The OEM exhaust on my truck was 2.5"; this will flow up to 300HP. Most aftermarket HP mufflers will flow approx. twice the OEM "garbage can" and up, are a nice upgrade (muffler alone) in performance. Most HP aftermarket mufflers will require cutting, welding, adding a small bit of custom bent pipe, and a hanger accommodation (they are not direct bolt-ins). Once you do this "installation" and buy the muffler, you will approach about half the price of a dyno-tuned application specific cat-back system. There are many nice aftermarket mufflers (just pick a sound). The multi-cat setup on these trucks cuts the sound output down substantially. My setup did not loose any low-end torque and gained mid and top power. I would not expect to gain much low end torque while opening up the exhaust. You are exactly right that the exhaust and intake mods compliment each other and are not fully utilized done independently. Good Luck !!

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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.

 

I was thinking about doing something with my exhaust but after reading some of these posts I dont know. I was thinking about replacing the stock muffler on my '98 extended cab w/ 4.6L with a flowmaster. I am looking to at least get some of that V8 rumble but nothing obnoxious. Also my big concern is people complaining of lost low end/torque. I definitely dont want to lose anything, I want to gain something. I would think that it would help with performance or mpg but some of these posts make me wonder. Should I just replace the muffler and keep the stock pipe (2 1/4 I think?). Has anyone replaced theirs with a flowmaster and noticed a gain? If so which series? Im open to any muffler, Ive just always heard good things about the flowmaster. Any help would be greatly appreciated because I really dont know anything about exhaust with these new engines. I also want to get a FIPK eventually and would want it to match the exhaust well and give me some enhanced performance. Thanks! (sorry for the book

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1998 F-150 Lariat,ext cab
4.6L
White w/ tan bottom
Full power and leather
4x2
hyper white running lights

 

Larry, I replaced my stock muffler with a FM 70 and am pleased with performance and sound. I chose the 1 in and 2 out(exit in front of RR tire). Also, kept the stock tubing(I think 2.25) to keep costs down. Looks and runs better. Improved gas mileage as well.

 

I just installed CGS Motorsports' single 3"inlet, dual 2 1/2" outlets on my 5.4L. This is the only muffler that I am aware of that is designed for low-end torque and power. Flowmaster, Magna Flow, Gibson, etc. are designed for performance at high RPM's. That's why you hear a lot of people complaining about loss of power and torque with these mufflers. How many of us actually run our trucks in the 5K to 6K RPM range? CGS Motorsports' muffler has a great deep sound without any drone in the cab. It also has a lifetime guarantee unlike Flowmaster and Gibson. Check out their website or give them a call, "www.cgsmotorsports.com"