In a junkyard I found a 68 Firebird 350 2bbl with a 3 speed manual trans. Complete car. The RH exhaust manafold has no heat riser valve. Never had one at all. The date matches the block and heads and the engine is original to the car. Did manual trans cars not have this heat riser valve? The engine also has a block heater and it really doean't get that cold here so perhaps the car came from Canada and was built for Canada?? Any ideas? I'm putting together a clone 68 350 HO 4-speed and I bought the manafold just in case. Thanks

mine has a original heat riser in the manifold an its a 68 4 spd. I'll bet its from canada; but, I can't see why no heat riser.

what is the casting number on the manifold?

Pontiac eliminated it in mid-year (4/68 actually). See this Pontiac Technical Bulletin: http://firstgenfirebird.org/dtb/docs/68-I-56.pdf

I wonder if it was eliminated for the reason given or because everyone complained that they rattled so badly? Many of us simply used wire to permanently secured them open so that incessant rattling would end.