Something I'm not sure of

Do HKS center/rear sections come in different sizes.

I'm looking to purchase a HKS Hiper - imminently and want it to mate to a special 3inch Scoobysport downpipe.

The chap selling me the HKS Hiper has taken it off and said, that externally its 3inches, internally its 2.5 inches and narrower at the downpipe to mate to the typical 2.5 inch OEM downpipe.

How does a 2.5 inch mate to a 3inch downpipe - or am I just being stupid - surely taper would cause restriction??

So my questions are:

Are there a couple of different HKS sizes -i.e are there different ones that mate to 3 inch and 2.5 inch downpipe.

And when we say 2.5 inches do we mean internally or externally.

 

Steve if thats the case it's NOT a Hiper which is 3" all the way back.

 

Thanks