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I found this interesting article on Allpar regarding the development of a rare DOHC 426 Hemi in 1964:

"A pair of 426 dual-overhead cam Hemis may have been produced in 1964 to counter Ford’s response to the 1964 426 Hemi, the 427 single overhead-cam engine, but when NASCAR ruled against Ford’s engine, there was no need for the overhead-cam Hemi. Recently, famed engine builder Larry Shepard told us that he has the A-925 cylinder head and other related parts, purchased from the late Dan Napp.

An article by Tom Shaw in Mopar Muscle said the DOHC Hemi project was coded A-925, and that it had an unusued contingency plan of using two cams between the heads, with four pushrod-activated valves on each cylinder (which went back to very early hemispherical-head engines). Development mainly focused on an engine with aluminum heads, dual overhead cams, and, again, four valves per cylinder, with pent-roof chambers. (Chrysler had been working with four valve per cylinder engines for a never-completed Indy run in 1963).

The dual-plane intake manifold had eight runners per side and were made of magnesium, with a single four-barrel carburetor, as required by NASCAR. The cams were driven by a cog belt, with external cog wheels at the front of the heads. Because the cams were directly above the valves, valvetrain mass was low, so the engine could rev to a high-for-the-era 7,000 rpm redline.

Tom Shaw wrote that no DOHC Hemi ran under its own power; they were driven by an electric motor to check the valvegear. Research stopped in 1964 when NASCAR banned the SOHC 427 and Chrysler’s race Hemi. One Chrysler DOHC Hemi reportedly still exists.

Jon Field wrote that there was a third Mopar DOHC Hemi made, which he owns —a 301 cid aluminum-block-and-head engine with twin cams, two cam covers on each head (the plugs are between them), hydraulic tappets, brass valve seats, and four Weber two-barrel carbs (165 cfm each). He wrote that the oil pan holds 10.6 quarts, and that the engine has stainless steel headers, and an aluminum intake; he said it was functional and runs on regular gas. We don’t have verification, or information on whether it’s a Chrysler effort or an aftermarket modification.

Chrysler alumnus and historian (of The Ramchargers) David Rockwell and historian Stewart Pomeroy agreed told Mopar Action that the A925 engine program was a fake, meant to impress Bill France into banning Ford’s SOHC engine. The one engine was run by an electric motor. The story goes that Chrysler racing chief Ronnie Householder learned about the ban from Bill France, and the engine was then destroyed."

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My father worked for Westinghouse for 48 years. He said in the 60's Lincoln was using Lincoln engines to 'dyno test' their automatic transmissions in the R&D department. The engines would run at various speeds, including 5500RPM, and would last only a few weeks. Lincoln asked Westinghouse to provide some electric motors to replace the gas engines, which they did, and the motors were still running into the 1980's when Lincoln discontinued the dyno room.
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