changing the factory muffler and installing a flowmaster, does anyone ever leave the single exhaust pipe coming out the stock set-up, or is it best to have the dual pipes leaving the muffler and coming out the rear?

 

Do yourself a favor and use the factory pipe. You will save $150 or more over a catback. You will lose the big heavy OEM muffler and keep the factory stainless pipe. You will probably have to add about a foot of extra pipe to fill the gap because the FM is much shorter than the stock muffler.

I would recommend a FM Delta Flow 40 or the SUV 50 Series (non-Delta) for nice deep sound and better performance. If you want quiet, go with a 50 Series Delta Flow or a 70 series. Good luck with whatever you decide.

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Howie's Effie
2000 F150 XLT Supercab Flareside
5.4L 4x4 with 3.55 L/S
Mods: Superchip, WMS Velocity Tube, Flowmaster Force II, Scorpion Spray in Liner, fogs + hibeams (thanks FedExPilot)

 

stoney- On a single in/dual out muffler, your output can never be higher than the 1)single pipe that feeds it. The first restriction the exhaust hits flowing from the engine back limits what's behind it. The dual outs vary looks and sound.

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2000 F-150 XL, RC, LB, 5.4L, 4R70W, 3.55LS,
Class III tow, Payload #3, & Convenience pkgs.,
4-wheel disc/ABS, Chestnut/Parchment 40/60,
Ford bedliner w/Paintsaver & gas/wheel/spare locks,
K&N F.I.P.K. w/Outwears pre-filter, Superchip,
Dynomax ultra-flow welded 3" cat-back w/ 3" Y-pipe,
Hellwig front & rear anti-sway bars, Rancho RS 9000s,
Mobil 1, K&N oil filter.