..well an open exhaust, from my prsonal experience, does INDEED make a difference in a 4t...
..i drilled holes in my oem pipe, along with a free-flow air filter and proper re-jetting of the carburetor, i'd say it's the only way to roll!!!
..and it's true, you must match the pipe with a 2t's capabilities...
..but on a 4t, any increase in air flow through the engine is a major plus!!
..i would not suggest installing an aftermarket exhaust without also installing a free-flow air filter...
..doing so makes your scoot extremely difficult to tune....
peace