts out the coil and kills the ignition. To start the car I would push in the lighter, then turn the motor over. When it was spinning I'd pull out the lighter and it would fire right up.
If you need some sort of advance, or don't want to mess with a kill switch, the TFI module can also be hooked to a breaker point distributor. The breaker points put out a nice digital signal like the Hall sensor in the TFI distributor. Since the module handles all the current burnt points will be a thing of the past. The points will also go years between adjustments since the dwell doesn't matter. Normally, the open bowl TFI module uses the distributor housing as a heat sink. I modified a heat sink from an Athlon processor to take the place of the distributor housing (pictured above). I mounted the module under the dash to keep the engine bay looking stock. You could also use a closed bowl TFI-IV module. If you get one from a junk yard it will have a heat sink on it. They are both wired the same. Pins 1 and 4 go to the positive coil lead (which gets power when the ignition switch is on) and pin 5 goes to the negative coil lead. Wire pin 2 to the breaker points. The module should be grounded through the mounting surface but a wire from pin 6 to ground will assure a good connection.
Can I hook a TFI to a Duraspark (magnetic pickup) distributor? No, the TFI module has a "digital" input so it won't recognize the "analog" signal from the magnetic pickup. However you can use a GM 4-pin HEI module. The HEI and TFI are basically the same thing but the HEI has the proper input for a magnetic pickup distributor. You can buy a 4-pin HEI module at any auto parts store. If your parts guy doesn't know what that is then tell him you need an ignition module for a '78 Camaro with a 350. The one pictured is a Car Quest #21040 and cost me $17.77. As you can see it has 4 pins labeled W, G, B, and C. G is a 3/16" male quick disconnect the rest are 1/4". The mounting surface must act as a heat sink to prevent the module from burning up. The cooler you keep the module the longer it will last. Securely mount it to a flat metal surface or bolt it to a big heat sink. There are two pins on the back of the module that you need to break off so it will sit flat. The module comes with some heat sink compound, smear it evenly over the back before bolting it down. Pins W and G go to the magnetic pickup. On a Duraspark distributor the purple wire runs to pin G and the orange wire goes to pin W. Run the black wire to one of the mounting screws on the module, this gives the module a good ground connection. The module must be grounded to work properly. You can plug into the Duraspark distributor connector with standard 3/16" female quick disconnects. Pin B on the module is run to the positive coil lead (which gets power when the ignition switch is on) and pin C goes to the negative coil lead.
The TFI upgrade only cost me about $40 and there was a noticeable improvement in performance. The engine runs much smoother and it pulls harder above 5,000 rpm. The TFI is a cheap performer but it isn't perfect. They are notorious for blowing out. Mounting it inside the car with a big heat sink will help but if you are not using points then carry a spare module in the glove box. If you are using points and it blows out then you can just hook the coil straight to the points and keep going.
If you have any questions or comments please e-mail me at firstname.lastname@example.org.