Inside the 455 Super Duty

In the Pontiac hobby, there are times we find ourselves trying to separate fact from fiction.

It seems if certain misinformation is spread far enough, it becomes accepted truth and is difficult to disprove. (Of course, once printed in a major publication, any doubts that it could ever be incorrect are erased!)

Many different engines and models have suffered such a fate, but few are as misperceived as the Super Duty 455. Introduced at a time when the performance-car market was beginning a downward trend, all the excitement surrounding the engine contributed to its mystique. But several myths, combined with general misinformation, obscured the truth behind one of Pontiac's most powerful engines.

While many Pontiac hobbyists are familiar with the Super Duty 455 and the information commonly found in factory sales and service literature, and in articles in publications such as High Performance Pontiac, rarely has any credible information about its development emerged. Though a few accounts have surfaced throughout the years, many stories remain with the individuals who were directly involved with the project.

We are fortunate to have spoken with two of them. These former Pontiac engineers held key positions in the Super Duty project, and both took time to discuss their involvement and share their firsthand experiences about the development and production of the SD-455.

Undoubtedly, numerous individuals had some form of involvement with the Super Duty project, but few were as instrumental as former Pontiac Special Projects Engineer Skip McCully. Along with a full staff of project engineers, McCully was responsible for developing the Super Duty components. The design was then presented to former Pontiac Engineer Michael Hicks, who held the executive position of manufacturing representative for the project. Hicks headed a specially assembled group of UAW manufacturing workers who, in conjunction with the Special Projects Engineering team, cast the production Super Duty components as close to the original design as possible.

Michael Hicks' ViewsAccording to Hicks, the Super Duty project stems back to the '70 model year with what was to be the top engine option for the redesigned '701/2 Firebird Trans Am. The Ram Air Super Duty, a high- performance 400 engine much like the Ram Air IV, featured round-port cylinder heads, a heavy-duty block, and forged internal components, allowing it to withstand high engine speeds over extended periods. Not to be confused with the Tunnel Port Ram Air V, the Ram Air Super Duty was cancelled just before the Firebird went into production, and the always potent R/A-IV filled the void.

With more stringent emissions standards from one year to the next, a new General Motors requirement for 1971 was engine operation on low-lead fuels. This meant a reduction of static-compression ratios typically in excess of 10:1 on most performance models to a GM-imposed maximum ratio of 8.5:1. With horsepower adversely affected by the compression loss, Hicks noted that Pontiac's solution to restore lost performance was to increase engine displacement. And as R/A-IV components were added to a larger engine with less compression, the 455 H.O. emerged for 1971. The Ram Air Super Duty was another casualty, and if it was to become a production engine, it too would require less compression. As displacement increased to offset the compression loss, the Super Duty 455 was born.

Testing of the Super Duty 455 began in 1970, and it shared many concepts with the Ram Air Super Duty. The four-bolt main block, which was cast at the Pontiac foundry, incorporated several unique features, making it better suited for extreme performance applications than typical production blocks. Its lifter valley received additional cross bracing, and the bulkheads received added material around the main saddles and oil-pan rails for improved rigidity. The rear of the block received a cast-in provision for a dry-sump oiling system driven by the camshaft, while a high-pressure, 80-psi, wet-sump oil pump was used in the oil pan.

Like the Ram Air Super Duty, initial plans for the Super Duty 455 included a forged-steel crankshaft, but it was ultimately rejected because of excessive cost. In its place went a standard-production, nodular-iron, 455 crankshaft. But rather than the typical finishing found on all other production units, Hicks stated the SD-455 crank received deep rolled fillets to increase overall strength and rigidity. Rolled fillets change the compression area of the journal by providing more side area for bearing contact, while the wider radius removes the sharp angle between the rod journal and counterweight, which could act as a parting line under extreme loads. According to Hicks, no additional treatments such as nitriding or shotpeening were ever performed on the SD-455 crank, contrary to what some sources have indicated.

Although cast iron was sufficient for the crankshaft, engineers saw the need for a connecting rod and piston capable of withstanding the most severe abuse. Michigan-based Continental Motors was contracted to produce a forged-steel connecting rod, while piston-specialist TRW provided the forged aluminum pistons. The rods were stock-length, forged-steel units that were heat treated and shotpeened for added strength while being checked magnetically for cracks several times throughout the manufacturing process. Pistons received a single-trough valve relief to boost compression and increase overall crown strength, while thicker piston skirts improved rigidity for high-rpm use.

The round-port SD-455 cylinder heads were similar to those found on the R/A-IV and 455 H.O. engines but with revised intake and exhaust ports for even greater flow. Pontiac engineers redesigned the intake port to maintain constant cross-sectional area, and the result was a noticeably wider and taller port just past the intake flange. The pushrod bulge, normally 0.150 inch wide, was reduced so much that the pushrod passage in the head broke into the side wall of the intake port, and a 0.030-inch tube was pressed in to prevent leaks. Intake-port height increased so much the valve cover and rocker stud holes both broke into the port roof.

Since SD-455 cylinder heads used replaceable cast-iron valve guides, material normally cast into the intake- and exhaust-port roofs to strengthen the area around the guide was eliminated. The result was smoothly contoured ports with shapes resembling those seen on professionally ported heads, with a noticeable increase in overall flow. Where standard-production D-port heads with 2.11-inch intake valves typically flow around 210 cfm at 0.550 inch lift, Super Duty heads flow around 240 cfm at the same lift point, or roughly 10 cfm more than an average R/A-IV or 455 H.O. head at the same lift.