I bought two sets. One with the screen and one that said it had a mini cat built in. I put the ones with the screen in first since they arrived first and they worked. I found those on Ebay. I've had a few friends buy them from http://www.bigdaddiesgarage.com/ with the same good results. Its mainly just moving them further away from the stream that gets the results you are looking for. Old school spark plug defaulers without screens or mini cat material used to do the same thing.