Edelbrock Olds Heater Plug 1PrEdelbrock part #2733 Oldsmobile Replacement Cast iron Exhaust Crossover Plugs. These steel plugs are furnished with each Performer 455 manifold and must be installed in the exhaust crossover port in each head. These plugs prevent cracking of the manifold caused by extreme heat of the exhaust during extended periods of Wide Open Throttle. Use a file to finish and fit the plugs until they are a light drive fit. Warranty