D-Port Exhaust Heads For Pontiacs

The KRE aluminum D-ports are a simple swap-the only oddity is the special-length bolts, but ARP makes them. We had to use roller rockers, but we kept the ratio the same. Don't try to tell us these made the 40hp difference.

Kauffman D-ports
The KRE heads swapped on easily, using the application-specific ARP bolts and another set of Corteco gaskets. The 85cc chambers should have raised the compression to around 9.8:1-less than the full point of increase often recommended when switching to aluminum, but a nice safe pump-gas ratio nonetheless. This time, due to the larger rocker studs of the KRE heads and some poor planning on our part, we used a set of Comp Cams roller rockers, though the ratio remained at 1.5:1. With the fresh synthetic lube we were using and the relatively mild cam and resulting sub-5,000-rpm engine speeds, it seemed unlikely that an appreciable power advantage would result from the rollers, so we pushed ahead. The same induction, exhaust, and ignition components were returned to the 455 for the aluminum-head tests.

When the 455 was running again, we didn't expect to notice much difference outside of the dyno readouts after the pulls, but the engine seemed crisper on tip-in, and more willing to rev. Moments later, the confirmation was on screen-the 455 was up significantly. We'd backed the timing up to 34 degrees to be safe, but putting more lead in made no more power. In fact, the engine wound up happiest with a mere 33 degrees-an indication that the revised chambers were indeed more efficient. Once we found the best tune and made some back-up pulls, our calculated average peak power figure came in at 427 hp at 4,500 rpm and 540 lb-ft at 3,700. Just shy of a solid 40hp gain coupled with 45 extra pound-feet of torque.

Dyno Dyno
Test 1 is the 455 with 7K3 factory iron heads (96 cc), Comp Cams XE274H cam, Edelbrock Performer RPM intake, Speed Demon 825-cfm carb, and Summit four-tube full-length headers. Compression is 9.2:1 and total timing is 37 degrees.

Test 2 is the 455 with the KRE aluminum D-port heads (85 cc) and all of the same equipment used in test 1. Compression is 9.8:1 and total timing is 33 degrees.