340 Cylinder Head vs 318 Exhaust Manifold

[dibbons]

My factory 340 high-performance exhaust manifolds are in storage so temporarily I will attempt to use 318 exhaust manifolds. I was not sure whether to use the 340 exhaust manifold gasket (one piece) or the 318 manifold exhaust gaskets (3 piece). What I decide to try first was fabricate a 20 gauge steel gasket with the ports sized for the 318 (top & bottom in photo).

I will probably first try my custom steel gasket alone (without either of the fabric gaskets 318/340) and see how/if it seals.

 

[barracuda-67]

Please post how well this works! I'm interested in doing the same.

Other thoughts I had: I understand that welding cast iron requires a specialty shop; perhaps send the driver side manifold to get some extra metal welded on which would cover the opening.

 

[66fs]

I have run early A 273 exhaust manifolds with “72” 340 “J” heads. I ported the exhaust manifolds and used 273 gaskets with gold RTV. It worked fine, no leaks. What head castings are you running?

 

[barracuda-67]

I have run early A 273 exhaust manifolds with “72” 340 “J” heads. I ported the exhaust manifolds and used 273 gaskets with gold RTV. It worked fine, no leaks. What head castings are you running?

Nice to hear! I will check the head casting numbers.

I'm running 318 manifolds on a 1968 318 right now. I have 273 manifolds available but they are from a 1967.