So a while back i had a custom 2.5" ypipe made, the shop i went to simply sawzalled the ypipe out and reused the oem inlet and outlet flanges from the stock y pipe, my high flow cats are 2.5" outlets and my midpipe to the canisters is 2.5" all through, are the oem flanges on the y pipe causing any restriction?

im not sure what size the inlets and outlets are on the flanges i cant find any threads that have a solid answer. 05 oem y pipe flanges by the way.

Thanks

 

i believe that the oem exhaust is 2 1/4 inches, not positive but if so, yes you will have a little bit of choke point.

 

I think it 2 1/4