Wheels Classic Cars: The 1951 Chrysler HEMI

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Wheels Classic Cars: The 1951 Chrysler HEMI

Post by scottm » Mon Jan 07, 2013 10:31 pm


Wheels Classic Cars: The 1951 Chrysler Hemi
http://thechronicleherald.ca/wheelsnews ... ysler-hemi
With Chrysler's Hemi name having been revived and Hemi powered muscle cars taking on almost mythical status, it seems like a good time to review the Hemi V-8 engine’s background.

After the Second World War domestic auto manufacturers began production of essentially pre-war cars. But they knew they required not only new models, but new engines because some of the old ones had heritages dating back to the 1920s.

The work of General Motors' brilliant research head Charles Kettering on high compression engines enabled GM to beat other manufacturers to the punch with short-stroke, overhead valve, high compression V-8s for 1949 Cadillacs and Oldsmobiles.

Chrysler had to soldier on with its venerable old inline side-valve sixes and eights until it could design replacements. When its new V-8 arrived for the 1951 Chrysler it proved to be well worth the wait. Although displacing only eight cubic inches more than the straight-eight it replaced - 5.4 vs. 5.3 litres (331 vs. 323 cu in.) - horsepower was up from 135 to 180.

But the important comparison was not so much with Chrysler's former engine as it was with rival Cadillac's 160 horsepower V-8. It would be the first significant shot in the famous Detroit horsepower race of the 1950s and '60s.

Chrysler had one-upped General Motors by producing an engine displacing the same 5.4 litres (331 cu in.) as the Cadillac (it even had identical bore and stroke measurements) that developed 20 horsepower more.

True to its strong engineering heritage Chrysler did not produce just another overhead valve V-8 with conventional wedge-shaped combustion chambers. It placed the valves on each side of the combustion chambers and operated them through two rocker arm shafts in each cylinder head, achieved the combustion efficiency of hemispherical chambers without the cost and complexity of overhead camshafts.

Chrysler called it the 'Firepower' engine but enthusiasts soon nicknamed it the 'Hemi.' The hemispherical combustion chambers gave it what engineers call superior volumetric efficiency; breathing in more air per revolution produces more power.

It was a brilliant stroke and the Hemi soon began building a reputation for outstanding performance. Mechanix Illustrated’s car tester Tom McCahill smelled a winner and took a brand new Chrysler New Yorker V-8 to the sands of Daytona Beach in February, 1951 where he won the National Association for Stock Car Auto Racing (NASCAR) Speed Week trophy as the fastest stock American car. In spite of the rough and sticky sand conditions and a 'stiff 25-mile quartering wind,' he managed to average 161 km/h (100.13 mph) in a two-way run.

The Chrysler engine's reputation spread quickly. Wealthy American sportsman Briggs Cunningham was building world class sports cars in West Palm Beach, Florida in an attempt to win the renowned French Le Mans 24-hour race in an America car. He chose the new Hemi for his cars and hopped them up to 220 horsepower using four carburetors and higher compression. Power would ultimately go much higher.

The Cunningham only managed to finish 18th in its first Le Mans outing in 1951 (McCahill said it was due to the low octane gasoline provided), but in 1952 it finished fourth behind two Mercedes Benz 300 SLs and a Nash-Healey. In 1953 a Cunningham finished third, but would never quite achieve its goal of victory for America.

According to McCahill one of the modifications Cunningham used to get more power out of the Chrysler engine was Cadillac pistons! A different wrist pin placement in reportedly raised the compression ratio of the Hemi from 7.5:1 to 8.5:1, which increased power by almost 10 per cent. They were also lighter than the Chrysler pistons.

Even though it had to propel a heavy car - McCahill's New Yorker weighed 1,928 kg (4,250 lb) - with less than ideal aerodynamics, the Hemi engine gave the big Chrysler excellent performance. Road & Track (11/51) tested a Saratoga V-8 Club Coupe and recorded zero to 96 km/h (60 mph) in under 10 seconds and a top speed average of 166 km/h (104 mph). These were very good times for that period.

McCahill recorded 10.9 seconds for his zero-to-96 (60). Both testers obtained these times by resorting to manually shifting the sluggish "Fluidmatic" transmission.

In addition to its Hemi engine the 1951 Chrysler made another significant contribution to automotive technology in the form of hydraulically assisted 'Hydra-guide' steering. Power steering was not new; it had been used on trucks and buses for some time. But its passenger car use was pioneered by Chrysler.

The introduction of power steering allowed engineers to design steering gear that eliminated the compromise between steering effort and steering ratio. Power assisted steering was a significant advance both in safety and driving ease, and although overshadowed by the fabulous Hemi, further contributed to Chrysler's reputation for sound engineering.
'50s era HEMI wagon? That's sweetness!
Scott Moseman
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