RAM Air IV Cam Specsby Richard Rowe
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
- LT1 How-To: Camshaft Basic Specs and Concepts