From Student Engineer to Performance Icon

For nearly 40 years, Bob Cahill and Chrysler made beautiful performance music together. Now, at age 92, he’s eagerly awaiting his next technological adventure.

Words: Roger Meiners

Cahill started at Chrysler as a student engineer in June, 1936. He went to the engine development lab in 1938 under Bill Drinkard, working on bearings and connecting rods. Cahill credits Drinkard as the “father” of the original Chrysler HEMI® engine. Drinkard was head of engine development at Chrysler. He believed that the hemispherical combustion chamber V8 was the way to go for the new Chrysler engine, but “He had a hard time convincing Chrysler chief engineer Fred Zeder,” said Cahill.

“John Plattner, an exceptional engineer, directed experimental engine development under Drinkard. Plattner assigned James Farley McLelland (nephew of former president Franklin D. Roosevelt’s political advisor and U.S. Postmaster General Jim Farley) to test various cylinder head configurations against the venerable Chrysler inline flathead six. McLelland tested an Alfa Romeo inline six with a double overhead camshaft (DOHC) hemispherical head, a Riley 2.5 liter pushrod hemispherical engine, and a Rolls-Royce F-head engine.

The tests confirmed that the hemispherical heads on the Alfa and the Riley were better than the others in airflow and volumetric efficiency. Chrysler followed up this testing by building two different HEMI-head sixes, one a DOHC (the A-191 engine) and the other, the A-221, the first of the famous double-rocker-shaft pushrod designs that would be later used on the A-182 prototype V-8 and the production 331-cid Chrysler V8 of 1951. This layout is on the 426 HEMI and all Top Fuel and Funny Car engines today.

In 1953 Cahill was assigned as a “motor engineer” to the Plymouth assembly plant on Lynch Road in Detroit. He got involved in special projects, including racing, because “I was interested in doing the work,” he said. Also, he was noticed because he did things such as installing a 1952 Chrysler HEMI in his daily driver—a 1950 Plymouth. “It wasn’t very good, nose heavy and under-tired, but it surprised a lot of Olds Rocket 88s,” he said.

He was involved with the Mobilgas Economy Run and the Union Oil Performance Trials. Meanwhile he took an engineering team and a 1956 factory-prepped Plymouth Fury to Daytona Beach for the annual speed trials in January 1956. Phil Walters (a factory driver for the Cunningham sports car team and widely known as “Ted Tappet” in midget racing) blew through the Flying Mile at a record-setting 124.01 mph.

In 1958 and 1959 Cahill had a B-engine big block 2-door hardtop Plymouth that he drag raced. The car was “mistakenly” built with a 383 cid engine instead of the 350 cid version that was supposed to be installed at the plant. The “mistake” happened because Cahill was able to warp the system into putting the big engine into his Plymouth. He developed the car at the Product Planning garage across the street from the Lynch Road Plymouth plant, trying various rear axle ratios and other setup combinations.

Cahill returned to the General Office Building in 1960 as a product planner. Each division had its own Product Planning department. He served as a chassis and engine engineer. He was soon involved in drag racing and road racing. One of his first big projects was the Plymouth Valiant “Hyper Pak” for NASCAR racing in 1959. Tom Hoover developed the 170 cid engine at Chrysler’s lab in Highland Park, Mich. Hoover was in the engineering department, in charge of racing engine development. He eventually came to Product Planning under Cahill.

Hoover said, “We got just under 200 horsepower with 11:1 compression, tuned exhaust and a ram manifold (17-inch branches, based on some fuel injection work we did earlier) with a Carter 2948 AFB carburetor. We also had to add a second surface treatment to harden the oil pump drive bevel gear. Valve sizes were stock. If the program hadn’t ended we were going to increase valve sizes and use shorter intake runners. We had already built a fabricated steel manifold with 14-inch runners.”

Cahill personally hauled all the special parts for the Hyper Pak cars from Engineering’s inspection department to the Plymouth Product Planning garage in Detroit, where six cars were built for the upcoming races at Daytona. The cars were converted from standard Valiant sedans. They had upgraded engines as well as modified transmissions, rear axle ratios, suspension, tires—and they had semi-metallic brake linings.

After each car was built, Cahill and Ronney Householder (Chrysler’s circle track racing manager) drove them around Detroit to make sure they operated properly. It was January, so the cars, built with no carburetor chokes and the above-mentioned metallic brakes, were a handful to drive. Engines would not run cleanly until fully warmed and the brakes had no stopping power until hot.

Householder actually drove one car from Detroit to Daytona Beach with his family as passengers. “That must have been interesting,” said Cahill in an understatement.

There were two heat races scheduled at Daytona for compact cars— Plymouth Valiants, Chevrolet Corvairs and Ford Falcons. They would be run back-to-back, first on the road course and then on the banked speedway. NASCAR hoped this new class of racing would be the next big thing, because the cars were expected to be very popular in the U.S. as Detroit’s answer to foreign competition.

NASCAR hot shoe Marvin Panch led a parade of five Valiants as Plymouth blew the Chevvies and Fords away. But while he was on the victory podium kissing the race queen, the second race parade laps started. By the time he got his car out of the pits the race had started. Nevertheless he was in the lead within a short time and ran away with that race as well. Unfortunately this dominant performance by the Valiants killed the new NASCAR series.

Though Cahill gravitated toward drag racing, NASCAR was more important to Chrysler. The company made money from drag racing parts sales and used it to support NASCAR programs.

Cahill wrote the official Product Planning Letter to Engineering that kicked off the 426 HEMI project. Bill Weertman was the design engineering leader on the project. He said, “Bob Cahill had knowledge of the original 1951 HEMI as a development engineer.” Jack Charipar took it to senior management to make it official late in 1963.

That was the year Chevrolet introduced the “Porcupine Head” 427 “Mystery Engine” to NASCAR. It dominated the 1963 Daytona 500. Chrysler’s wedge engine just wasn’t powerful enough to compete.

When the 426 HEMI program started, Cahill believed that the engineers would need some help. “It was ticklish to tell Engineering that they didn’t know enough about racing engines,” he said. So he and Jack Charipar decided they would ask Harry Weslake for help. Harry was the premier engine air flow expert at the time, and had actually worked on the cylinder heads that won at Le Mans in 1929 (Bentley) and 1969 (Ford’s Gurney-Weslake heads).

With the help of fellow Chrysler engineer Chris Kennedy they set up a meeting among themselves and Tom Hoover with British speed parts guru Vic Derrington. Derrington put them in touch with Weslake, who flow-tested the 426 head and suggested important changes to the porting and combustion chamber. Weslake also did development work on other Chrysler engines, according to Cahill, including the Plymouth P-69 project. This was a fuel-injected small-block pushrod engine for the 1969 Indianapolis 500. Money came from the NASCAR budget earmarked for Richard Petty.

When Petty jumped to Ford, Weslake got the project, which included supplying the cylinder heads. It was January, 1969. He started work in February and delivered parts by April. The engine would be used by Andy Granatelli’s team in the STP-Lotus all-wheel-drive car that nearly won the previous 500-mile race, powered by a turbine. The car failed to qualify, however. It did finally win an Indy-car race later that year.

Bob Cahill retired from Chrysler in 1975. He lived for a while on St. Thomas in the U.S. Virgin Islands, but moved back to the states after a few years. At age 92 he is still interested in new automotive technology. He’s had two hybrid cars and is now driving a performance car with a six-speed manual transmission. “Enough of the old-lady cars,” he says. “I’m a young guy and I need something exciting to drive.” He’s currently waiting impatiently for Chrysler to introduce a diesel car for his next technological adventure.