Today I cut my pipes and inserted a 3" x 3 ring Car Chemistry insert. I installed the inserts with the cap(with the hole in it) on the inlet side, and packed the disks with steel wool.

Some photos.
time to weld.jpginsertIn.jpgcut.jpginsidepipe2.jpgpipe-insert.jpg

Results dB (no doors or body on car)

------------------------NO INSERTS-------------------INSERTS
--------------------min---avg---max------------min---avg---max-----------------AVG Difference
-----------------------------------------------------------------------------------------------------------
in car idle ----------81----89-----106------------ 84-----88----100-------------------- -1 dB
in car 2000rpm----87-----100----115------------ 88----- 93--- 112 ------------------- -7 dB
-----------------------------------------------------------------------------------------------------------
side of car---------76------90----102 -------------86-----92----109 ----------------- +2 dB (lumpy cam?)
side 2000rpm-----87------100-----115----------- 87-----88----90------------------- -7 dB
-----------------------------------------------------------------------------------------------------------
rear of car----------79----- 86 ----89-------------83----- 86--- 88--------------------- 0 dB
rear 2000rpm------89------100---115------------85----- 87--- 95-------------------- -7 dB

I have a set of 2.5" inserts on the way, I may attempt to put them in the j-pipes with no packing or cap