September 16, 2011
1961 Chevrolet Impala SS. Click image to enlarge
Article and photo by Bill Vance
When Chevrolet redesigned its full size cars for 1961, the “bat-wing” fins that had appeared in 1959 and been toned down for 1960 were virtually eliminated. And in a rare move for Detroit, it temporarily reversed the trend to larger cars. The ’61 Chevy’s 5,316 mm (209.3 in.) length was 38 mm (1.5 in.) less than the 1960′s, although the 3,597 mm (119 in.) wheelbase remained the same. It was also 61 mm (2.4 in.) narrower and some 23 kg (50 lb) lighter. As well, the wraparound windshield with its “knee-knocker” pillars had been almost eliminated.
With the revised styling came an exciting new addition to Chevrolet’s offerings: the SS (Super Sport) option on the top-of-the-line Impala. While externally there wasn’t much to distinguish the Impala SS from regular ’61 Impalas, there were clues: spinner wheel covers and double-S badges on rear fenders and deck lid.
Underneath it was a different story. Since the Super Sport’s goal was high performance, the base engine was Chevy’s 5.7-litre (348 cu. in.) overhead valve V8 with 305, 340 or 350 horsepower, and the real sleeper, a new 6.7-litre (409 cu. in.), 360-horsepower V8. This engine established the SS’s credentials, and even inspired a Beach Boys song entitled “409” (“She’s real fine, my 409…”).
The 409 was derived from the 1958 5.7-litre (348 cu in.) V8, originally designed as a truck engine. While the 348/409 carried over some of the advanced engineering features — such as stud-mounted valve rocker arms — used in the 4.6 (283 cu in.) Chevy “small-block” V8, it had a significantly different combustion chamber.
Slanting the cylinder block deck at 74 degrees to the cylinder centreline rather than the normal 90 degrees placed the combustion chambers in the block, not the head. The resulting flat cylinder head surface allowed larger valves, and the stud-mounted valves could be staggered, giving the engine its “porcupine” nickname. Although combustion chambers in the block had advantages, they apparently weren’t significant enough for long term use. When the 6.7 (409) was replaced by a 6.5 (396) in 1966 it would have conventional chambers.
The 409 was introduced in mid-1961 but not many were originally available. This changed for 1962, when horsepower rose to 380 with one four-barrel carburetor, or 409 with two four-barrels and other modifications, therefore achieving the then magical goal of one horsepower per cubic inch. It later exceeded this with a 425-horsepower version. The SS also got stiffer suspension, power steering and heavy duty power brakes, and special interior trim was part of the package.