How does the pipe diameter affect performance? The reason I ask is, most turbos have less than 2" i/d outlet so any smaller would obviously affect flow, on the other hand too big will create lag.
My HKS is mainly 2 1/4" o/d, which at a guess would create a very small amount of lag, so would 2" pipework cause any flow problems as the i/d would still be slightly bigger than the turbo outlet i/d???

Cheers.