Camouflaged by an air cleaner, air-conditioning components, and what seems like an endless
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.
The SD-455 block was reinforced in several areas to increase overall strength for extreme-
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.
...and the rear of the block with additional material cast in as a provision for dry sump
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.
The SD-455 cylinder heads were similar in appearance to other round-port heads and can typ
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.
Pontiac engineers refined the intake and exhaust ports to promote maximum airflow. As seen
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.
Initial plans for the SD-455 included a cast-aluminum intake manifold similar to that foun
Skip McCully's Views
In addition to component development, Skip McCully's duties on the Super Duty project included tuning the SD-455 for maximum reliable performance while remaining compliant with federal exhaust-emissions standards. To find the optimal amounts of fuel and timing for the SD-455, McCully and an engineer from Delco worked together using an engine dyno with full control over fuel metering and ignition timing to test several combinations, until they found what produced the most power under full throttle conditions. The production settings of the carburetor and distributor were altered slightly.
To retain constant port cross-sectional area, any point seen as a restriction on standard
McCully stated that to prevent failure from detonation-related issues such as poor fuel quality and incorrect octane, total timing was reduced 1 percent from the point where the engine made peak power. For example, if a respective engine made peak power at 38 degrees BTDC, McCully and the Delco engineer would reduce the total by roughly 3.8 degrees (or approximately 4 degrees), then use that point as the factory spec. He further added that initial timing and primary jetting were primarily set to comply with emissions and the rate of distributor advance was a compromise of performance and emissions. And since additional advance at part throttle typically generates excessive hydrocarbons under light load, the vacuum advance unit was limited to provide enough advance to benefit, yet remain emissions compliant.
As many enthusiasts already know, the original SD-455 camshaft had the same specs as the 041 used in the R/A IV, and McCully confirmed several preproduction engines were built with it. His personal test vehicle, a one-off black Trans Am pilot car, was powered by an SD-455 with the 041-spec cam and a functional Shaker hoodscoop. In addition to normal driving duty, the car was also part of a test fleet that traveled to the Desert Proving Grounds in Arizona for factory testing. The joke within the caravan was that the SD-455 would require frequent stops for refueling, slowing progress. But McCully suggested the group forge onward and that he and the SD-powered Trans Am would catch them on the top end. To the surprise of the those traveling in the group, however, the SD-455 Trans Am averaged the second-best fuel economy the entire trip, only to be outdone by a much more sedate cruiser!
The SD-455 was one of only a few regular-production Pontiac engines to receive heat-treate
Once at the Proving Grounds and without any tuning after the long trek, the SD-455 Trans Am with its automatic transmission and moderate rear gear consistently ran the quarter-mile in just 13 seconds. If that weren't enough, the car was taken directly from the track to the emissions-testing station where the large-cammed SD-455 passed below the federal standards but without enough "cushion" to satisfy the emissions engineers. This cushion was a safety margin implemented by the emissions engineers between the engine's actual output and the federal standards, to ensure that 100 percent of the engines in that group were compliant once sent out the door.
To adhere to this margin, a camshaft with less duration and overlap was used. In place of the 041-style camshaft with 308/320 degrees of advertised duration, 0.470 inch net valve lift, and 87 degrees of valve overlap went a cam with valve timing identical to the 744 grind. Best known for its use in R/A III manual transmission applications, the 744 cam offered 301/313 degrees of advertised duration, 0.407 inch net valve lift, and 76 degrees of valve overlap. With less aggressive valve timing, power output was affected slightly--but not all negatively. Horsepower dropped from 310 with the 308/320 grind to 290 with the 301/313 cam, but torque increased from 390 lb-ft to 395 lb-ft, respectively.
Consequently, McCully strongly stated that under no circumstances were any SD-455 engines with the 041-spec cams ever released to the public, and any rumors of production engines shipped that way from the factory are false. He added that all the pilot cars and any of the test cars in the Pontiac press fleet with the noncompliant SD-455 were returned and destroyed. Not only were these cars typically handbuilt without a valid VIN, they also were not emissions or safety certified. Pontiac could have faced severe consequences from the federal government and potential legal suits if anyone was injured in an accident had they been released to the public.
...the issuance of Parts & Accessory Extra bulletins like No. 73-19, which states that by
Once the SD-455 was certified with the new cam, it was ready for production. But just when it appeared the car might finally hit the streets, it was further delayed by a recertification mandate affecting every Pontiac engine when the EPA found that part-throttle emissions were noncompliant. In March 1973, a running change was made, eliminating the timed solenoid that gave full vacuum advance and disabled the EGR valve in high gear after a specified amount of time. Only after this was corrected and the SD-455 recertified was the engine finally released for production in approximately late April 1973.
Pontiac sales literature from 1973 states the SD-455 was optional on Firebird, Grand Prix, LeMans, and Grand Am models. Already delayed once by the cam change and then again with the midyear solenoid change and recertification, it would have been cost-prohibitive to recertify the SD-455 for each model with such a late market introduction. Since the Firebird was gaining popularity as Pontiac's premier performance car, the SD-455 was limited to just the Firebird Formula and the Trans Am. And because of drive-by noise standards and to save costs certifying the engine twice, the engine was certified only once with a sealed Shaker scoop in place. Because of this, the only Formula to receive the Trans Am Shaker scoop were those '73-'74 models powered by the SD-455.
When asked how he felt the Super Duty 455 was compromised for production, McCully simply replied, "Compression, camshaft, jetting, and vacuum advance." He then stated that ideally he would have preferred to have the compression ratio closer to 10.25:1, a camshaft with 041 valve timing, slightly richer carburetor jetting, and as much vacuum advance as the engine would tolerate at light load for maximum throttle response. But none of that was possible. Overall, however, the SD-455 was much the way Pontiac envisioned it, and its performance speaks for itself. McCully also said excitement about the project within Pontiac was extremely high. From the engineers' perspective, it was an opportunity to showcase their ability and produce the best Pontiac engine up to that point.
Long-lead press information released by Pontiac as early as July 1972 stated the SD-455 wo
Nunzi Romano'S Influence
Another interesting point mentioned by McCully was the close working relationship he had with Pontiac performance legend Nunzi Romano of Nunzi's Automotive in Brooklyn, New York. Romano's reputation for making significant amounts of power using stock Pontiac components continues even today. McCully said he took notice of Romano's achievements and would routinely contact him for his opinion on a variety of projects, including the Super Duty 455. Oftentimes he would send Romano experimental pieces for testing and review and some of that input was used on the production pieces.
When asked about his involvement, Romano recalled discussing with McCully the oiling system and reliability of the cam gear with the 80-psi oil pump. Romano said the drag created by a high-pressure pump often led to premature cam and distributor gear failure. He said to prevent this, a 0.030-inch hole was drilled into the oil plug inside the block, which shot a continuous stream of oil directly on the constantly meshing gears. Though effective, the hole was small enough that a piece of foreign material or sludge buildup could potentially plug the hole and prevent the lubrication, which could cause cam or distributor gear failure over time.
Romano also recalled at least two Super Duty Firebirds in his shop for engine rebuilds because of oil-pressure-related issues. The extreme pressure generated by cold oil and the 80-psi pump blew the oil filter off the housing, which led to engine failure from lack of lubrication. To prevent this from happening after the rebuilds, he substituted a 60-psi pump and tightened the internal clearances--which not only seemed to remedy this problem but also the cam and distributor gear issues. Romano said because of the excessive piston clearance, the SD engines were quite noisy when cold. He even received calls from dealers and customers concerned that their SD-455 had problems internally, but he assured them it was normal.
Even without major delays for the 1974 model year, availability of the SD-455 was still li
Overall, Romano feels the SD-455 was an excellent engine capable of making plenty of power, and that it was obviously designed with total performance in mind. He said the cylinder heads are among the best Pontiac ever produced and that little port work is needed to make them any better for the street. Romano currently has four Super Duty Firebirds in his private collection. His Buccaneer Red '74 has been featured in HPP several times. It has generated quarter-mile trap speeds in excess of 105 mph in stock trim with sharp tuning, and 108 to 110 mph with headers, increased ratio rocker arms, a high-volume fuel pump, and a pair of slicks.
Ultimately, someone somewhere may disagree with any part of the information presented here, but considering that both McCully and Hicks were in the middle of the project making the decisions, we feel they are excellent sources with qualified credentials. After talking with them, we were not only confident we could lay some of the SD-455 mysteries to rest but we could also reveal and provide accurate insight on how the Super Duty evolved. Like its predecessors, it was a foregone conclusion that the Super Duty was going to be something special, but no one had envisioned SD-455 excitement would be as high today as it was more than 30 years ago. After hearing more about its development and production from a few of the engineers who were there, hopefully the Super Duty 455 saga will continue for years to come.
Special thanks to Mike Hicks, Skip McCully, and Nunzi Romano for their assistance.
*Pontiac service bulletins courtesy of General Motors