273 or 318 or both help
Almost forgot to mention something:
When mounting your 273 exhaust manifolds to the later 318 (FYI- your 318 truck manifolds will not fit or work in an early A body), you will notice that the casting around the exhaust ports are slightly different between the two engines- they changed slightly over the years-
Old heads:
New heads:
This can be an issue for 2 reasons-
1.) The later heads may or may not have an air injection port drilled into the pad (circled). If present, these need to be drilled and tapped to 1/4-20 and have allen head set screws Loctited in to prevent an exhaust leak.
2.) The extended pad of the later heads also causes interference with the downleg of the early 273 exhaust manifold at the #7 port. The extent of this interference can vary, but it will be there.
As tempting as it may be, the solution is not to grind away the offending portion of the exhaust port casting- there is a coolant passage just beneath the surface, and if you hit it, the head is scrap. I speak from experience on this. :( Some people claim to have gotten away with it, but I did not.
Sometimes (depending on the amount of interference) you may get away with using a double gasket to space the manifold out from the head to gain the necessary clearance.
More than likely, you may need to use a bare header flange as a spacer between the two surfaces in order to make things happy.
This will also require longer studs to be installed in the two end spots to accomodate the additional thickness. Use sealer on these studs, as they are "wet holes"- they extend into a coolant passage.
Almost forgot to mention something:
When mounting your 273 exhaust manifolds to the later 318 (FYI- your 318 truck manifolds will not fit or work in an early A body), you will notice that the casting around the exhaust ports are slightly different between the two engines- they changed slightly over the years-
Old heads:
New heads:
This can be an issue for 2 reasons-
1.) The later heads may or may not have an air injection port drilled into the pad (circled). If present, these need to be drilled and tapped to 1/4-20 and have allen head set screws Loctited in to prevent an exhaust leak.
2.) The extended pad of the later heads also causes interference with the downleg of the early 273 exhaust manifold at the #7 port. The extent of this interference can vary, but it will be there.
As tempting as it may be, the solution is not to grind away the offending portion of the exhaust port casting- there is a coolant passage just beneath the surface, and if you hit it, the head is scrap. I speak from experience on this. :( Some people claim to have gotten away with it, but I did not.
Sometimes (depending on the amount of interference) you may get away with using a double gasket to space the manifold out from the head to gain the necessary clearance.
More than likely, you may need to use a bare header flange as a spacer between the two surfaces in order to make things happy.
This will also require longer studs to be installed in the two end spots to accomodate the additional thickness. Use sealer on these studs, as they are "wet holes"- they extend into a coolant passage.
