The Project Pad

So after installing a resonator to the 3 inch on my 5k and after it did almost nothing to the drone I'm really trying to figure out what I can do to get rid of the drone that doesn't want to go away.
Something I've been thinking about for a while includes an E-cut out.
Comes out of the downpipe and splits into dual 2.5" one side has a close off valve (E cut out) with 2 mufflers and a dual in dual out muffler on one side and then the side with the cut out has only the other side of the dual in dual out muffler.

Opinion on that? Nice and quiet for daily driving and still flow okay, open the cut out and you have the nice loud deep side and some better flow.

I believe Jim has a somewhat similar setup? but splits to two 2.5" then back to single 3" from what I remember.

Worth it?
Second idea was just run dual 2.5" without a cut out on 2 mufflers. Pretty dang simple. I'm tired of 3" and the drone that 3" brings along with it.

Just had a crazy long day at work so hopefully that makes some sense.

I've been thinking about using a 07k Rsc (apr) helmholtz resonator/s on a ur20vt. Not cheap but could be worth it.

I love my setup with the dump valve, no drone, quite on normal driving, but demonic on boost. I rode in derek's car with dual 2.5" open exhaust, and it did not drone at all. I would try dual 2.5 if a dump valve is too complex. I like the dump valve because I also run a cat on the side that goes to the rear of the car. This way I don't stink every time I drive the car, and I don't melt the cat or choke the exhaust on high boost.

Jim, you didn't have the dump valve setup last BBQ did you?

Nope, new this year.

Mcstiff wrote:I've been thinking about using a 07k Rsc (apr) helmholtz resonator/s on a ur20vt. Not cheap but could be worth it.

A helmholtz resonator has a very narrow fixed (for the most part) effective bandwidth and would need to be tuned for an individual car model (engine and exhaust layout). Taking one that's designed for a completely different setup (or "drone frequency") will do absolutely nothing for a car that drones at a different frequency. APR's "patented" technology is just a marketing ploy. They aren't doing anything different than any other chambered muffler on the market. They are all helmholtz resonators. APR hasn't created something new with this "reflected sound cancellation" aka destructive wave interference. But, I'm just an acoustical engineer so surely APR knows something I don't...

Someday, I would like to start a "truly custom" exhaust company. Take a baseline sound clip of your current car, and filter it to an owner's exact desires (within reality or the realm of physics; you won't make your I4 sound like a flat crank V12). Then design and build the muffler to meet the specs. Wouldn't be hard to model and via psychoacoustics demo what your engine will sound like prior to the build to fine tune everything.

alxdgr8 wrote:

Mcstiff wrote:I've been thinking about using a 07k Rsc (apr) helmholtz resonator/s on a ur20vt. Not cheap but could be worth it.

A helmholtz resonator has a very narrow fixed (for the most part) effective bandwidth and would need to be tuned for an individual car model (engine and exhaust layout). Taking one that's designed for a completely different setup (or "drone frequency") will do absolutely nothing for a car that drones at a different frequency. APR's "patented" technology is just a marketing ploy. They aren't doing anything different than any other chambered muffler on the market. They are all helmholtz resonators. APR hasn't created something new with this "reflected sound cancellation" aka destructive wave interference. But, I'm just an acoustical engineer so surely APR knows something I don't...

Someday, I would like to start a "truly custom" exhaust company. Take a baseline sound clip of your current car, and filter it to an owner's exact desires (within reality or the realm of physics; you won't make your I4 sound like a flat crank V12). Then design and build the muffler to meet the specs. Wouldn't be hard to model and via psychoacoustics demo what your engine will sound like prior to the build to fine tune everything.

APR just licenses form Corsa.

So do you think they actually change the internal charistics per engine?

The 'vette resonator off to the side is cool packaging:

http://www.corsaperformance.com/images/gen_banner_technology.jpg

And IMO the TTRS sounds good:

[youtube]http://www.youtube.com/watch?feature=player_embedded&v=iacH56BIR08[/youtube]

Mcstiff wrote:APR just licenses form Corsa.

So do you think they actually change the internal charistics per engine?

The 'vette resonator off to the side is cool packaging:

http://www.corsaperformance.com/images/gen_banner_technology.jpg

And IMO the TTRS sounds good:

[youtube]http://www.youtube.com/watch?feature=player_embedded&v=iacH56BIR08[/youtube]

If they are really cancelling drone the way they are advertising, then they would have to. The drone resonance frequency depends on the engine and the entire exhaust system. Even with the same engine in a different platform, the drone could differ by several hertz and you 20dB noise reduction could shrink to nothing.

Actually looking through Corsa's patent, it looks like they are using the principle of a 1/4 wave resonator which has an even narrower bandwidth than a helmholtz (but gives you smaller packaging). Therefor it's even more critical that they design it exactly for the each car. In their patent drawings, it looks like they could effectively fit 3-4 different resonators in a muffler. You could design them so they overlap to help broaden your bandwith, but it still wouldn't be wide enough to allow you to make a universal drone elimination muffler that works on any car or engine.

I did see a presentation at an acoustics conference last year that used active sound control for noise reduction in a muffler. That would be cool to do, but much harder since you need to design a loudspeaker/piston that can withstand the extremes of an exhaust pipe and have feedback sensors installed into the pipe.

Restrictor in the tip will cut the drone down a LOT without affecting flow very much (if at all) because the exhaust gases are much cooler and denser there.

I used to use a 1 7/8" restrictor in the 2 1/2" piping on an RX-7 with no measurable power loss. Have one in the Quantum right now, too. MASSIVE improvements in drone reduction/elimination.