New cat-back exhaust system

[blkfordsedan]

Just installed a new 2-1/2" manderal bent cat-back exhaust on my stock 04 Mustang GT.
It's made by Pypes and is 304SS all polished to a mirror finish with "Violator Rude-Sound"
mufflers and 3-1/2" polished SS tips! It fit well, looks incredible and sounds awesome......
One thing is rather odd: At approx 2250rpm and again at 3300rpm it hits what I can only describe as a "musical resonance". Just like when you blow across the top of an empty beer bottle (we've all done that) or when you wet your fingertip and run it around the rim of a crystal wine glass and it "sings". It plays a very loud A-flat (I'm a drummer so I have no sense of pitch. Bass players will also understand this handicap) LOL. My only guess is it's a combination between the volume and pressure pulses of exhaust gas flowing out the tips and the diameter, thickness and T304SS material of the tips (possibly even the tip length). When I get time I'm going to adjust the clamp-on tips fore and aft or maybe even cover part of the tip opening with aluminum duct tape to see if the tone changes.
Has anyone else experienced anything similar?
Oh Yeah- It is considerably quieter at highway cruising than the factory exhaust, no drone effect, and seems to have added a slight but noticeable increase in power.

[bhazard]

Are the mufflers chambered, 'pathed', or straight-thru?

[blkfordsedan]

Not sure what pathed means, but they are not chambered and there are no deflectors or anything like a Edelbrock. They look like an oval turbo muffler with center inlet and offset outlet. When you look inside they are basically straight through like a cherry bomb, louvered tube with fiberglass packing, except there is the slight internal bend to line up the inlet and outlet. Even with the slight offset bend, you could almost push a pop can through in unscathed.

[festivaWES]

airflow follows a path---pathed

[solatare]

most straight thru muffler designs ive tried have had that wierd resonance issue, and unfortunatly for me, its worst at 3 to 3500 rpm, where my little 4 cyl cars run at speed on the highway, ive found that adding a second shorter muffler, like the 4 inch race ones magnaflow makes, help alot, sometimes eliminating the drone, a resonated cat also worked well for me. also lovered designs are horribly restrictive, and chambered designs are a bad idea for turbo cars since you lose the pulses they work from as the exhaust passes thru the turbo, sport compact car and hot rod have both done tests on this, some of the article might still be on scc's website, but with the total change in editing staff there im not sure, havent checked cause i dont like the way its written now, stopped reading it. oh, and one other odd property of a magnaflow muffler or other straight thru, acoustic damping muffler, they get louder as they get hotter, so after a couple hours on the highway or a few minutes of aggresive driving youll see more exhaust noise, muffler length also plays a part in where this resonance, or drone, comes in, my subaru has a y and 2 straight thru design mufflers, both are about 30 inches long, and another round one after the third cat, no resonance in the car, but after driving for an hour i get more noise from the exhaust, my festiva has a resonated cat and a 20(?)ish long muffler on it, longest one i could get to fit where the stock one was, and its very quiet till i hit a hill, then it gets almost painfully loud.
im also going to play with moving the muffler and maybe adding another one to get it quieter overall

[bhazard]

Pathed meaning like a turbo muffler (cherry bomb turbo or dynomax superturbo) where the muffler has an S shaped tube inside the exhaust runs through. They flow better than chambered but not nearly as good as straight through.

[blkfordsedan]

I wouldn't really call the sound a typical drone. The factory turbo style mufflers had a very noticeable drone at highway speeds. The dull, obnoxious sound you typically get with glass packs (especially when they exit under the car) is a function of the sound vibration (wave length) matching the actual length of the car which causes the whole car to resonate, making you to feel like you are inside the muffler. Same principal as that video of the bridge swinging and collapsing. This is different - a very sweet and clear sound, almost like a flute or trumpet. It is independent of the car with no vibrations. It sounds like someone is literally blowing a low note on a trumpet into a piece of pipe. The new system is indeed louder than factory on the outside but actually quieter in the car at cruising speed. It is not annoying or bothersome at all.........just kinda odd and cool.