This is after the additional of the MagnaFlows. Driver side sound level. Notice that I picked up some low freq drone around 230KHz (or looked at differently, I didn't get much improvement in the sound level at that frequency after the change, but the frequencies around it did see a lot of reduction).

This is with UF only, 8 ft behind the car.

This is UF + MF, 8 ft behind car.

I should point out that the frequency response of the microphone on my wife's smart phone really falls off below 100Hz, so you need to be careful to not read too much into the really low frequency energy if you try this. I actually picked up a noticeable drone, only at idle in gear with the UF+MF. It doesn't even show on a plot, but my ear doesn't lie! As soon as I crack the throttle it goes away though.

For my Cuda, I bought my exhaust components from Accurate Exhaust Products LTD and it uses both a "Muffler" and a Resonator that look stock. Both are pretty much straight through and there is a low rumble for sure in the interior but the tone at idle and driving is very nice. I would make a recording of it, but I am not sure it would capture the sound very good. Inside the car, you can talk to a passenger at cruise but you do have to speak up a little bit.

Here is a photo of the two components together and with the E-Body I would not worry about bumps at all. The exhaust hangers in an E-Body keep the exhaust locked in pretty tight.

I also have a photo of the inside of the muffler if you are interested as it shows the very slight bend!

Dave,
I have not tried that app but I have tried a decibel app. Thank you for posting the information.

I have heard different things from different people about the loudness of the straight thru type mufflers. It does seem to matter on the size of the engine and the pipe size like you pointed out. This is why I am thinking of running two round mufflers on each pipe with the x-pipe.

My current OE 2-1/4" type mufflers (no resonators) are at least 12 years old and they are probably burnt/rusted out some over the years. They are fairly loud at idle and quiet at cruise and loud again at WOT. My phone app showed 88-91 decibels at idle from standing around the rear tires and working my way back to the bumper just above the tips. I can't imagine that the phone app is real accurate but it does give me a reference if I do swap out this exhaust this Summer.

Steve,
I have checked out the Accurate websight and I believe that those are 2-1/4" inlet/outlet with 2" tips. NOTE: The stock OE style mufflers are very restrictive (apx 175cfm). The straight thru 2.5" type are in the 500cfm range, but they are louder.

I do like their Magnum straight thru stock looking mufflers but they are a little too pricey for 2-1/4" inlet/outlet and I was told that resonators would be required with the Magnums to keep the noise down.

I am looking at a full 2.5" system from my existing TTi headers back to 2.5" tips. TTi does sell the 2.5" system all the way back and since they designed the headers, then my expectations are that the 2.5 exhaust should bolt up with little to no mounting issues. The exhaust is not my worry, it is the unknown loudness of the straight thru mufflers that I am worried about. I may have to change my plan before I purchase the parts but until then, I need to decide or find out how loud a pair of the round 6"/7" mufflers would be by themselves or with a pair of 3.5"/4" round mufflers (10-12" long max length) are with them.

Thanks for the replies.

Yes (about the Accurate Exhaust) The headpipes are 2.5 up to the resonator and they are stainless.

The Frequensee app looks pretty cool. Downloaded it and going to test it to see how it compares.

All:

I realized I posted the wrong images yesterday, and have corrected them. As I noted after adding the round mufflers by the tank I picked up some drone at idle. I actually took a third step by wrapping the UF under the floor boards, and it reduced the drone. Here is the result by the drivers side rear wheel well after the wrap. Basically I discovered that a fair amount of sound emanates from the muffler case itself, at least with the straight thru design.

Y07_A66:

Why are you considering adding round mufflers under the floor boards? If you need the extra sound reduction, wouldn't an oval give you better ground clearance, and allow a bigger volume muffler to be placed there? That would in essence mimic the factory setup, albeit with straight thru mufflers.

Steve,

I agree sound recording are not very good both at comparison and for letting someone else judge the results of a specific system. That's why I used the FrequenSee app for comparison purposes. It really helped me assess the changes in sound levels after each change, at least within the mostly flat portion of the microphone frequency response (which I would judge is about 100-12000KHz).

""Why are you considering adding round mufflers under the floor boards? If you need the extra sound reduction, wouldn't an oval give you better ground clearance, and allow a bigger volume muffler to be placed there?""

Dave,
I agree with what you are saying about the oval mufflers, but my thinking was that I would not find an oval muffler that was thin enough, so that is why I was guessing a 4" round muffler.
But, I found an oval muffler made by Magnaflow (#11226) that is 4" thick which is also a straight thru type of muffler (offset/center). I may still need to add round 6"-7" mufflers beside the tank to keep the noise down, but the oval straight thru muffler should help allot on noise reduction while keeping an open exhaust.

I may end up with a setup close to what you have, except both mufflers will be the Magnaflow's and 2.5" pipe.

Note: The above MF muffler will fit the TTi non-muffler design with one minor change. The OA length of this muffler is 2" longer than the Super Turbo part #17733 that TTi references. I would just have to cut off 2" off of the X-pipe length at the muffler end.

Ref: Dynomax: 2.5" #17733 (TTi option) 4-1/4" x 9-3/4" x 14" body. Per Dynomax: 410cfm (186hp)
Magnaflow: 2.5" #11226 4" x 9" x 14" body. Per MF: 530cfm (232hp) per muffler. (these are unrestricted numbers per the manufacturer)
2.5" exhaust pipe: 509cfm

Thanks again for your help Dave.

It appears that I will be looking at an oval and a round straight thru muffler per side. This setup will give me a 2.5" "straight thru" exhaust setup that includes a x-pipe (TTi non-muffler exhaust kit) and 2.5" stainless R/T tips (Accurate). This should be as quiet as it will get for a 2.5" straight thru exhaust setup.

Personally, I'd run some sort of mufflers ahead of the rear axle, then go up & over, then a pair of straight-throughs (6" dia. x 18" long) between the frame rail & the gas tank on an E-Body. I like the expansion chamber in a couple of places in a full exhaust like that. About the thinnest oval mufflers you will find with 2.5" internals is going to be 4-1/4" thick - pretty standard.

Y07_A66:

Not sure if you still wanted to see the axle side of the round mufflers, but here are a few. A couple of comments. Custom bend pipes allows the bends to go all the way to mating with the muffler, which helps reduce overall length. With slip-fit connections, there needs to be a few inch long straight portion for mating which makes the overall muffler length longer. There is a little over a finger width between the over-axle pipe and the shock. My mufflers are hung a little low to allow the turn down to get under the rear valence without pointing directly at the ground (which I did not want).

Closer view of pipe to muffler connection.

Clearance to gas tank.

Turn down area.

Dave,
Thank you again for your pictures. Nice job getting the 3" exhaust to work in those areas especially with the 7" muffler!!

I wanted to bring this thread back and get some more replies. I had planned on replacing my existing exhaust system this past year but other things came up. So, I am going to try and replace it this coming Winter.

I already have the TTi SB headers + 2.5" reducers. I am currently running tru-duals back to the original 6.2" diameter mufflers (18" case length, 2.25" pipe) and then thru the stock 2" R/T tips.
My plan is to remove the existing pipe, mufflers, and tips and buy the TTi 2.5" X-pipe assembly but with the Muffler Delete pipes (under the seats) that they sell. I want to add my own flavor of mufflers to the system and try to keep as wide open of an exhaust that I can. I will then buy the aftermarket SS R/T 2.5" exhaust tips.

After discussing this in detail with Magnaflow, my goal is to have a DEEP sounding exhaust at idle and at a cruise. I also want to use their 530cfm free flowing series of mufflers (Not the XL series which is a very restrictive 3 chamber design).
Note: My existing 6.25" x 18" case OE style mufflers are about 175cfm each.
I also want to keep the sound down so that I don't piss off the neighbors or the police and I want to only use rear mounted mufflers.
After searching through several muffler brands, sizes and shapes, and after many emails with the Magnaflow tech, I decided on a set of round MF mufflers that will mount in the "area" of the OE mufflers. I had a few choices of mufflers and I gave these to the tech to try and get some idea about the loudness of these mufflers. I first considered the front mounted mufflers, then I considered mounting both front and rear, and now I am leaning towards the rear mounted mufflers only. This is the reference that he gave me for noise:


""On a scale of 1 (stock) - 10 (straight pipes) I would rank the mufflers as follows (530cfm):

A) front mufflers only - 5/6 (#11226 = 4" x 9" x 14")
B) Rear mufflers only - 8 (#12866 = 5" dia. x 14")
C) Both front/rear mufflers - 2/3
D) Rear mufflers 6" dia. x 14" - 5/6 (#12616)
E) rear mufflers 6" dia. x 18" - 4/5 (#12646)
You may get a fair amount of drone with just the rear small round mufflers.""


My existing 6.25" OE mufflers are at least 13 years old and they are worn out, but no drone from idle to WOT. They are pretty darn loud at WOT. I consider them to be quiet at idle and at cruise and I think that they are too quiet. So from the above reference, I am aiming for the middle of the road for loudness and I am leaning towards the rear mounted 6" diameter x 14" long mufflers mounted beside the tank.
Once I get the TTI X-pipe, muffler delete pipes, and R/T tips installed, I will know exactly how much room I have to mount these mufflers. The OE muffler exits are offset towards the bottom, and the MF are straight through. All this means is that the MF muffler will hang down lower at the exhaust tip. But since this muffler is 6" shorter than the OE, I plan on moving the MG muffler towards the front of the car a few inches so that the muffler "may" not be seen when looking at the rear of the car. Plus if this 14" muffler is too loud, I can go for the 6" x 18" muffler and still have some room.
I am hoping that the combination of the 2.5" pipe, X-pipe, and the full length exhaust will keep the overall loudness down enough so that I don't have to buy the 18" mufflers or worse case, buy a set of oval mufflers to mount under the seats. I won't have all of my parts until mid-Winter, so I still have some time to think it through.

If anyone new has mounted their 2.5" mufflers beside the tank on their B or E bodies this past season, please feel free to give your opinions.
Thanks again to Davenc for all of the db references on his 3" system!



Thanks to all.

http://www.accurateltd.com/E-body_c_102.html

have a look there you might find exactly the mufflers you are looking for there