Several years ago, we spotted a Pontiac 455 in the Pick Your Part and nabbed it, knowing that it was getting increasingly difficult to find the biggest of the Poncho mills. The idea was simply to obtain a good core, but the subsequent peek inside revealed that the engine was actually in pretty decent shape. We cleaned it, tuned it, and ran it on the dyno, starting with the pathetic stock stuff from 1976, the final year of the 455, and ending up nearly doubling the engine's output with bolt-ons (see "Junker to Thumper," June '03).
The next phase was going to be the proper rebuild, but as we were procrastinating over that, more Pontiac speed parts continued to flow into the marketplace. Of particular interest were the relatively new Kauffman Racing Equipment aluminum heads. Once they hit the shelves, we got all hot and bothered to dyno-flog them, and being the impatient lot that we are, we didn't want to wait to freshen the big Pontiac, so we figured we'd set 'er up again and see if our mule could handle another dyno session. There were some fears over potentially wrecking our nice core 455, but we figured if we didn't get crazy, it would hold together one more time. It did, and we got our numbers. Want to see if the new aluminum D-port heads are worth it? Read on.
The Deal With D-Ports
In the world of Pontiac performance, there's pretty much one engine family to focus on: The V-8 introduced for 1955 and produced through 1979. There is no big- or small-block, with all displacements from 326 to 455 being based on the same block architecture; the only significant change to the design came for 1965, and this was a minor cylinder-head alteration that requires a corresponding intake manifold. Since most performance Pontiac engine builds are based on engines produced since 1965, this is usually a non-issue.
The only other major variation in Pontiac V-8s is found in the exhaust ports, and here you have a choice of round-port or D-port. Round-port heads are exotic stuff only used on the highest-performance Pontiac engines offered while D-ports are the standard fare found on everything else. The round-port first appeared for 1968 as part of the Ram Air II engine option for GTOs and Firebirds; the next year saw the introduction of the most desirable round-port factory head, the Ram Air IV. Subsequent use of round-port heads include the '71-'72 455 HO and the '73-'74 SD 455.
Previously released aftermarket heads for Pontiac V-8s, like those from Edelbrock and the Wenzler, use the round-port design. It makes sense that an aftermarket performance head would start with the best offered by the factory and get enhanced from there, but there are lots of Pontiac guys who don't want to have to change headers and possibly parts of the exhaust system. That may not sound like a big deal, but there actually aren't that many different headers offered for the round-port, and those that are don't cover all body styles. Guys who spent bucks to purchase reproduction Ram Air exhaust manifolds for D-ports, like those intended for the '69-'70 Ram Air III, are also not that happy about the prospect of having to shelve them-they don't come cheap. For these reasons and others, Kauffman felt a need existed for an aluminum alternative.
Edelbrock patterned its Performer RPM aluminum Pontiac cylinder heads on Pontiac's '69-'70 Ram Air IV casting, which used the round-port flange. The side-by-side comparison illustrates that the difference in exhaust-outlet design isn't just in the shape of the ports, but the flange bolt pattern as well. The Edelbrock version of the round-port is flat on the bottom, but the dark circles of carbon represent Pontiac's intended dimensions.