you dont need a retune, but you wont be getting the full potential of them.

since it is already tuned, you should still deff see some improvements, but you can add more power with a retune.

 

what for changes in the sound of the exhaust could i expect with the highflow cats that come with the dynomax headers and my 14" single in dual out magnaflow ?

 

I run the same setup with a dynomax bullet and the exhaust got noticebly louder. It's about perfect for me right now, slight drone under load, which I like, absolutely screams at WOT, definitely a old school bb sound to it. At idle I can hear it lope a bit, stock cam lope anyhow

Once my gears are broke in I'm going to get some vids of the setup

 

my longtubes with no cats made a large difference in sound. Its more of full deep loud sound that you can hear from far away. It used to loud with just my cutout and stock manifolds, but it was only loud when you were close to it. Now when i get on it, you can hear it for blocks

 

wats the difference between shorties and the long tubes? is it just the size? also does the performance vary with either? im looking at the LPP headers for my Silvy =)