You need to cut out a section of the front to rear subframe that the front mount bolts onto so the pipeing will clear. Then you weld angle iron or other steal under the piping to join the subframe back together. When you look at it from the side, instead of the subframe peice being straight, it will now have a U in it to dip under the down pipe. Search on Probetalk.com, there are pictures. Everyone does it just a little different.
Bill, 2003 3.5 SE Altima, Black with black leather, headers, full SS exhaust, lowering springs, adjustable shocks / struts, SCAFII, 20" wheels, SER Tail lights, Dual Halos around headlights, HID headlights and driving lights, Maxima Helical LSD.
2010 Maxima SV Prem + Tech package
2006 Vulcan 900 Classic