First plus: they really sound great above 4000 rpms. One racer who tried 180 headers said they bumped his mid-range torque up a bit, but cost him 600 rpm on the top end, probably from gas flow resistence in the very long pipes. On the downside, they weigh about twice what a good set of tri-ys or 4-into-1 pipes do, you really cannot run the rear trunk which makes road trips complicated, and if you think changing plugs now is troublesome, try servicing a Pantera with nice toasty 180 headers! They also radiate enormous amounts of heat from the lengthy pipes, absolutely requiring some sort of good heat-reflector between decklid and pipes, and maybe even requiring a carb box for cool air intake. We BOILED the paint in two coffee-can-sized spots on an unprotected decklid in a 25-mile high-speed run. As for predicting power & torque increases from a single part change, if I could reliably do that, I'd be telecommuting to Ferrari or McLaren's F-1 race teams at $10,000 or so an hour.... Sorry.
