I got the 40 series original on my 04 Mountainer 4.6L v8.
Kept the stock exhaust piping, just got it welded in place of the old muffler.
Sounds AWESOME, i get looks all the time, plus I have BFG M/T's so its a very loud mounty,lol.
I have some video clips of me running thru some pretty deep sand trails, but they didnt come out good, i'll try to get some more.
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But the flowmaster is VERY deep at Idle, sounds just like any muscle car.
Once you hit the throttle it gets pretty deep/loud, then once i get past 2kRPM's it silences up alittlemore but still sounds good.
But at highway speed it does have a nice solid sound, and can STILL hear it in the background with music going at a low/medium volume.
If i crank the music up ALOT, i cant hear the exhaust, but i can slightly feel the vibration of it at certain RPM's.
JUST went thru State Inspection here i Jersey today with it....no problems.
If your in doubt, just go with Flowmaster, you simply CANT go wrong, it sounds extremely awesome on the v6 and v8.