the merge portion of these headers is well done for the price the extension and flange are the issue. if you go in to the header with a grinder most of the restrictions can be removed. if original is not a problem, remove the extension, and tail pipe to muffler and replace with 2 1/4'' or 2 1/2'' . original exhaust on a 351c 4v mustang was 2 1/2 to muffler 2 1/4 tailpipe for a reference....Rocky's engine is @5oo+ hp 17/8'' pipe is way to small.
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