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| The 455 H.O. of 1971-72 combined the Ram Air IV’s cylinder head design with the extra displacement of the 455 V8; a great combination. |
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| Beginning with the ‘68 Ram Air II, Pontiac’s hottest V8s received new heads with round exhaust ports. |
(continued from pg. 12) 1969 also saw a very unique Ram Air V development program. This program actually consisted of different engine sizes utilizing a special cylinder head designed for racing. This head featured very large intake ports with pushrod tubes running through them (commonly called tunnel ports; Ford had one also). A 303 cubic-inch engine was developed for SCCA Trans-Am racing, along with a 366 NASCAR version. (NASCAR was changing their rules to allow small blocks with a 366-inch limit run unrestricted carburetors, while 7-liter, or 427-inch, big blocks had to use restricted carbs.) A 400 cubic-inch engine was also built, and as many as 80 of these engines were sold over the counter. Plans to install the 303 in the ‘69 Trans Am never came to fruition due to teething problems with the engine, and supply problems with the special forged connecting rods. While a few Ram Air V-based engines are in circulation, none were ever installed in production cars.
It’s fitting that Pontiac, credited with starting the muscle car movement, would fire the last shot in the super car wars with the Super Duty 455 of 1973-74. When most car companies were turning their attention to increasing fuel mileage and decreasing emissions, Pontiac offered the SD 455 in Firebird Formulas and Trans Ams. This engine used a modified version of the Ram Air IV cylinder head, although with much larger combustion chambers to keep compression down to 8.4:1. Low compression ratios were needed to allow the engine to run on unleaded fuel, a GM
mandate for all their car engines by this time. A specially reinforced block with 4-bolt mains, a nodular iron crankshaft, and special forged rods with 7/16” bolts made for a very stout bottom end. With 2.11” and 1.77” valves, a relatively mild cam with .406” lift, 301° and 313° duration, and the aforementioned low compression ratio, the engine didn’t look to be a ground-pounder on paper. The secret, however, was in the head modifications. The engine breathed very well, and although rated at only 290 net horsepower (net ratings were now being used by most manufacturers since they more closely related the output of an engine as installed in the automobile, pulling all the accessories, etc.), produced enough power to get the relatively heavy Trans Ams and Formulas in the 13 second bracket at the drag strip. With a cam change and a set of headers, this engine was really a beast. |
