Well.. I've had a Flowmaster 40 series muffler SI/DO for about a year an half and I've just about had it..way too loud!. I told myself that i wasn't going to change it but now I'm willing to spend some bucks. That being said, I want to switch to a Magnaflow muffler because....

1. It seems to be a little less noisy

2. Also I've heard that it helps on your gas mileage as well.

Is this true? If so how much will switching this help out with noise level and mileage?

(2005 STX Supercab 4.6 V8.)

 

That is true, magnaflows are not quite as loud, but are deeper and way better sounding imo. I have had a 14" si/do maggie for about 3 weeks sounds great. It can be loud when merging (nice deep tone nothing obnoxious) but I have a light foot so I hear a nice rumble under most driving. My family & friends like it as well. I have seen an increase in mpg's seems to be .75-1mpg difference. The maggies do get a tad louder as their interior material gets pushed closer to the walls if I remember correctly. Mine has gotten a bit louder and since you have a Flow 40, I would say consider the Magnaflow 14"si/do because it will be a bit quieter but definetely noticeable. Btw, you would have way less drone with the maggies which is great (just a slight hum on the highway)

 

You will be better off swapping to a Magnaflow muffler. The straight through design and rock wool packing in the case cut down on the interior noise, give a rich deep note outside of the music that comes from the engine, and you will see a 0.3 - 0.6mpg increase if anything, barely noticeable, but the Flowmaster is helping economy a wee bit too over stock, just not as well as the Magnaflow.

I'll suggest you the 18" body Magnaflow. Its part #12288 available at summit racing, performance peddler, hot exhaust.com, edlebrock.com, and many others.

 

Thanks guys. I do love the sound of the Flowmaster but the drone on the highway is getting pretty bad. Passengers complain also. Ha

Appreciate it

 

Yeah they sound pretty good. I diss them alot but they're an alright muffler for the noise lovers and giving an engine a sound with attitude

 

Like ive said time and time again i think it all depends on where the flowmaster is mounted on the truck. I have my super 44 mounted almost to the bed and the drone is not hardly noticeable where as my brother in law has a 44 and its right under his rear seat and it drones bad. Just my .2 cents though

 

I agree with you on that. There are many variables: muffler palcement, tip placement, how the truck is performance wise: lower rpms I would think = less drone so a truck that breathes better will cruise at lower rpms I would think.

 

I just went from flowmaster si/do to a magnaflow si/so catback kit and am very satisfied with the sound...it's not too loud, but has a very nice rumble when you want it to.
not saying i didn't like the flowmaster either though...i loved its sound also, but was a little too loud - i got a great deal on the magnaflow setup that i couldn't pass up. I wanted the mandrel bent piping and liked the idea of having stainless steel muffler and piping, so i bought it. i bought the magnaflow used. It was 2 yrs old and looks twice as new as my 1 yr old flowmaster lol.

 

I ran a Flow 40 SI/DO for 3 1/2 yrs untill it rusted out. It sounded great at idle and when you mashed down it was plenty loud. Start up sounded crappy and had a slight drone in the cab at about 40mph. I went with the 18" Magnaflow SI/DO and noticed that it sound's real clean when you start up but has a quiet idle sound compared to the Flow 40. It's plenty loud enough for me when you mash down (almost as loud as the Flow 40) and at 40 mph there is no aggravating drone inside the cab. I'm well satisfied so far!