No open pipes will only cost you power since there needs to be some back pressure. Depending on the year of engine. The early mufflers had only 1/2" exhaust outlet. This would need to be opened to make a 1"-1 1/4" outlet. The newer mufflers have a larger outlet but many have a converter either inside the muffler or in the pipe just before the muffler. The mufflers supplied are very restricted so the object is to make them less restriced.
TOM
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