We dyno'd a STOCK truck before and after an aftermarket 4" exhaust was installed, No difference in the HP. Dodge factory engineers design the exhaust for the stock horsepower they tested the vehicle at. Now when you want to add a chip is when the aftermarket exhaust is going to help, so if your thinking about a chip in the future, plan for the exhaust now. Simple rule, air in, fuel in, exhaust out, changing one effects the others. Going straight pipe becomes an option, a lot of people love the straight pipe sound and if it doesn't work for you buy an aftermarket muffler, it's straight pipe. Sounds like a Saturday, case of beer, power tools and laying on the garage floor under a truck. WHOHOO

 

Did you happen to test the difference between a 4" and 3.5" down pipe? I have been told there isn't much restriction in the 3.5".

 

No we didn't. We just did two runs, the stock system then installed the 4" aftermarket and called it a day. I'll see if I can dig up the two performance data sheets next week and post them.
A co-worker bought a 2005, the exact same spec's as mine, the previous owner did a muffler delete, it sounded really good, nice little rumble not as loud as I thought w/o a muffler would be. However his complaint was that he couldn't talk on his cel phone driving down the hi-way. He drove it w/o a muffler for a year, a couple of weeks ago we installed a Pacbrake muffler on it in my garage. All we had to do was use a sawsall to cut the old pipe and clamps off, the new one slips over the pipes, then tighten the two clamps. He says it brought the on hi-way rumble down and is much better for his discussions on the cel, but he says it's no where near as quiet as mine with the stock exhaust.

 

i run a 5 inch down pipe into two 5 inch aussie stacks on my 04 305 motor i saw at least a 200 degree drop and i can hear my turbo at idle it sounds cool

 

I almost bought an 04 305 standard cab with Silverline stacks and JESUS that thing was loud!!!!
I installed my 4" system on Thursday and that stock 6.7l muffler sure doesn't muffle much. I would estimate that it's a bit over 3/4 as loud as straight pipe. The benefit I can see is if I get hassled for it being loud I can point to the factory muffler and just play stupid. My wife says I'm great at that and that it seems to come naturally to me....

 

I have a 5" FarmBoy Diesel (Expandit) exhaust with a 5" Donaldson muffler. Love it and it's not too loud or too quiet.

 

DELETE!!! Im stacked and it's horribly loud, best friend is stock piped and hit is really no louder.

 

my stacks arnt loud cause there 9 foot in the air any way the 07 has mbrp duals with no muffler and its louder than my 04 with stacks