327sb no back pressure

i have a 68 Chevy c10 with true dual exhaust but when i cover one exhaust left or right no back pressure builds up until i cover both exhaust they are no tubes connecting each exhaust to each other it seems as if the exaust from one side some how makes it to the other side of the engine.there's no rough idle ,no back fire, nothing and i cant figure it out it makes no sense could i possibly have bad heads????? they're 882 heads by the way


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You only tested this at idle, right? Those heads have the exhaust crossover, so the real questions are what intake manifold is on there, and are the crossover holes open in the intake gaskets?

yes i only tested it at idle and how does exhaust cross over work Ive never heard of it and its the factory intake manifold with a Rochester 2bbl... so if i put in a dual plane intake with a 600cfm carburator will it even work???

It's an emissions device. It does nothing to help performance once the engine is warmed up, unless you live in Alaska. Go ahead and swap the intake manifold if you wish. Basic choices like the Edelbrock Performer 2101 will retain the crossover, which is great if you drive in really cold weather. If you live in Panama, then don't worry about the crossover, block it off for better performance.