318 vs 340 Exhaust Manifolds

[George Jets]

318 vs 340 exhaust manifolds, have a look.

 

[Treblig]

They might look similar but.......The 340 exhaust exit hole is over 2 1/4" while the 318 is only 1 5/8". Here you can see a 318 exhaust gasket versus a 340 gasket. The 340 gasket (silver) has much more flow (area) than the 318 (blue).