I own an 05 sierra ext cab. i have a flowmaster 40 series catback as well as kn intake. What can i do to make it louder but keep it street legal/pass emissions. I suck when it comes to working on cars/trucks i just love driving so i dont know anything about this kind of stuff so any help would be much appreciated.

 

highflow cats, you can get 1 chamber flowmasters, there pretty loud with stock cats, lt headers. thats all i can think of.

 

Speaking from experience here's what I"ll tell you:

High Flow cats won't do anything. I have magnaflow cats on my truck and they didn't do anything.

Headers-will make it a little louder but it will sound meaner

Your best bet is to ditch the 40 series flowmaster. I had a single/dual out 40 series and it sucked. I'm now running a single dynomax bullet and I'm pretty sure that's what you want. It sounds badass and is loud as hell when you get on it.

 

i seriously doubt that bullet is louder than a 1 chamber flowmaster. Have you ever heard a truck with 2 1 chambers and no cats?? sounds like a damn helicopter. I read a while back that the highflows dont do much cuz if im not mistaken we pretty much already have high flow cats right?

woohoo my 200th post

 

the stock cats are actually pretty good. unless your cats are about to goto **** I wouldn't replace em.

single chamber flowmasters are freakin loud. Im not running a muffler right now, but I have a super 40 that I'll bolt back onto my truck once it comes around to march for my first annual inspection

 

im running 3" flowmaster single chamber muffler. that being combined with my longtubes and no cats-it sounds very healthy. i would suggest leaving on the cats and changing to a louder muffler. i can get you some clips of my single chamber flow if you need.