Been done many times. Does not increase torque, power, gas mileage or much of anything other than a little more noise. If that makes you happy have a shot at it.
Read this by the man who knows.
http://www.zggtr.org/index.php?topic=175.msg1225#msg1225
Then why does the '
Man who Knows' say this (I read this in the link you posted):
Mufflers - Used Cobras, Holeshots, Staintunes. Prices will range from a couple hundred used to 600 for the holeshots. Generally only good for 2-3 hp at best, and some noise.
You'll accomplish the same thing by just drilling or punching out the baffle in your stock mufflers.I had my stock mufflers done years ago by Sunny Steve . I was expecting and maybe even worried that it might be loud(er). To my surprise the bike was much faster and quieter and smoother running. The only time I thought it was any louder was when I stood behind the bike and listened to it idle and thought it might be a tiny bit louder.
I should mention that Steve did the whole package for me at one time- Exhaust sprocket mod, 7th Gear Mod, carb clean and re-jet,bafflectomy and much more but the end result was a much smoother , faster quieter better running bike. Thankfully Steve talked me out of buying a set of Holeshots and had me divert my money towards a much better 'bang for the buck'.
2 to 3 horse power ,a little better gas mileage , little to no noise increase and for the cost of borrowing hole saw is a very good deal indeed.