I just got a 03 Civic Ex coupe. I want to put a full exhaust on. I have no plans to turbo. So my ? is, can I go as big as 2 1/2 inches and be ok?

 

welcome to the forum. If you don't have to worry about smog checks a 2 1/2 in exhaust pipes are good, gives good tone and no restrictions. also a clear cat helps.

 

I do have smog checks where I live. So what would be the best thing to do?

 

because of the small engine if you go full 21/2 inch exhaust you will lose low end torque but gain high end which isn't such a good thing on a car that has barely any torque as it is especially if your just daily driving the car. also you will only gain maybe 9hp if your lucky which won't be noticeable especially if your car is automatic. if you go full exhaust you will lose your cat converter which will cause you to fail smog unless you weld on a cat. if i was you i would just get a catback exhaust system which will give you a better sound but allow you to pass smog. or just have a shop weld on a universal muffler. one of the best sounding catbacks for this car is the APEXI WS2 though its pricy but it will last forever and make you happy.

 

if you don't have the cash get this vibrant street performance universal muffler there 90bucks but have exceptional sound and quality side note stay far far away from ebay exhaust they will rust out and the cheap sound damping materials used inside will burn up and eventually became unbearably loud and embarrassing.