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Pair of mystery single overhead-camshaft big-block Chevrolet heads turn up at auction

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Photos courtesy Steve Linne.

Racer Jack Conely might have been best known for the “maxi-mouse” small-block Chevrolet engines punched out to big-block proportions, but squirreled away among his stash of racing parts were two prototype overhead-camshaft Chevrolet big-block heads that bring up more questions than they answer.

Described in the auction of Conely’s collection merely as a pair of aluminum hemi heads, the two semi-machined pieces carry few identifying marks — only a casting date of January 11, 1966, and what appears to be a part number — but look almost identical to the heads in a rare GM photo of an experimental chain-driven single overhead-camshaft Mark IV big-block engine.

Image via GM Media.

According to Steve Linne, who bought the heads at the auction (for $2,550, as reported in the auction’s results), they’re “semi-machined,” with completed combustion chambers, valve guides on the intakes only, spark plug holes drilled and tapped, and the cylinder-to-block mounting bolt hole registers complete; but still missing valve guides on the exhaust sides and featuring rough-cast camshaft journals and blank bosses for the camshaft cover.

No camshafts, followers, valves, or associated parts came with the heads or appeared to have been included in the auction. Nor did any history come with the heads. Both are also right-hand heads.

Known as the Brighton Bandit “because he was always stealing the show wherever he went,” Conely raced mostly on oval tracks in and around Michigan, Indiana, and Ohio, and even made at least one attempt at the Indy 500, failing to qualify in a car powered by an engine he built himself. When his racing career ended in 1974, following an injury he sustained in a crash at Jackson Motor Speedway, he devoted his efforts to building race engines.

Not long after, he developed the maxi-mouse small-block, which he offered in sizes up to 482 cubic inches,  according to an article in the August 1977 issue of Hot Rod Magazine. According to that same article, Conely “has had a close working relationship with Chevrolet Motor Division research and development programs since 1957… Jack has run these engines using every type of experimental head Chevrolet has cast since 1963…”

Conely didn’t limit himself to small-blocks, either, as can be seen from the rows upon rows of big-block crankshafts and both steel and aluminum big-block blocks and heads offered at the auction, which took place the last weekend of September. According to a website dedicated to Conely, he built engines for NASCAR, USAC, Indy, IMSA, and ARCA racers. In 1987, the Michigan Motor Sports Hall of Fame inducted him into their ranks.

Safe to say that Conely, who died last year, obtained the pair of heads through his contacts with Chevrolet but never got around to completing the machining of the heads, let alone building a complete running engine from them. Whether Conely obtained the heads for a semi-official testing program or as surplus after Chevrolet discontinued the SOHC Mark IV program (or how many pairs of heads he received) is unknown.

Linne believes he can build a running engine around the heads, however. He has already reached out to GM’s Heritage Center for more information (and, hopefully, engineering drawings of the missing pieces), and has inquired with the Conely family to see if the left-hand mates to the heads are still hanging around.

“With 3D printing now available maybe, just maybe, it may not take a king’s ransom to at least determine direction,” Linne said. He also noted that he’s eager to compare the heads to a pair of aluminum 427 Ford SOHC heads in his collection.

Aside from the heads, the Conely auction also included three race cars: the 1964 Edmunds Indy car in which Conely attempted to qualify for the Indy 500 in 1966, which sold for $130,000; a 1970 Lola T190 Formula 5000 car, which sold for $27,500; and a 1968 AAR Gurney Eagle Mk 5 Formula 5000 car, which sold for $60,000.