[Tr6]

A couple things people seem to miss is... especially with aftermarket catbacks. You absolutely HAVE TO CUT the pipe right before the muffler or flatout cut the cats out.

Stock exhaust = shorty triy headers, primary cats and xpipe WITH axleback. There are only 3 parts to it thus if you take out the secondary cats you don't have a single option but to cut the stock catback at some point. Unless you absolutely get an axle back with xpipe (full catback) combo but not if you wanna keep the stock axleback.

Given you leave stock headers and primary cats alone... In order to replace the secondary cats, you have to either just "surgically" remove them or when you get an xpipe (like me, I have borla catless), you remove the front part that just bolts on to the back of the primary cats and then CUT before the muffles for welding/clamp.

Another thing. SS stock exhaust (also C7s) are 2.75' and you really want to keep the parts you replace that size. LT1 is absolutely perfect with 2.75' exhaust. Going 2.5 or 3 actually hurts and doesn't benefit anything (feel free to look for Borla's research on this as well as talk to Chevy engineers if you see them at an event) where as LT4 (ZL1 and Zo6 AND Ctsv) has 3's all around because that's what the engine works best with.

Also, when replacing secondary cats... Especially on manual, as long as you don't have any leaks due to install (make sure the welder uses an arcing welder and not straight one because he won't be able to weld the top of the pipe thus causing a leak and that leads to CEL) you won't have any issues. I've had mine installed almost a year ago now and zero CELs. As for the A8, you may have to reset the AFM parameters by disconnecting the battery and all. Not sure how it works as I have an m6 but feel free to contact the exhaust manufacturer and they will guide you on how to.