Variable Exhaust - Sound and Flow

[Mikeyas]

The problem:
Installing a better exhaust system to free up hidden power within the restrictive stock Honda exhaust systems. But often being left with a loud and obnoxious sound 24/7. Excessive droning and noise getting on your nerves.

Solution:
Use a system to control the volume and flow of the exhaust to desired levels.

This sort of system can be found on some European cars such as some VW's, Audi's, Aston martins and some motorbikes. The idea they use is to have a stock sound level at idle and cruising speeds, but at Wide open throttle and higher rpms, valves, flaps & switches engage to create a better flowing exhaust system and hence a louder sound.

For example:
1996 BMW 328i system
http://z.about.com/d/autorepair/1/0/_/S/77996943.gif

The Audi TT 3.2 and Volkswagen R32
both have a exhaust system made for VAG by Remus Racing. The system incorporates a "flap" that restricts exhaust flow in order to keep things quiet. The flap opens after about 2500RPM (from my experience, R32 owners seem to have this much higher, at over 3000RPM). Most of the "research" I've read comes from R32 owners. Of course, the packaging in a Golf body is very different than a TT, and the flap appears to be one of those differences -- it's on the left side of the R32, and the right side of the TT.
I have begun to slowly build some ideas on a variable exhaust system with the goal of being able to reduce the exhaust noise level when required

http://www.mindspring.com/~wchou/tt/exflap_mod.html

Motorbike
http://www.mcnews.com.au/NewBikeCatalogue/2001/Suzuki/GSXRimages/GSXR1000_exup_600p.jpg

Why i have not seen a greater aftermarket support for these systems baffles me. I have found one source of useful information at

http://autospeed.drive.com.au/A_0883/cms/article.html

This idea looks promising, but upon searching for more i came up empty.

But what i would like to know is:

-Has anyone attempted a system?
-Know anymore about VariFlow Technology (Australia) - 0409 288 347
-Know of companies that create systems of this nature?
-Positives and negatives to such a system?
-Possible circumstances arising form restricting exhaust flow?
-Discussion on the idea in general.

[bennjamin]

Yes. Trucks use it ( in opposite of theory tho...they use it as an exhaust brake to SLOW the engine thus truck down)

But otherwise , its a minor thing in regards to an overall performance increase. Im sure the price outweighs the "improvement" if any.

[|N|]

just get a mugen twin loop.....

[CUL8R]

very interesting!

the only thing ive seen close to this was a guy in the US (im sure heaps of em do it) has like a Y pipe from the cat, at a certain rpm it closes the end of the exhaust and open the part where it becomes effectivly like no exhaust from the cat back. but this is best for top end turbo?
NA would suffer a fair bit.

[Mikeyas]

Yes. Trucks use it ( in opposite of theory tho...they use it as an exhaust brake to SLOW the engine thus truck down)

But otherwise , its a minor thing in regards to an overall performance increase. Im sure the price outweighs the "improvement" if any.

Are you refering to improvement in lower sound. Or performance. Because performance wise its not an issue, basically a method of using a performance increasing exhaust without constant noise.

[bennjamin]

i refer to simply performance. Noise wise , this might "Work".
Having this on a car possibly is good for low to mid range due to giving better back preassure ~ and then opens up with throttle for top end goodness.

[saxman]

do a search on google for e cutout
this concept is something that's been done for years, and there are several products on the market available

[Mikeyas]

ahh thanks, interesting idea.
http://www.superstang.com/powered_exhaust.htm
But looks like it would be very loud. Dump the exhuast just before the rear muffler.... would this not also cause issues with exhaust getting trapped under the car? Hence the tip extending past any of the rear panels?

Good to see the things people come up with out there. Any other brands you know about?
because searching for them is not as easy as it sounds.

[aaronng]

BMW's X5 uses this system as well.

Most gains from muffler depend more on the piping between the engine and muffler. Even if you have the best super high-flow zero noise muffler, if you have restrictive headers, cat or piping, you won't see much gains.

[Mikeyas]

well the focus is not on gaining more power.......
But having the ability to tone down the volume on a system which has gained more power when required...

[dsp26]

i posted this in another thread:
http://www.gccorp.com.au/automotive/product_info.php?products_id=216

however your idea (based on the diagram) with TPS sensor control would be an interesting addition.

there is one other design i've seen which actually gives a performance gain, the flap either diverts to the catback or to the ground (meaning open header) which is actually for track use. this was also in the states so i'll have to dig up the article.

[Mikeyas]

Thanks for that link. It finally gave me the ammunition to start a good search. Found some good information and some good links. found an Apexi design which looks good and also in a manual format so i dont have to rely on electronics working or failing.

[TheSaint]

please share your found information and links with us when u end your quest