I have long tube headers for my 318 that I'm wanting to install but will also need to redo the exhaust. What would you guys run for pipe size and mufflers and would you run high flow cats or no cats? I'm definitely waiting to go with true duals with tips.

 

2.5 inch pipe, with an H or X pipe close the front, for the O2 sensor. Mufflers of your choice, there are a fair few videos on youtube of different mufflers. Pick one that sounds good, as they have little, if any at all, effect on power. If you run cats, you want high flow.....

 

The main reason I'm asking is everyone tells me I need to run a muffler that will create some back pressure. Which I wouldn't think a glass pack would. I was thinking of a flowmaster 10 or super 44 but some say they sound like tin cans on a 318

 

so I have been looking and think im leaning toward an H pipe with 2 flowmaster super 44s (unless someone knows of a muffler that sounds better) into 3.5x22 inch long tips out the corners on 45s. I have also seen quite a few of them with 2.25 inch pipe all the way back,

 

Spend some time on Youtube. No yours won't sound identical, but you'll get a better idea what you like. I learned I hate the tone of flowmaster and like magnaflow and some others. Search for "dodge 318 flowmaster sound clip", or magnaflow or whatever. We put a Magnaflow #12568 on my daughters 350 Chevy with shorty headers and 2 1/2" dual exhaust. I want to use this muffler on my Dodge when the exhaust gets done. I'm gonna put shorties on it also. Everyone has their own noise level perspective. I think this muffler has a good deep tone while fairly quiet with normal driving. It talks pretty good with some RPM and WOT.

My experience is larger pipe has a deeper tone. Smaller pipe has a crisper cracklier sound.


X pipe built into the muffler

 

If you are doing duals on a 318 or a 360 then no need to run 3in pipe. Go with 2.25 or whatever size your headers are. The x/h pipe needs to be up front so the O2 can read both banks. I recommend running dual cats cause I can't stand smelling the rich fuel poison exhaust, the cats help reduce it quite a bit.