My 2 cents...
David Berman has a 540 bhp motor (engine dyno tested) that dropped exactly 20% when installed in his GT5 and measured on a chassis dyno. This is pretty typical of every Pantera I have ever read of that has data for both the chassis dyno & engine dyno (19% to be exact).
David's exhaust system includes the stock GTS/GT5/GT5-S mufflers. I am confident in writing that these mufflers "unmodified" inhibit performance no worse than any muffler for a 550 bhp or less motor.
cowboy from hell
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