I am thinking about putting on a set of Magnaflow Mufflers on my 70 Challenger Vert.
It has a built 383 with a roller cam, KB pistons etc. 3 inch pipe all the way back and headers with 3 inch collectors.
The issue is I want it to sound good, but I need it to be not overly loud. I had flowmaster 40s on before. Way to loud.

It seems Magnaflow come in 14,18,22,and 24 inch sizes?

Anyone have any experience with Magnaflow and the sound level per size?
Thanks

I used a set of 3 inch I.D. 14x7 inch oval Magnaflows with the side inlet and center outlet mounted behind the rear end exiting at the rear bumper, it was fairly quiet at part throttle, not so at WOT Those muffs only slowed my car down minimally at the drags, .030 ET and .25 MPH in the 1/8 mile On my other street and strip car with a set of 2.5 inch turbo muffs with side pipes exting in front of the rear axle slowed that car down .8 ET and almost 9 MPH in the 1/4 mile If your main interest is quietness than longer is probally better My main interest was not being slowed down by the ehxaust and then getting busted for open exhaust and getting harrassed by the law on the street , that never happened thankfully I usally did look around carefully before throttling that bad boy to WOT though

I will be swapping out my exhaust this Winter on my Challenger and I am going to use the TTI 2.5" X-pipe assembly (no mufflers) but buying separately the Magnaflow mufflers. I have been bugging the crapt out of the Magnaflow Tech guy asking him questions and trying to determine the same thing as you, how loud will it end up?

Something that might help you is that I asked the rep to tell me which Magnaflow muffler would be louder between this oval and this round style:
#11226: 2.5", 4x9x14 oval
#12616: 2.5", 6dia x 14 round

His reply: ""They have almost the same internal volume, so they would sound the same."

That to me makes sense. So I am going to start with the 4" x 9" x 14" ovals under the seat with the stock TTi 2.5" exhaust running out the rear. I will start it up and see what it sounds like. My guess is that it will be fairly loud so then I will be looking at adding a pair of the 4" x 14" long round mufflers beside the gas tank to see if that helps out on the noise. After reading some threads of other members, I might need to use two mufflers up front and two out back to keep it where I want it. I think that it will be trial and error.

If you need the Magnaflow Techs email, pm me and I will get that to you.

Same issue. I talked to Tech guys at Magnaflow.
I told him compared to the loud tinny flomasters 40s I have under the seats what are my choices. I wanted something 1/2 as quiet with lower tones. he said go with the 18 inch ones. So I am going with the 11259s.
Also, I ordered some 3 inch tips that are similar to the stock RT ones.

I tried to do a step approach like you are thinking, but I was concerned with back-pressure and restricting the exhaust. I have a brand new built 383. I don't want anything to restrict it's breathing.

I had the flowmaster 40s on the car with 3 inch pipe over the axle. Way to loud. then I added the OEM round mufflers at the end. they are 2 1/4 pipe at the OEM muffler.
The results were just the right sound level. But the tone sucks.
Again, I was worried about the restrictions of two mufflers. So I am starting from scratch with one good sounding bigger muffler.

We will see next week.

The OEM mufflers are horrible for performance as they are a huge restriction
(175cfm range). I run the OE mufflers and I can't wait to remove them.
Magnaflow mufflers are all straight thru so I don't think that adding more in line with each other would be a restriction issue. But the second one might change the tone.

Mount them as far back as you can,(to make them quieter ) mine where in between the outer fenders and the inner sub frames mounted behind the rear end exiting from the rear of the mufflers directly in front of the rear bumpers

I put 3 1/2" Magnaflow race mufflers on my Dart with 3 1/2" pipe exiting in front of the rear wheels. Sounds 1,000 times better than the Flowmasters I had on before, plus they really are not that loud until you open it up. I'd rather have them out the rear, but no room. Also when I go to the track, I don't take them off. That way you can actually hear yourself think in the car.

I am also leaning towards mounting the TTi 2.5" X-pipe assembly (muffler delete pipes) with the aftermarket SS 2.5" tips, and then starting in the back with as big of a round MF muffler that will fit. From the rear of the car, a 6" would fit but since they are Center/Center outlets, the 6" muffler will set down lower and will be seen easier from the rear of the car. A 5" round muffler will fit much better with less muffler being seen from the rear but there is only one selection of 5" (12866 2.5" = 535cfm). If I decide to go this route, I will look at the 5" round x 14" long body beside the gas tank and then see how loud it is with these mufflers. Then if it is too loud, then mount the 4x9x14's under the seat.

tried the 18 inch magnaflow ovals. Just would not fit. Went with the 14 inch.
Sound is loud, but not unbearable. May try an H pipe next.

How does the sound of the MF 4x9x14's compare to the FM40's?

An H or X pipe should bring down the sound a few decibels.

An H or X will quieten it down a little. I added an H pipe to my 4" "street" system and it made a noticeable difference. Made it sound better, more "even" sounding if you will.

I'm not a fan of X pipes. Don't like the sound at all, but they do make more power than true duals or an H pipe.

Try a couple small resonators near the tips. Worked for the factory on several models.

In my opinion, the sound of the 14 inch magnaflow is much better than the Flowmaster 40s that were on it. Much deeper tones. I believe quieter. Especially at idle. Also the Magnaflow's just look better; steel and thinner top to bottom.

It's a convertible so I am trying not to be too loud. Going to drive it a little than probably add the H pipe.