Replaceing my Cat Converters
 

I have to repalaceing my Cat Converters in my 2004 Ford F150 STX 4.6L. I want to go ahead and go to an aftermarket Cat to possible improve my trucks performence, I just do not know what to go with. If anyone has any suggestions to what i should go with please let me know!

Take all 4 cats off and replace with 2 magnaflow high flow cats. You probably won't notice much of a performance gain but you will notice an increase of sound.

I live in NC and we have to pass emissions tests. Will that still pass the emissions test?

They are 49 state approved

Why are you replacing the cats?

I wouldn't exactly replace the cats and expect a big performance increase. OEM cats flow well, the only way to improve performance with exhaust is to do longtube headers.

He claimed to increase performance.

keep this going.
 

More info on these aftermarket cats please. I was looking at replacing all of my cats to cure this annoying rattle coming from my cats. About $1200 worth. I have an 04 F-150 STX 4x4 4.6L. Sound appears to come from the right rear cat. An annoying tap resonates when the motor is revved or on take off. Unable to hear the sound when traveling at road speed. Truck only has 87k miles. I thought this to be weird for a truck with such low mileage. Any info is a big help. Thanks guys.