fast intentions 12 or 18 res help??

Scribe

My FI exhaust has 12" resonators and drones between 1.5-2.5K rpm (which is kind of where you drive when you aren't laying into it). I don't know for sure that the longer resonators will help, but it may make the drone quieter. Other exhausts incorporate designs/tubes that eliminate the drone.

If you don't drive your car daily or aren't concerned about drone, the 12" is loud but not to the point where I worry about coming home late and annoying my neighbors.

I think the resonator sections are interchangeable (Tony can confirm). If so, you can always change them later if you are unhappy.