D-port identification
With most D-port heads, they are identified solely by the code present across the two center exhaust ports. The exception to this are the "4x" and "6x" varieties of Pontiac heads. They came in a wide array of chamber, valve size and pressed or screw-in studs. We use the identifier on the location near the temperature sender to further identify the head application.
6x head applications:
~ 4 This was the 89cc chamber, screw-in studs, 2.11 intake and 1.66 exhaust variety, used on 350's and W72 400 "for more compression" (maybe
closer to 91 - 95cc)
~ 8 This was the 98cc chamber, screw-in studs, 2.11 intake and 1.66 exhaust variety, used on standard 400's (maybe closer to 101 - 107cc)
4x-4c-46 head applications:
~ 1H is the 4X 455 head.
~ 2H is a small valve 4C, engine code not determined.
~ 3H is a big valve 4X 400 head used on m/t engines (used specific valve
springs with the 067 cam).
~ 4H is a small valve 4X 400 head.
~ 5H is a small valve 4C head used on an AIR code 350.
~ 6H is a garden variety small valve 46 head used on the 350.
~ 7H is a big valve 4X 400 head used on the a/t engines (the same head as
the 3H except specific valve springs with the 066 cam).
~ 8H is a small valve 4C 400 head from a '74 AIR code motor.
(info provided by John V. on the Classical Pontiac board)
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