I bought the ceramic 4-1 because of CA's shitty strict smog policies, and because a stock D16 header was going for $250 on Craigslist at the time (needed a new manifold ASAP). I've had no problems with them thus far, and they did make the car smoother and quieter. As far as performance, I could care less, so I couldn't tell you.. this is my daily haha.