I have a 2001 F150 5.4, and I am considering replacing the stock muffler with a three chamber flowmaster.

Question is: will I see an increase in gas mileage? How about an increase in performance?

Any help you-all can give will be appreciated.

Thanks,

WGP
Tulsa

 

the only increase you are going to see will be in sound. my flowmaster actually hurt my performance. it made my truck a dog off the line, i couldnt even spin the tires anymore. if you are looking for a good muffler with a nice sound. go with a short magnaflow

 

X2 the flows sound ok(like every other f-150 on the road) but they did not help the performance. With the intake, the truck ran better with the stock exhaust than the flowbastard, but gotta love that noise. The 14" maggie is great or any other *High End* muffler, as for the mpg's, I don't care what you do, the real world gain is maybe .5mpg period, and then If your like I am and have to hear this new found glory, then you will always get worse mileage.

 

I have a flowmaster 50 series on my 2001, 5.4, with the 24# injectors and a troyer tune it would spin the tires like crazy off idle (with 3.55 Limited Slip gears on 20" rims)

the flowmaster is the best sounding muffler, phil1608 has flowmasters on his supercrew and he's sub 11's in the 1/4 mile

 

The 3valve motors must respond better then the 2valvers then because I have a K&N intake on my 05 and I had the stock muffler cut off and a 2chamber 40 series installed and it was a big increase in power.I could punch the throttle from a dead stop and light my tires up posi compared to not being able to do it before.never noticed a increae in fuel because i couldn't keep my foot outta it.

 

You're not going to see a big difference with a muffler swap, regardless of what muffler. It's not until you get rid of the crappy, crush bent exhaust tubing and replace it with smooth flowing mandrel bends that you're going to see some gains...