single exhaust for 318...what size??

Thats tough, everything we do is mathmaticly correct, to keep the exhaust speed high. Really what needs to be done is the collector needs to be cut off and then go from your 4 primary tubes straight to a 2 1/8" or 2 1/4" pipe using a merge collector. Those two pipes need to be merged into a 2 into 1 collector, then with your 3" outlet. If you truly have a 3" collector on the headers now you have to try and transition it slowly, like in a 3 degree increment to the 2 1/4" or 2 1/8" pipes, then to the 2 into 1 collector. The key is not to lose exhaust speed in the system.

Mark Lelchook
Performance Welding
Racing Headers