I know the owner or someone in the Magnaflow company posts here I just can't seem to remember his name. My question is, I am looking to weld up some magnaflow cats (I already have a xpipe) but there are so many to choose from. All I need is the one that fits a 2.5 inch xpipe. I don't know what the difference between air and no air cats is. Any help is appreciated but a part number would be greatly appreciated. Thanks.