The exhaust is 2.25". I have the 1.4L. In my case I installed an exhaust cut out. It's basically a y pipe with one end left open with a shutter blade or a likewise actuator to close the exhaust again. This basically allows you to run "open headers" In your case with the 1.8 if you installed headers with this mod. The only reason I say that with quotes is because mine being the 1.4 is turbocharged so it does not have headers. But none the less, it's a great mod, especially if you get creative with it because you're given the ability to run the stock exhaust for quietness and you can also run an open exhaust with just the flick of a switch. Now, i would be careful with the chevy cruze exhaust system. I see burnt valves possible with the 1.8 running open headers, so if you install a cutout, see if you can run that back as a straight pipe or possibly a side exhaust? I guess I'm trying to say is that if yours is the 1.8, if you do this mod, proceed with caution to avoid a zero backpressure situation that could cause scavenging issues. I installed mine right snug behind the downstream o2 right after the downpipe. I can post sound later. Slight performance increase noticed. Havent dynoed, but I also have the K&N Short Ram intake so that can play into it as well