3" catback exhaust upgrade. Surface treatment questions.

[Charlie207]

2nd startup for curing process.

https://imgur.com/a/vB47OkB

 

[Tonyrodz]

2nd startup for curing process.

https://imgur.com/a/vB47OkB

Sounds good.

 

[iamdub]

Can you explain the "piece of pipe" used to cancel the drone wavelength?

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:

Drone Calculator

Web Site Builder Description

super-null.com

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:

 

[Charlie207]

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.

 

[Charlie207]

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]

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.

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]

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.

 

[Charlie207]

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.

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.

 

[Charlie207]

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]

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.

I wouldn't be upset.