Pontiac's Ram Air IV engine was the fourth evolution of an engine that had helped to create the muscle car as we know it. Premiering in the 1967 Pontiac GTO/Firebird, the 400 cubic-inch RA-I produced 360 horsepower using a large camshaft, a bespoke intake and cast-iron exhaust headers along with unique cylinder heads. Two evolutions later, the incredible RA-IV used one of the most massive camshafts of the musclecar era to produce some of the lowest quarter-mile times of its day.
The RA-IV camshaft is a hydraulic flat-tappet camshaft with a dual-pattern design. This camshaft was essentially identical to the RA-II, which used one of the very first computer-designed camshafts ever to enter production. The RA-II camshaft's engineers used their computers to develop a powerful and efficient dual-pattern cam, meaning that the cam uses different lobe designs for the intake and exhaust-side cam lobes. The RA-IV's cam was nearly identical to the RA-II's, so it uses the same dual-pattern design as its predecessor.
Essentially, the RA-IV was an RA-II with a new aluminum intake manifold and 1.65-to-1 rocker arms. These rocker arms were about nine percent longer than the RA-II's 1.5-to-1 rocker arms, pushing the valves open nine percent further while utilizing the same camshaft. The RA-II/IV camshaft had 0.313-inch lift on the intake and exhaust lobes, which yielded 0.470-inch lift with the RA-II's 1.5-to-1 rocker arms and 0.516-inch lift with the RA-IV's longer rocker arms.
If the Muscle Car Era had a guiding philosophy, it was surely "bigger is better." The RA-II/IV's camshaft posted some of the most radical duration figures ever used for a production car. These cams would have made most small-block cars of the era cackle and lope like dragsters, but the RA-series' 400 cubic-inch displacement and "torquey" nature helped to tame the cam a bit. Although its advertised duration was a healthy 308-degrees intake/320-degrees exhaust, the cam's duration at 0.050-inch valve lift is what really set it apart. This cam came with an at-0.050-inch duration of 231-degrees intake and 240-degrees exhaust, which is almost impractically large even by modern roller-cam standards. As a frame of reference, the 1997 Firebird SLP's 330- horsepower LT4 engine used a cam with 203-degrees intake/210-degrees exhaust duration at 0.050-inch lift.
Lobe Separation Angle
The RA-IV's lobe separation angle was fairly wide, which is the only aspect of this cam that you could describe as moderate. The RA-II/IV cam's computer-aided design allowed it to use a conservative 113-degree LSA while still making good high-end horsepower. This wide LSA reduced valve overlap, which is a measurement describing how long the intake and exhaust valves remain open at the same time. Less valve overlap means better low-rpm torque and increased fuel efficiency --"fuel efficiency" being a relative term by 1960's standards. As a frame of reference, the similar but less-advanced RA-III used a cam with a 110-degree LSA, and the 1997 Firebird SLP's rollerized lifters allowed it to use a cam with a 115-degree LSA. This is telling, considering the fact that an 1969 RA-III Firebird got about 13 mpg while its 1997 equivalent could get close to 35 mpg.
- "The Ultimate American V8 Data Book, Second Edition"; Peter Sessler; 2010
- "How to Rebuild Small-Block Chevy Lt1/Lt4 Engines"; Mike Mavrigian; 2002
- High Performance Pontiac: 1970 Pontiac Ram Air IV Trans Am - Road-Rocket Resurrection
- LT1 How-To: Camshaft Basic Specs and Concepts
- Popular Hot Rodding: Understanding Cam Specs
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