4 barrel to 2 barrel adapters, unless they are at least 6 inches tall, will permit LESS air flow than the two barrel. If 6 inches tall, they still will NOT allow more air flow than the two barrel, but can be used only if the two barrel is unavailable. The use of the adapter will NOT gain performance, and should be considered only for emergency use.
If you are going to install the 4 barrel, best to also install a 4 barrel manifold.
Jon.
