i'm looking at getting a 2013 cooper John Cooper works with 208hp. I've seen the upgrades of intake, exhaust, muffler delete, intercooler. How much HP can the OEM motor hold?? Also maybe a turbo upgrade. my goal is reliable 320-350Whp

 

Hi there, there's a guy in the UK that converted his R53 to turbo. He's making 312bhp right now but is in the process of adding another 60+bhp. But he did make the internals bulletproof. He did a port n polish, upgraded the pistons and valves. Hope this helps.