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Chrysler’s A117 and A148 Hemi Engines for NASCAR

Curtis Redgap wrote:

According to Chrysler (With their terrible record keeping, this is not solid!) the A148 came out of a letter written for Performance Planning in the 426 Hemi engine program on December 2, 1965. The initial parameters within that letter requested variations A864 Hemi, which was the original 426 wedge engine with the Hemi heads developed that aimed at NASCAR racing. While the goals were not set out clearly, it does appear that the engineers were trying to get a faster-running engine (in revolutions per minute) and better breathing to raise the torque.

The letter set down specifications to allow a bigger intake and exhaust valves. While not specifically stated, this program may have been the result of the NASCAR ruling in November 1964 that banned the A864 engine from racing in the 1965 season. Chrysler elected to "sit out" and boycott the NASCAR racing circuits initially in 1965, almost bankrupting Big ol' Bill France. On June 15, 1965, NASCAR rescinded a complete ban on the Hemi, specifically stating that it sought "to eliminate the high cost/low volume special engines from competition." It was, of course, aimed at Ford and Chrysler for the SOHC 427 and 426 A864.

By then, Chrysler had decided to make the 426 Hemi available as a regular production item beginning with model year 1966. This grew from another Planning Letter dated January 6, 1965, about a month after the A148 letter.

The NASCAR decision to allow the Hemi back in restricted its displacement to 405 cubic inches. This announcement came on June 15, 1965, some 5 1/2 months before either of the internal planning letters were released to the engine development programs for the A102 Street Hemi or the A148 "big valve" Hemi.

It didn't take Chrysler engineers all that long to get the 1965 A117 engine built. Chrysler returned to NASCAR with a 404 ci Hemi on July 25, 1965. This engine had a shorter 3.558 inch stroke as opposed to the 3.75 inch 426. It meant a new crank as well. To offset the loss of power, two keys areas were quickly studied: intake manifolding and camshaft timing. Even with the shortened season, Richard Petty, the star of Chrysler, won four events with the 404 ci A117 engine.

Chrysler did not state how many A148 engines it built nor when the program stopped. It mentions that the intake valve size was increased to 2.44 inches, and the exhaust valve was 2.08 inches in this engine. It used longer valve springs to allow higher lift. Both cast iron and aluminum heads were built for this engine. According to the chief engineer on this project, the cost to make it as reliable as the other engines was too high.

Stewart Pomeroy wrote:

This engine was developed to be an insurance policy in case the Ford Boss 429 was what it was reported to be, which it was not. The rocker gear was to be stable up to 9500 to 10,000 rpm; the engine had 464 cubic inches and was tested at other bore / stroke combos and tested as a pro stock head for the early to mid 1970s, but it was not right for Pro Stock as it was a NASCAR design.

It was in essence a 1965-1966 426 race Hemi prototype based on the shorter stroke of the A117 but with a larger bore (4.363 in) and larger valves. Both aluminum alloy and iron cylinder heads were tested with, along with a gear-driven cam and a flat crankshaft.

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