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Electronic Ignition Systems for 1955-1974 Corvettes

Light My Fire

John Pfanstiehl Feb 9, 2017 0 Comment(s)
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Corvettes have had electronic ignition systems for over 40 years, starting with the powerful, dependable Delco HEI (high energy ignition) system in 1975 models. Prior to that, nearly all Corvettes, and pretty much every other motorized vehicle since the Model A, had the same simple ignition system. The spark that ignited the air/fuel mixture came from a set of points, a condenser and a coil.

This simple ignition system was used for many decades because it was inexpensive and dependable. OK, for the younger readers, we should mention there was something called a “tune-up,” which was required periodically. It consisted of replacing the points, condenser and spark plugs. For high-mileage drivers and performance enthusiasts this ignition system maintenance was often needed more than once a year.

Condensers and coils can last many years; points were the main problem. They had to open and close each time a cylinder fired. At a 3,000-rpm cruising speed that’s 12,000 times a minute for a V-8, adding up to around 12 million times per 1,000 miles driven. When the points were closed, current flows through the point’s contacts and the coil. When the points were open, the current stops, the magnetic field in the coil collapses and the high-voltage spark to the plugs is generated.

There can be some minor sparking at the point’s contacts, too. Small bits of metal can transfer from one contact to the other, and eventually the point contact surface appears rough or even burnt. A secondary problem area is the point’s rubbing block that is constantly being pushed by the cam lobes in the distributor. As this wears, the timing is retarded.

Electronic ignition systems eliminate the points and the associated wear issues. They produce a stronger spark enabling spark plugs to continue firing for longer periods and they maintain a strong spark in the higher rpm ranges. This is an important advantage for engines going north of 6,000 rpm.

There are a few trade-offs of electronic ignition systems that should be noted. The first is cost. Although the least expensive PerTronix system costs less than $100, a full distributor and system can run over $800.

1955 1974 Corvette V8 Electronic Ignition 2/30

Dependability must be discussed, too. Some early electronic ignition systems had issues. The first Corvette transistor ignition systems left some unhappy drivers stranded on the road. By comparison, today’s well-known aftermarket electronic ignition systems have a better reputation for reliability. But nothing’s perfect and if an electronic ignition module fails in upper state Maine or most of Nevada, the local parts store is unlikely to have a replacement. Points for a Delco distributor, on the other hand, are easy to find.

Another electronic ignition system issue to be aware of is their minimum operational voltage. When the battery voltage is low with a points system, the spark won’t be as strong, but it will still spark. However, some electronic ignitions will provide no spark at all when a certain minimum voltage is reached.

I learned this firsthand at the Scottsdale Barrett-Jackson auction when a friend asked for help with his restomod C2, which developed a starting problem. The battery was low from many restarts but still cranked the engine. The perplexing thing was that its new electronic ignition system sometimes provided spark and sometimes it didn’t. Generally, electronic items don’t recover when they fail. But this started every time it was jumped. The fastest solution was to install a fully charged battery and then minimize restarts.

The low-voltage issue with electronic ignitions requires that many of these systems bypass the factory wiring. Previous to HEI, GM vehicles—and many other brands—used a resistor, and later a resistance wire, to lower the voltage at the coil when running. This added resistance was a component of a system designed to help cars start easier. Starter motors draw so much current that they reduce the battery output voltage to 10 volts or lower. The solution was to use a low-voltage coil that would produce a strong spark when cranking. After the car starts, battery voltage increases to 14 volts or higher, and the resistance was used to reduce the voltage at the coil.

The resistor on 1955-’67 Corvettes is a discrete component located on the firewall where it’s easily accessible. This makes it easy to bypass the resistor for the installation of an electronic ignition system. Just connect the electronic ignition to the ignition switch side of the resistor. Disconnect the wire from the other side of the resistor and leave it in place.

The resistance wire employed on 1968-’74 Corvettes runs inside the engine compartment wiring harness. One option is to locate the resistance wire at the large bulkhead connector and use standard copper wire to bypass it. An easier option for some is to install a relay. Note that a relay is required if the new system draws more current than the factory wiring can handle. The relay is energized by a small current supplied by the factory resistor wire. Only two wires need to be added: a ground wire and a power wire from the horn relay junction stud. This is a simple engine compartment task.

Choosing the best electronic ignition system is not as simple as there are many options. A primary purpose of this article is to make clear the pros and cons of the various systems. Reading the product sales literature is not often enough. For example, it took five phone calls, three faxes and two emails to nail down the specific differences between models of just one manufacturer. Let’s start with the least invasive systems.

Systems for Stock Distributors

The lowest cost systems also require the fewest changes to a stock Corvette. The factory tach drive distributor, plug wires, and coil can be retained. Plus, the stock ignition shielding can still be used. The PerTronix Ignitor has been available for over 40 years and costs under $100. Its single electronic module replaces the points and fits entirely inside the distributor. For over a dozen years, the Ignitor has been available in two models. The original model employs a magnetic ring that attached under the rotor to trigger the module. Note that the magnetic ring model requires removal of the distributor if the distributor shaft has more vertical clearance (play) than that model tolerates.

The newer, Lobe Sensor model is triggered by the lobes on the distributor cam and does not require removal of the distributor during installation. Note that this model has the suffix “LS” on the end of its part number. That’s useful to know because some suppliers still have old ad copy describing a magnet ring for the LS model. Both Ignitor models have two wires coming out of the distributor.

The PerTronix Ignitor II introduced a safety feature that prevents damage to its module if the key is left in the On position while the engine is not running. Plus, it increases the dwell time at higher rpm for a better spark and can be used with many low-resistance performance coils. The Ignitor II uses the magnetic ring and therefore requires the removal of the distributor during installation if its shaft has too much vertical clearance.

The PerTronix Ignitor III has all the advantages of the Ignitor II but adds multispark and a user-adjustable rev limiter. Both III and II models draw more current than the stock ignition and therefore installing a relay is recommended. The Ignitor III uses the lobe sensor and also works with very low resistance coils. All the above modules can use stock plug wires and the spark gap can be increased up to 0.005 inch over factory specifications.

Another system that fits inside the factory distributor is the Breakerless SE Ignition Kit. It costs less than $200 and uses a two-piece shutter that attaches under the rotor to trigger its module. It has only one wire coming out from the distributor. An advantage of any of the electronic modules that simply replace the points inside the distributor is that should the electronics fail; the points and condenser can be reinstalled roadside.

New Electronic Distributors

The next level up in changing to electronic ignition is replacement of the entire distributor. HEI distributors are self-contained with all the electronics and the coil. Factory HEI distributors are inexpensive (used) and very reliable but don’t have the tach drive for 1962-’75 Corvettes. One option is to have your mechanical tach converted to an electronic tach.

Aftermarket tach drive HEI distributors, made offshore, are also available for the surprisingly low price of around $150. If the HEI distributor has the standard HEI cap, the male ends of the original non-HEI plug wires won’t connect to the male terminals of the HEI cap. Also, the taller tach drive HEI distributors will preclude the use of the original distributor shielding. A “small cap” tach drive HEI distributor, offered online, provides more clearance but requires an external coil.

If your Corvette is missing the original tach drive distributor, new ones are available with PerTronix electronics inside. These use the stock cap and therefore permit the use of original spark plug wires and distributor shielding. Also note that aftermarket distributors might not work with some high-rise, early fuel injection or aftermarket intake manifolds.

High-End Performance Systems

The priciest electronic ignitions are comprised of an electronic tach drive distributor, an ignition box and a performance coil. This is not the choice for Corvette owners who want to keep their engine compartment looking stock. It is designed for high-performance applications and can include features like multispark and a rev limiter. Plus, its aftermarket ignition box and performance coil add some underhood bling to a restomod.

The electronic ignition systems described above are popular and widely available through Corvette parts suppliers and performance parts suppliers. Corvette Central, for example, offers all three Ignitor models, HEI tach drive distributors, PerTronix tach drive distributors and performance coils. Looking for more electronic ignition systems options than these is, well, pointless.

Differences Between PerTronix Ignitor Models

Sorting the differences in aftermarket electronic ignition systems is not an easy task. A customer seldom learns the specific differences needed to choose between various models by reading product descriptions in catalogs or on websites. To help with that choice, the following is a detailed comparison of the PerTronix models for Vette readers.

Ignitor

The Ignitor generally can be powered by factory ignition resistance wires (no rewiring).

The Ignitor can be used with OEM coils if they measure between 1.5-4.2 DC ohms.

The Ignitor module may be damaged if the ignition switch is left in the On position when engine is not running.

The Ignitor can be used to trigger most multispark CD ignition boxes.

The Ignitor has a Lobe Sensor model that doesn’t require distributor removal, but this Lobe Sensor model cannot be installed into dual-point distributors.

The original “magnet ring” model is still available but can require distributor removal if shims need to be added above the drive gear. Dual-point distributors require the magnet ring model.

The Lobe Sensor model has an “LS” suffix on the PerTronix part number, but note that some companies selling them still have “uses rotational cobalt magnets” incorrectly listed in the description of LS models.

Ignitor II

The Ignitor II is not damaged if the ignition switch is left in the On position when the engine is not running.

The Ignitor II can use low-resistance performance coils: 0.45-3.0 DC ohms (most coils are OK but not HEI coils or E-core square coils).

The Ignitor II increases dwell at higher rpm to produce a better spark (but this dwell change doesn’t affect timing).

The Ignitor II uses the magnet ring and therefore can require distributor removal if shims need to be added above the drive gear.

The Ignitor II draws more current than a stock ignition system. Bypassing the resistor or resistance wire is generally recommended (can require some rewiring).

Ignitor III

The Ignitor III has all the same features as the Ignitor II model.

The Ignitor III also adds an adjustable rev limiter.

The Ignitor III also adds multispark (two sparks throughout the rpm range).

The Ignitor III uses the Lobe Sensor module and therefore doesn’t require distributor removal.

The Ignitor III requires the use of low-resistance coils (0.32-1.5 DC ohms).

The Ignitor III draws more current than the stock ignition system so the resistor or resistance wire should be bypassed (requires some rewiring).

The Ignitor III cannot be used with multispark CD ignition boxes.

The Ignitor III modules have an 8-degree start-retard that helps hard-to-start and high-compression engines.

All PerTronix Models

Stock (suppression) plug wires can be used with all Ignitor models. Solid-core plug wires cannot be used because they may interfere with Ignitor modules or other electronics.

Voltage at the coil during operation should be above 8 volts. For optimum performance, 12 volts should be applied to all Ignitor modules. This is more critical with the Ignitor II and Ignitor III models.

After initial installation, the timing must be checked and adjusted.

The early version of the Ignitor required the ignition to be turned on for several seconds to “charge” the module before starting. All later models can start instantly.

Except for the 8-degree start-retard of the Ignitor III, PerTronix ignitions do not change timing at any rpm range.

A 30-month warranty covers all models.

Well, there you have it. An easy way to have modern performance in a vintage Corvette distributor; it truly is having the best of both worlds.

Distributor Cap 3/30

01. To make way for the installation of the Ignitor module, the distributor cap and rotor are removed for access to the points and condenser.

Screw Holder Screwdriver 4/30

02. After the three screws are broken loose, a screw-holder screwdriver helps keep them from falling into the distributor or engine compartment.

Condenser Bracket 5/30

03. When the points, condenser and condenser bracket are removed, place them and the three screws into a Ziploc bag. They don’t take up much room, so keep them in the car in case the electronics ever fail.

Corvette V8 Electronic Ignition Jpg 6/30

04. The degradation of the point’s contact surface is a primary reason for switching to an electronic ignition. In just 1,000 miles of driving they can open over 10 million times. The metal transfer can be seen on the stationary contact.

Battery Voltage 7/30

05. PerTronix recommends measuring the voltage at the positive side of the coil to see how much the resistance wire (or resistor) reduces the battery voltage. The negative side of the coil is shorted to ground to simulate the points being closed.

Battery Voltage Measured 8/30

06. The coil’s primary resistance should also be measured to determine if it can be used with the electronic ignition system. Disconnect the wire from either terminal and measure the resistance between the two terminals. At 2 ohms, this coil is similar to a stock coil and can be used with the Ignitor.

Lobe Sensor Ignitor Model 9/30

07. The Lobe Sensor Ignitor model does not use the magnetic ring of the original Ignitor. Therefore, the distributor does not need to be removed for this model as is sometimes necessary for the magnetic ring model.

Ignitor Module 10/30

08. The Ignitor module covers the area where the condenser was mounted and is attached with two supplied screws.

Ignition Grommet 11/30

09. The hardest part of the install is making the supplied grommet fit properly into the distributor hole. The grommet is an off-the-shelf part and does not fit tightly on the two Ignitor wires. A little silicone or other glue can be applied to seal the gap and help hold the wires.

Module Wires Igntiion 12/30

10. Make certain the module’s wires are routed away from the rotor and that they don’t rub on the distributor plate. Remember, the vacuum advance moves the plate counterclockwise.

1955 1974 Corvette V8 Electronic Ignition Conversion 13/30

11. The Ignitor’s red wire connects to the positive coil terminal along with the resistance wire. The Ignitor’s black wire is the only wire connected to the negative terminal.

Corvette V8 Electronic Ignition Conversion 14/30

12. The coil is getting 11.7 volts through the ignition resistance wire at idle. This voltage is high enough that a relay or resistance wire bypass is not needed. FYI, this inexpensive meter from Harbor Freight gave almost identical DC voltage and ohm readings as a more expensive gauge.

Harmonic Balancer 15/30

13. The timing groove in the harmonic balancer was highlighted with a magic marker for easy viewing. To bring the timing groove in sight, the car was placed in Fourth gear and bumped. In case the timing plate is illegible, the deep “V” and hole are at 0 degrees. Every stamped line going upward is another two degrees advanced. This black mark is located at 10 degrees advanced.

Elctronic Ignition System 16/30

14. Timing the engine is necessary after installing any electronic ignition system. The timing was close enough after installation of the Ignitor that it started right up. This single lead Flaming River timing light from Corvette Central helps prevent cables from lying on the exhaust manifold or getting caught in the fan belts.

Corvette V8 Electronic Ignition Conversion 17/30

15. All the stock radio shielding fits over the Ignitor ignition system. With these electronic systems, the engine compartment can retain its factory look.

Corvette Distributor 18/30

16. The distributor did not have to be removed for installation of the Ignitor LS model. However, if removing the distributor for replacement or maintenance is desired, it helps to use tape to mark where the rotor is pointing to enable it to be reinstalled in the same position.

Corvette Rotor 19/30

17. As the distributor is lifted up, the rotor turns a little over 30 degrees counterclockwise. Note or mark where the rotor is pointing; this is where it should be placed when reinstalling the distributor.

Corvette Carburetor 20/30

18. After the distributor is removed, it’s wise to cover the hole so that nothing falls in. Cover the carburetor, too. A little screw falling in there has ruined many a person’s day.

Stock Distributor 21/30

19. This distributor has 0.055-inch clearance, which is not uncommon for stock distributors and creates no problem for points ignition systems. However, this vertical play in the shaft can be a problem for the magnet ring systems. To add more shims or to replace the shaft, tap the roll pin out through the gear. Note the alignment of the circular indentation on the gear to the rotor and make sure the gear goes back on with the same alignment.

Tech Gear Bushing 22/30

20. Even if the distributor is not removed, it’s wise to remove the tach gear bushing for inspection and lubrication every few years. Both the distributor shaft gear and the small gear will last for many miles if maintained.

Tech Gear Bushing 23/30

21. It’s important to closely inspect the inside diameter of the tach gear bushing. If any wear is visible, replace it. The gears strip when a worn bushing allows increased clearance between the gears.

Corvette Oil Pump Shaft 24/30

22. If the distributor doesn’t slide fully down into the manifold, don’t worry. It’s common for the oil pump shaft to rotate a little when the distributor is removed. Use a long flat blade screwdriver to turn it a smidge in one direction or the other.

Hei Distributor Caps 25/30

23. HEI distributor caps are much larger in diameter than stock caps and have their coil mounted on top. Plus, the male terminals on these caps require HEI-style spark plug wires. Smaller cap HEI distributors are available but require an external coil.

Hei Tach Drive Distributor 26/30

24. This HEI tach drive distributor just barely fits into this 1973 small-block. The original air cleaner can be retained but the radio shielding won’t fit over this large cap.

Tech Drive Distributor 27/30

25. The most expensive option is installing a tach drive electronic distributor, and ignition box and a performance coil. This system can cost over $800, but delivers a hot spark into the high rpm range and adds some bling.

Corvette Spark Plug 28/30

26. Installing well designed spark plug wire looms is essential regardless of whether the wires are being run underneath or over the top, as is common with headers. Without proper looms, the plug wires will eventually sag or fall onto the exhaust and burn.

Factory Heat Shields 29/30

27. These factory heat shields have been removed from many Corvettes. However, they are essential to protect the spark plug wires and their wire ends from the intense heat of the exhaust manifold.

Measure Spring Tension 30/30

28. For owners wanting to stick with points, it’s very easy to measure the spring tension. Over the past several years, I’ve bought Delco points that had defective or weak springs. Perhaps they were counterfeit; I never had this problem when installing hundreds of Delco points sets back in the day. If your engine runs out of steam and starts backfiring at 4,500 rpm and higher, measure the force required to open the points.

Sources

PerTronix Performance Products
San Dimas, CA 91773
909-599-5955
pertronix.com
Corvette Central
Sawyer, MI 49125
800-345-4122
www.corvettecentral.com

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