I straight piped my FG….and then I didn’t.


2007 FG140, 89k miles, pre DEF, 10,000lbs.

During the pandemic I got bored, took the truck to the local exhaust shop, took out the crusty flex pipe and the (seemingly 100lb) giant muffler in favor of a 3” straight pipe exiting between the fuel tank and rear tire w/ a downward turn.
I had watched the Youtube films (even posted one of a Seattle area truck w/ a straight pipe.)

But I hated this while in the cab; sounded like a tractor w/ an exhaust leak. The ”jake” brake sounded like it was popping off just below my seat. The exhaust reverberated off jersy barrier and tunnel walls and simply didn’t sound good.

So today I took it back and had the shop slip in a 24” Magnaflow muffler (#12259). We kept the pipe exit in the same spot as I was concerned about exhaust infiltrating my vinyl cover over the bed where critters sometimes ride.

…Very happy w/ the results. It seems as quiet as ever. Oddly there seems to be a smidge more torque and slightly better acceleration and speed-holding on some of my local hills.

Lot’s of arguments about free flow vs back pressure but I surmise that the muffler slows down the widely spaced 4 cylinder puffs just enough to help scavenging….seems to run smoother but that might just be the peace and quiet….Much better at any rate.

Lesson learned: It’s never going to be a bada** sounding Cummins I-6 or Powerstroke V8. Might as well enjoy the quiet ride.


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Crazy Person
All that said, it's not truly a 3" exhaust system unless you replace the OEM dump pipe at the back of the turbo.
The OEM dump pipe squeezes down to 2 1/4", which creates a flow restriction right after the turbo.

When I originally changed my 2 1/4" exhaust to 3" I simply used a short conical length of pipe to go from the 2 1/4" dump pipe flange to the 3" pipe.
Recently I replaced the OEM dump pipe with a custom fabricated one, so now it is an actual 3" exhaust system.

Does that really make a difference? To be honest, I really do not know, but it's done now and I won't be changing it back.

Dump Pipe.JPG

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