D-Port Exhaust Heads For Pontiacs

The KRE aluminum D-ports are...

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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.

	TEST 1		TEST2		DIFF
RPM	TQ	HP	TQ	HP	TQ	HP
2,500	450	214	465	222	15	8
2,600	448	222	462	229	14	7
2,700	452	233	466	240	14	7
2,800	456	243	477	255	21	12
2,900	461	255	490	271	29	16
3,000	469	268	502	287	33	19
3,100	476	281	511	302	35	11
3,200	485	296	519	317	34	21
3,300	489	307	526	331	37	24
3,400	492	319	531	344	39	25
3,500	494	329	537	358	43	29
3,600	493	338	539	370	46	32
3,700	492	347	539	380	47	33
3,800	490	355	537	389	47	34
3,900	487	362	535	398	48	36
4,000	483	368	530	404	47	36
4,100	480	375	523	409	43	34
4,200	473	379	516	413	43	34
4,300	465	381	509	417	44	36

4,400	458	384	504	422	46	38
4,500	452	387	498	427	46	40
4,600	444	389	486	426	42	37
4,700	435	390	471	422	36	32
4,800	423	387	456	417	33	30
4,900	413	385	442	413	29	28
5,000	396	377	430	410	34	33
5,100	384	373	419	407	35	34

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