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Charlie207
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2nd startup for curing process.
3" catback exhaust upgrade. Surface treatment questions.
- Thread starter Charlie207
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Tonyrodz
Resident Resident
Sounds good.
iamdub
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It's a quarter wave resonator, which is basically what the factory resonator near the exhaust exit is. It reflects the sound wave, but a 1/4 of it's actual size and 180° out of phase, back onto itself, cancelling it out. The easiest rendition of this is a J-pipe that extends off of the main exhaust pipe, curves 90° and runs parallel with the main exhaust pipe. The end is capped off. Ideally, it would be a straight pipe, perpendicular to the main pipe. But, there's not much space to do this so the one curve is often used. The factory resonator is like a pipe rolled over onto itself. We're not gonna get into the math for that.
Here's a helpful calculator:
You need to determine the temperature of the exhaust where you will place the resonator since temperature affects the speed of sound. Since you will be cutting a hole to weld the J-pipe over, you can drill a tiny hole and insert a temperature probe. Look up the speed of sound at that measured temperature and enter that speed into the calculator. Enter in the RPM at which you experience the worst of the drone and click "Submit". You'll get the measurement for the length of pipe you need.
Here's a Google'd pic of a really clean example:
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Charlie207
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Yeah, that makes perfect sense... thanks for sharing.
I was able to take it out for a 30 minute drive last night (final part of the paint-curing process), and there wasn't a lot of drone, surprisingly. I can hear the the exhaust noise, but not that resonance that feels like a tuning fork pressed up against your skull.
The factory exhaust on the 4.4 liter V8 E39 BMWs I've owned had one of those dead-end resonance killers. They were called "scuba-tanks".
The left muffler is the real one, and the one on the right closed. And, you can't see it in this photo, but there is a weighted dampener attached to the pipe to reduce vibration. In OEM form, they are incredibly smooth V8s, and very quiet. I cut off the muffler like in this picture and extended the pipe with a long turndown. It let the V8 roar, but not annoyingly so.
I was able to take it out for a 30 minute drive last night (final part of the paint-curing process), and there wasn't a lot of drone, surprisingly. I can hear the the exhaust noise, but not that resonance that feels like a tuning fork pressed up against your skull.
The factory exhaust on the 4.4 liter V8 E39 BMWs I've owned had one of those dead-end resonance killers. They were called "scuba-tanks".
The left muffler is the real one, and the one on the right closed. And, you can't see it in this photo, but there is a weighted dampener attached to the pipe to reduce vibration. In OEM form, they are incredibly smooth V8s, and very quiet. I cut off the muffler like in this picture and extended the pipe with a long turndown. It let the V8 roar, but not annoyingly so.
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Charlie207
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Since I'm not so much a fan of the size, shape, and angle of the exhaust tip that came with the kit, I'm just leaving it off until I find something more subtle, like a basic turn-down.
iamdub
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I drive a lot for work so I check out car's exhaust tips and take notes. I liked the size, shape and angles of those on a Saturn Outlook the most, so I found one at the salvage yard and cut off the tips. Factory tips are usually good quality and, from a salvage yard, are often really cheap. At that yard, they're rang up as "exterior trim- medium". I got both sides (dual exits) for around $6 and used the RH side:
EddieC
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If a magnet sticks to the metal then it will rust. Gas grill makers get away with that misconception quite a bit.
There are many different grades of stainless steel and the word "stainless" can be misleading. I have a 1/2" thick book that I needed to read to spec the proper series material for a construction job near the coast.
Something you might want to look into is CRC Zinc-It. It is a cold galvanizing spray.
There are many different grades of stainless steel and the word "stainless" can be misleading. I have a 1/2" thick book that I needed to read to spec the proper series material for a construction job near the coast.
Something you might want to look into is CRC Zinc-It. It is a cold galvanizing spray.
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Charlie207
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Well, since it's already mounted up under the truck, and everything has been primed/painted, I'll have to wait until next time.
I suspect the T-409 that it's listed as being made of isn't super corrosion-resistant, but by the time it rots through I will have sold this vehicle off.
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Charlie207
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As an aside, after staring at a bunch of pictures and muffler cutaway images, I'm assuming that my $300 system is a knock-off of the MBRP $500 system.
Tonyrodz
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I wouldn't be upset.
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Charlie207
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Small update:
I had my truck up on a lift to be Fluid Film undercoated (mmmm.... sheep skin oil) and was curious to see how the primer & paint was holding up.
It seems to be doing well so far: no hot spots, bubbles, or rusty discolorations yet.
The 3" Kooks turndown I added to the tailpipe (the included tip looked gross, IMO) seems to have helped redirect the sound enough to lower the noise levels inside the cab slightly, which is nice.
I had my truck up on a lift to be Fluid Film undercoated (mmmm.... sheep skin oil) and was curious to see how the primer & paint was holding up.
It seems to be doing well so far: no hot spots, bubbles, or rusty discolorations yet.
The 3" Kooks turndown I added to the tailpipe (the included tip looked gross, IMO) seems to have helped redirect the sound enough to lower the noise levels inside the cab slightly, which is nice.
How you liking the new flaps so far?
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Charlie207
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They seem to be holding up well, and are doing all the things mudflaps do.
My only issue (self-inflicted) is I need to do some more trimming on the inside of the front guards. The still rub at right before full-lock.
I wish there was a version for the leading edge of the wheel well, to prevent all the spray thrown forward by the rear tires.
thingraylinetah
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I had ap xcelerator turbo mufflers on my subaru forester.
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Charlie207
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Now that I've had my catback on for a while the tone has mellowed a tiny bit, and it's been pretty good. The 30 layers of high-temp primer and paint have mostly held up, but I assume it'll get wrecked by all the salt & brine they layer on the roads.
thingraylinetah
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Vht makes high temp clear.
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Charlie207
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I actually just ordered this. It arrived yesterday, and some quick tape measuring has it at 28" OAL, so I'll have to cut 2" (1" on each side maybe) off of the existing pipes so this longer (26" OAL current muffler) one will fit.
I didn't mind the noise at all, but the rear seat occupants said it was droning enough that I'd rather quiet it down that make the kids lives unpleasant.
It's a still a straight-through muffler, so it should bark fine at WOT.
iamdub
Full Access Member
Nice! Better than having to add pipe.
I never had any complaints with mine, even on 14+ hour road trips, back when I had the 18" body on mine. That 2579 has a 22" body, so it's like the Magnaflow version known to be "like stock, but with extra".
I think so. And it'll get slightly more aggressive aver time.
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Charlie207
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I rode in the back while the my GF drove around, up hills, fast, and all that, and it actually drones pretty bad. The resonance cancels out certain frequencies when you talk. I feel bad that the kids were back there getting their central nervous system rearranged.
It weird how in the driver's seat it very minor, but just 3 feet back it's like being in a completely different vehicle. I wonder what sitting in the 3rd row would be like if I had a 3rd row seat.
iamdub
Full Access Member
If the new muffler drones, and I doubt it would as I never had a problem with mine, you could add a 1/4 wave resonator ("Helmholtz chamber") to kill the drone and be done with it.
Acoustics are a fascinating science! I learned Sunday night just how much location can affect sound perception. That 10" sub on 500+ watts would be working it's ass off but wasn't any louder than the Bose sub inside the center console. Moved it to the cargo hold and it now it slams the front seat area.
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