Side-exit exhaust questions??

I have a 2006 387 with a C13. It currenntly has dual rear stacks, which I was thinking of replacing the mufflers on. As I was looking the truck over, I also found a resionator under the cab (I just got the truck, that's why i just found it) and was thinking about just leaving the resinator and doing a 90 degree turn-out with the exhaust exiting between the back of the cab and the rear drives.

My concern is exhaust fumes in the cab. How many of you have under-cab or side pipes and does it make a big difference? My old FLD has a straight out the top like usual and I could smell the fumes bad inside the truck, and would preffer to not have that. Tho this truck is sealed much better than my old one.

If not, then I am going to remover the muffler under the cab, and go with the Pittsburg high-flow mufflers (my brackets are for a 11" wide muffler, so Donaldson won't work) and this is why I was thinking of going with the side exit as it would be much cheaper than the $300 for the new mufflers.

 

This is actually kind of why I got rid of the straight 8" on my FLD..... I would refuse to park next to a truck to idle as it was loud as hell and I didn't want to keep anyone awake. I'd always park with the stack facing an open field or try to park on an end. Not only was I worried about myself, but also other drivers. I guess I will just dump the cash on some new mufflers.

So i guess my next question is, what is the purpose of the extra muffler under the cab? Is it just for sound deadening? I may just remove it and replace the stack mufflers then, as I see no need for 3 #### mufflers. I'm sure it doesn't help with my MPG either having all that restriction