Hey guys i have an 04 Z, i recently ordered a stillen hfc and i wonder whether the cats would fit perfectly onto a stock 04 y-pipe? thanks in advance.

 

yes it will fit, the flanges will bolt up just fine..

however, take into consideration that the stillen hfc probably uses an inner piping diameter of 2.36" or 2.5" and the stock y-pipe is ~2.14".

So even thought the fitment will bolt up, the exhaust flow not be perfectly even. I am running Berk test pipes (2.5" inner diameter) into a stock HR y-pipe (2.25" inner diameter) and I have a pretty nasty raspy sound when my revs get up to 2.5k rpm. But it goes away after I get past 3k rpm.

 

Catalytic converters and test pipes all fit. Is the inner diameter the same? Not certain but it will be OK.