Originally Posted by semtex

No. The whole point of backpressure tubes is that, past a certain exhaust velocity, they're bypassed. In other words, they're variable -- they give you backpressure at low rpm (which is where you want it), but don't restrict flow at higher rpms. If you just narrow the piping, you lose that variability. These tubes are really no different than what HKS did on their exhaust for the 350, so I'm not sure why everyone is so puzzled by these secondary tubes. (Well, maybe people haven't ever seen the HKS 350 exhaust or something.)