[Modena]

slowy, 1 & 3/4" primaries are ample for your motor. Shorter primaries will give you better low down torque, longer will give better high-end power. A x-pipe balances the flow and (allegedly) gives more power as it can create a bit a venturi effect and give greater gas speed.

If you did put a blower on you would probably want to be at 1 & 7/8" primary size depending on boost and power levels.

I used 1 & 3/4" on my 6.2L, this is a 340kw motor from the box. For a non race-car low down driveability wins hands down over top end power.

As you have asked about a balance pipe I guess you're talking about an under-car system?