I didnt say it he did

They are made to bolt up to the HKS cat back and yes it does go with the apex because they are made by the same company.

 

HKS bolts up fine to the stock exhaust, so I would imagine it wouldnt have any problems with others out there with larger diameter flanges that would fit better. (HKS is a 3" Flange)

Most exhaust systems are not full 3" as to provide a better fit to the stock downpipe. For those buying an HKS dp, more power would be realized when mated to a full 3" cat-back. Not sure which, if any exhausts are designed like that.

 

I had the downpipe on my stock cat back, and now with an APEXI N1 cat back, and have 0 problems.

Nick