WHats a 2.5" diameter exhaust good for power wise before needing to go to 3"?


In contact with the new owner of my old ST and turns out my drunken eBay purchase was a 2.5" cat back not 3".

Plans are for a 3" down pipe as he just fitted a 3" decat. Is there any need for the cat back to be binned off for a 3"?

Thanks, Carl.