my situation....

i have ek with stock 2.0 gsr piping 2.0 catylic convertor aftermarket b pipe 2.25 to resonator to exhaust

question: if the gsr header and catylic convertor are 2.0 and the b pipe resonator and exhaust is 2.25 would this affect anything as far as miles or power loss or anything? and does any ek stock come with 2.0 exhaust piping?

 

I don't think you would have a power lose because the exhaust size becomes less restrictice (small>big) on the flow of the exhaust gas. You would lose power if it was more restrictive(big>small). 99-00 Civic Si may have come with 2" stock, not sure though

 

I think GSR stock piping is 2inches. dx/ex are 1.75"...

You should have no problem with a stock gsr header/cat to 2.25 piping finish through.

I have a us type r header gsr cat/b-pipe/muffer on my hatch. bolted up perfectly

 

yup got it on last night everything is perfect
......
til i blew my gasket