Not completely true Jan. The 2.5" to 2.25" trasnition on the R with a JDM collector header is not all that detrimental. you will see a slight gain to use 2.5" all the way through but nothig to write home about 1-2 hp. he stock ITR exhaust will make all motor power up to 190 with stock cams (Has been done).

You CAN get an adapter that you weld into your b'pips that bolts to a 2.5" collector and that trasnsitons down to 2.25" but if a 2.5" exhaust makes a couple HP expect this to make les than 1.

The Toda header is a great choice. I made 180 whp on stock cams and stock exhaust with the OEM JDM 4-1 and a toda should make a bit more.

Trey