im going to get the modern performance exhaust and down pipe but i want the one without the cat i am wondering how can i avoid not getting a check engine light to come on or if it makes that much more sense to get the one with the cat

 

Simply from their design, I would go with the MPx 3" exhaust. To eliminate the "Check Engine" light, get the O2 simulators that Casper Electronics makes. Here is a link to them at Jegs:O2 Simulators