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Holley History: Holley Develops the Copper Core Spark Plug

By: Jim Hill | 01/02/2020 < Back to Motor Life Home
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Soon after Holley was acquired by Colt Industries in 1968, Holley management began an aggressive campaign to target opportunities in the growing automotive performance and racing aftermarket.


One such product was spark plugs, made exclusively for Holley by Hitachi Ltd. Rather than put their name on a product similar to what was already available, Holley worked with Hitachi to bring to the market a spark plug that was vastly different. Engineers at both companies spent considerable time developing the new plugs for popular U.S. domestic engine makes, paying particular attention to matching critical heat ranges to ensure buyers could easily choose the correct Holley spark plug. The development of a cross-reference chart allowed performance engine builders to choose Holley spark plugs with the same heat range that they were currently using from other manufacturers.

In the early 1970s, the spark plug market was dominated by three brands: Champion, Autolite and ACDelco. They had one component in common: The center electrode was made from cast-iron alloy. But the new Holley spark plugs featured a copper alloy center electrode. The copper core provided an edge over the cast-iron core, as copper offers an efficient conduction path with reduced current loss, translating to more spark energy delivered to the cylinder. This was crucial as new, more powerful ignition systems were being introduced to the performance and racing markets. Higher current output meant hotter ignition performance, better efficiency and, most important, increased torque, throttle response and horsepower.


This improvement was especially attractive in high-horsepower racing engines with high static compression ratios, typically in the 13.0:1-and-up range. Greater current and hotter spark energy are required, especially at high rpm. The extreme cylinder pressure commonly seen in these engines literally tries to “blow out” the early spark kernel as it occurs. These new copper-core spark plugs provided greater current conductivity, produced more spark energy, improved combustion and resulted in increased engine power.


The Holley spark plugs offered other features not found in other brands, including an injection-molded ceramic insulator with the highest alumina content of any plugs sold, a gas space 20 percent larger to reduce fouling and misfire, a nickel alloy electrode to resist burning and pitting and advanced sealing cement at key points for better durability and to prevent gas leakage.

To launch the new spark plugs in 1972, Holley went directly to its Holley Winners Circle members, a select group of accomplished drag racers running in sanctioned NHRA, AHRA and IHRA regional and national events. They consisted of a cross-section of vehicle makes that included Chevy, Ford, Dodge, Plymouth and AMC. Holley backed its new spark plugs with hefty cash contingency awards: $25,000 for NHRA, $14,000 for IHRA and $12,000 for AHRA.


One of the earliest nationally known racers to use Holley spark plugs was Billy “The Kid” Stepp. He fielded a Pro Stock 426 Hemi Dodge Demon and Hemi 1968 Barracuda, The Barracuda ran in both Super Stock/A and sometimes B/Gas in Modified Eliminator. Billy’s engine builder, tuner and crew chief was Paul Frost, a widely regarded Midwest engine and tuning ace. Billy’s drivers included Don Carlton, Ken Dondero, Stuart McDade and Bobby Yowell. 


Billy’s Pro Stock cars were major players in both NHRA and IHRA regional and national events, and they logged many match race dates across the nation. His cars also set numerous track records and NHRA Pro Stock records, all while running and endorsing Holley spark plugs. 

Other racers who recorded wins with the new Holley spark plugs included Sam Auxier, Steve Bagwell, Paul Blevins, Carroll Caudle, Tony Feil, Val Hedworth, Bill Hielscher, Carl Holbrook, Bo Laws, Maskin & Kanners, Dan Parker, Tom Tiganelli, Ken Van Cleve, Dave Wren, Bobby Yowell and many others in Eliminator categories, from Stock up to Competition Eliminator and Pro Stock.


The growing success of the Holley spark plug product line came to an end when Holley Performance Products was sold by parent firm Coltec Industries in 1998. The decision was made not to renew the marketing agreement with Hitachi and the spark plug line was discontinued. But up until that time, professional and sportsman drag racers across the nation found race-winning performance in the form of Holley spark plugs. And thanks to their groundbreaking innovation, the copper-core spark plug became the standard for all manufacturers – until the advent of platinum spark plugs in the 1990s.

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