I update a previous posting with a clearer presentation:
I have reviewed a selection of OEM intake manifolds to help answer some questions regarding individual variations between the years from early 1966 through 1970. I reviewed samples of these manifolds for each production year so I feel confident the gamut of variations is pretty well covered. Each of the manifolds has a date of production cast into the body except for the sand cast version. Surely there are manifolds with 1967 date codes and conical outer runners to coincide with the design change. I assume the oblong outer runner cross section was an attempt to accelerate air flow to help make up for the longer runner length.
The finishes on the manifolds shown are not OEM.
Info presented in no particular order:
• All manifolds are magnesium; earliest is sand cast and all others are die cast and have date codes
• sand cast, w/o mfg date; manifold part number: 901.108.321.01 with oblong outer runners; 34mm
• die cast, 1966, 911S manifold has part number: 901.108.321.0R with oblong outer runners; 35mm
• die cast, 1967, 911S manifold has part number: 901.108.321.0R with oblong outer runners; 35mm
• die cast, 1968, 911S manifold has part number: 901.108.321.0R with conical outer runners; 35mm
• die cast, 1966, 911N manifold has part number: 901.108.321.1R with oblong outer runners; 34mm
• die cast, 1967, 911N manifold has part number: 901.108.321.1R with oblong outer runners; 32mm
• die cast, 1968, 911N manifold has part number: 901.108.321.1R with conical outer runners; 32mm
• die cast, 1969, 911N manifold has part number: 901.108.321.1R with conical outer runners; 32mm
• die cast, 1970, 911N manifold has part number: 901.108.321.1R with conical outer runners; 31.5mm
• starting in 1967, reinforcing ribs extend from the bottom flange up the exterior of the runners; 1968 and later manifolds have larger and longer reinforcing ribs
• starting in 1968 the lug for the 8mm shaft for the bell crank has an added reinforcing web
• 1967 and later have ports for Sportomatic and/or other vacuum accessories
• The sand cast manifold was for the first few 911s supplied with Webers which began to appear in Feb 1966 with engine #907001 as the Solex carbs were phased out.
• The early (without reinforcing ribs) manifolds had plating and conversion coating the same as the early Solex manifolds.
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