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Pontiac 1973-1974 Cylinder Heads

No "H" stamp on early 1973 heads.
The May 7, 1973 changeover date is Motor Unit Number 709986 assembled on or about May 7, 1973
May 7, 1973 is the head assembly date, NOT the casting date.
Heads with casting dates starting around mid-March 1973 to mid-April 1973usually will have screw-in studs.
See: HPP 4X Head Article

Casting Date
Month A=January, B=Febuary, C=March, D=April, E=May, F=June, G=July, H=August, I=September, J=October, K=November, L=December
Calendar date 1 thru 31
Last digit of year 2=1972, 3=1973, 4=1974
Example D133 = April 13, 1973

Production Start is usually in mid-late August
End of Production is usually in early August
Head Casting is cast into center exhaust ports
Secondary Stamp is stamped into small machined boss as shown in picture
Combustion chamber depth measured from quench side.
Stud Boss Type refers to casting design around rocker arm studs.
Joined type has provisions for two screws to attach push rod guide plates
Individual type requires screw-in studs to attach push rod guide plates
A.I.R. casting refers to Air Injection Reactor (air pump) passage cast into head

1973 Start of Production 1973 End of Production Engine Casting Secondary Stamp Combustion Chamber cc Combustion Chamber Depth Advertised Compression Ratio Rocker Arm Stud Type Stud Boss Type Intake Valve Dia. Exhaust Valve Dia. Notes
Aug. 1972 May 7, 1973 350 46 none 96 0.300 7.6:1 Press-in Joined 1.96 1.66  
May 7, 1973 End of 1973 350 46 none 96 0.300 7.6:1 Screw-in Joined 1.96 1.66  
Aug. 1972 May 7, 1973 350 AT Calif. 4C none 98 0.300 7.6:1 Press-in Joined 1.96 1.66 A.I.R. casting
May 7, 1973 End of 1973 350 AT Calif. 4C none 98 0.300 7.6:1 Screw-in Joined 1.96 1.66 A.I.R. casting
Aug. 1972 May 7, 1973 400 AT Calif. 4C none 98 0.300 8:1 Press-in Joined 1.96 1.66 A.I.R. casting
May 7, 1973 End of 1973 400 AT Calif. 4C none 98 0.300 8:1 Screw-in Joined 1.96 1.66 A.I.R. casting
Aug. 1972 Sept. 1972 400 2bbl AT 4X 4 98 0.300 8:1 Press-in Joined 1.96 1.66  
Sept. 1972 May 7, 1973 400 2bbl AT 4X 4H 98 0.300 8:1 Press-in Joined 1.96 1.66  
May 7, 1973 End of 1973 400 2bbl AT 4X 4H 98 0.300 8:1 Screw-in Joined 1.96 1.66  
Aug. 1972 Sept. 1972 400 4bbl AT 4X 7 98 0.300 8:1 Press-in Joined 2.11 1.66  
Sept. 1972 May 7, 1973 400 4bbl AT 4X 7H 98 0.300 8:1 Press-in Joined 2.11 1.66  
May 7, 1973 End of 1973 400 4bbl AT 4X 7H 98 0.300 8:1 Screw-in Joined 2.11 1.66  
Aug. 1972 Sept. 1972 400 4bbl MT 4X 3 98 0.300 8:1 Screw-in Joined 2.11 1.66 Factory installed intake valve seals
Sept. 1972 End of 1973 400 4bbl MT 4X 3H 98 0.300 8:1 Screw-in Joined 2.11 1.66 Factory installed intake valve seals
Aug. 1972 Sept. 1972 455 4X 1 114 0.390 8:1 Press-in Joined 2.11 1.66  
Sept. 1972 May 7, 1973 455 4X 1H 114 0.390 8:1 Press-in Joined 2.11 1.66  
May 7, 1973 End of 1973 455 4X 1H 114 0.390 8:1 Screw-in Joined 2.11 1.66  
1973 All 1973 All SD-455 16 6H 111 0.390 8.4:1 Screw-in Individual 2.11 1.77 Round exhaust ports
1974 Start of Production 1974 End of Production Engine Casting Secondary Stamp Combustion Chamber cc Combustion Chamber Depth Advertised Compression Ratio Rocker Arm Stud Type Stud Boss Type Intake Valve Dia. Exhaust Valve Dia. Notes
1974 All 1974 All 350 46 none 96 0.300 7.6:1 Screw-in Individual 1.96 1.66  
1974 All 1974 All 350 AT Calif. 4C none 98 0.300 7.6:1 Screw-in Individual 1.96 1.66 A.I.R. casting
1974 All 1974 All 400 AT Calif. 4C none 98 0.300 8:1 Screw-in Individual 1.96 1.66 A.I.R. casting
1974 All 1974 All 400 2bbl AT 4X 4H 98 0.300 8:1 Screw-in Individual 1.96 1.66  
1974 All 1974 All 400 4bbl AT 4X 7H 98 0.300 8:1 Screw-in Individual 2.11 1.66  
1974 All 1974 All 400 4bbl MT 4X 3H 98 0.300 8:1 Screw-in Individual 2.11 1.66 Factory installed exhaust valve seals
1974 All 1974 All 455 4X 1H 114 0.390 8:1 Screw-in Individual 2.11 1.66  
1974 All 1974 All SD-455 16 6H 111 0.390 8.4:1 Screw-in Individual 2.11 1.77 Round exhaust ports