According to some trendy types, you can never be too rich or too thin. If you’re a torque wrench-wielding big-block enthusiast, add that you can never have too much ignition power. Today’s hot rodder can choose from three basic levels of sophistication for the ignition system:
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1. Traditional distributor and a spark box
2. Crank trigger and a spark box (the distributor merely acts as a rotary spark switch to feed the juice to each plug wire)
3. Fully computerized using either a distributor with a cam synch sensor or a crank trigger, which still requires a cam synch sensor and distributor to function as a rotary switch
Ninety percent of you are perfectly served with the first option, especially if the car is driven on the street, and the crank trigger option number-2 is good for the 9 percent of you racing your big-block at the dragstrip with engine speeds up to 8,500 rpm. The computerized system gets the call when you go Unlimited drag racing in classes like NHRA Competition Eliminator or Pro Stock, or if you have an aftermarket EFI induction system.
Distributors, Coils and Spark Plug Wires
Stock big-blocks came with cast-iron Delco-Remy distributors until 1969 (Corvettes until 1974); then the switch was made to aluminum-bodied point distributors. In 1974, the HEI was introduced and was standard issue until computercontrolled EFI systems came out in 1987. The HEI is a unitized distributor with magnetic reluctors to trigger its internal control module and an ignition coil built into the large-diameter cap. It was and still is a very good design for most high-performance big-blocks, offering more precise timing control than point distributors, and the larger cap lessened the possibility of cross-firing with the higher voltage that it generates. The coilin- cap was changed from the old oil-filled cylindrical design to a more effective transformer design, and most modern aftermarket coils have followed suit.
Although General Motors called it a “high energy” ignition system, it did not supply adequate spark intensity to turn more than 5,500 or 6,000 rpm, which is fine for most people, but not for any selfrespecting performance enthusiast. Simply removing the stock ignition module and using one of today’s modern ignition boxes, like those offered by Accel, Mallory, or MSD (the popular 6-AL), provides all the ignition performance you need until you get into the race-only systems. The downside to this approach is that most old HEI distributors are quite likely mechanically worn out, exhibiting excessive shaft-to-bearing wear, corroded and sticking advance weights, and leaky or sticky vacuum advance canisters.
If your HEI is worn out, you can buy a new version from GMPP or the aftermarket, or switch to an aftermarket distributor with a smaller cap and remote coil. The small-cap distributors are much easier to service when the big factory HEI distributor cap barely clears the firewall, as is the case with most muscle cars.
Spark plug wires are the critical connection from your distributor cap to the plugs, and all modern wires have some amount of electrical resistance to lessen radio frequency (RF) interference with the other electronic circuits in your car. Even racing plug wires need this resistance due to the wide-spread use of sophisticated ignition systems, automatic shifters, data acquisition computers, etc. While stock resistor wires use simple non-metallic conductors to cut down on RF, high-performance wire sets are much more sophisticated. Many use wire wound around a central core to cut down RF interference. “Fat” wires (8.5 and 9 mm are popular) with heat-resistant silicon jackets and other advanced features are a good investment for your highperformance engine.
The ignition box senses the very low current signal from your distributor or crank trigger and amplifies the voltage considerably, sending a powerful current to the coil where it is amplified again to produce 50,000-plus volts to the spark plugs. While the old point distributors sent a 12-volt signal to the coil, some modern ignition boxes send as much as 460 to 580 volts to the coil. Obviously, the coil must be matched to the ignition controller. Many ignition controllers offer options such as rev limiting to prevent engine damage from a missed shift or broken drivetrain components, start retard to ease the load on your starter, and even digital ignition curves to replace the mechanical weights and springs in your distributor.
The early cast-iron and all-aluminum heads used 3/4-inch-reach gasketed spark plugs with a 13/16-inch hex, while most 1970-and-later iron heads switched to the smaller taper seat “peanut” plugs with a 5/8-inch hex. Many gearheads use anti-seize compound on the plugs in aluminum heads.
Some spark plug experts say that anti-seize should not be used because it inhibits the plug’s ability to conduct heat away from the combustion chamber, but I’ve been using it for years and my motors didn’t know they weren’t supposed to like it. Whatever you use, make sure that the plug threads are lubricated, especially with aluminum heads. With high-compression domed pistons, it’s important to index the plugs so that the electrode is in the upper half of the chamber when tightened, to avoid contact with the piston. Use a felt-tip marker to indicate the electrode’s position on the porcelain and keep switching the plugs around until all eight have the mark facing away from the piston domes. Moroso offers a plug indexing kit with copper gaskets of various thicknesses to help get all eight plugs pointing in the right direction, but these affect the heat range of the plug and should not be used unless absolutely necessary to get proper indexing. Highcompression ratios and high-RPM operation requires plugs with a colder than stock heat range, and most competition engines should not use extended tip plugs, which are used on stock engines to extend the service life of the plug.
A typical plug gap is .035 inch, though some HEI systems fire with gaps up to .045 inch, producing a hotter spark. Very high compression ratios may require reducing the gap to .025 inch. Defective spark plugs are rare, but it does occur. Checking for high internal resistance with an ohmmeter before you install them is always a good idea.
You should check with the manufacturer for recommendations, but spark plugs recommended as either stock replacement or by aftermarket cylinder head manufacturers for typical applications. At right is a list of some.
Batteries and Cables
If you relocate the battery to the trunk for better weight distribution, make sure to use larger-than-stock gauge cables to compensate for the extra length, and run a separate ground cable from the battery to the engine block, as well as to the chassis. Heavy-gauge battery cables are available from Meziere Enterprises, Painless Performance, and other sources. Twelve-volt automotive systems are actually designed to work with 14.7 volts supplied by the alternator, so if you are running a drag race car with no alternator, I highly recommend the use of a 16-volt battery like the TurboStart by Axion Power. The 16-volt batteries are compatible with all aftermarket ignition systems and starters, and there are resistors available to drop the current to 12 volts for sensitive electronic devices, such as throttle controllers or the ECU for computer-controlled EFI systems. TurboStart 16-volt batteries with a third 12-volt terminal are also available for the same purpose.
Written by Tom Dufur and Posted with Permission of CarTechBooks