Unfortunately, the 9ff consumer oriented "switchable" exhaust uses a restrictive chamber muffler, and is limited accordingly:



Interestingly (and illustrative of the limitations on their consumer system), 9ff uses an entirely different exhaust system on their very high HP cars. The following is a photo of a portion of the engine of a high HP 9ff car (sent to me by 9ff) -- you can see part of the exhaust -- notice that it bares little resemblance to the consumer oriented exhaust:



If you REALLY want to know about exhaust performance, read the following articles:

http://www.lcengineering.com/TechNotes/TechNote68.htm

"Straight Through Versus Reverse Flow Mufflers [aka Chamber Mufflers]

Having a optimally free flowing exhaust all the way from the manifold would not do much good if the restrictive stock muffler is still used. The inlet and outlet diameters of the pipe in the muffler should also be as large as feasible, so as to allow free flow of exhaust gases. A straight through muffler would be preferred to a reverse flow muffler mainly because the process of air re-direction in the reverse flow muffler is too restrictive. A straight through muffler design would allow exhaust gases to be expedited out as efficiently as possible, although the muffling abilities would not be as efficient as that of the reverse flow design. Therefore it will be inevitable that the exhaust will sound louder than before, but as mentioned before a couple of times, an aftermarket straight through muffler uses noise suppressing material that tones down the sound to that of one that's deep and throaty and not irritating. However, as will be discussed in the next section, a new generation of mufflers may be able to tackle this."

http://www.sportcompactcarweb.com/te...scc_ssbbpart2/

“To produce the most power, an exhaust should have the least amount of restriction to the exhaust flow. Restriction hampers the burned exhaust gases from exiting your engine, causing some charge dilution with the incoming fresh fuel/air mixture. (In other words, exhaust left in the cylinder is mixed with the fresh intake charge.) This causes a loss of power. With greater restriction, back pressure is generated, making the engine work harder to pump the exhaust out of the cylinders. This is one source of pumping losses.

Some stock mufflers have up to 18 psi of power-robbing backpressure. A well-designed performance exhaust typically has about 2 to 6 psi of backpressure. For comparison sake, an unmuffled straight pipe usually has 1 to 3 psi of backpressure.
To get the least amount of backpressure, most of the good, high-performance mufflers available today have what is called a straight-through design. These type of mufflers quiet the exhaust by the absorption of high frequency vibrations in a heat-resistant packing usually consisting of stainless steel mesh and heat-resistant ceramic fibers. They typically have a straight inner core with no baffling at all, much like a straight pipe with many small holes. The pipe is louvered or perforated when it passes inside the muffler's shell, allowing sound energy to pass through the holes but leaving the exhaust gas flow unimpeded. You can see straight through these types of mufflers. The louvered or perforated core is usually wrapped with either Fiberglas wadding, hence the old-school term Glass-Pack or on the better mufflers, stainless steel mesh to help further absorb the sound. On straight-through mufflers, the longer the muffler, the quieter it is. The length usually has no effect on the backpressure, just the noise output. These mufflers work in the same manner as the silencers used on guns. If a silencer impeded bullet travel, you would definitely have problems!”

http://www.geocities.com/MotorCity/7...ory.html?20052

http://www.sportcompactonly.com/catb...ent-guide.aspx

"Stock mufflers use closed designs with several internal baffles to deaden the sound. While this approach works well from an acoustic standpoint, it causes considerable backpressure and tends to degrade performance. Most aftermarket mufflers for sport compact vehicles use a straight-through design without internal baffles or chambers. Instead, they channel the exhaust flow through a perforated pipe surrounded by a sound-absorbing material, such as fiberglass."

The following is also a good analysis relating specifically to Porsche exhausts (albeit for marketing purposes):

http://www.fabspeed.com/993mufflers.html

There is simply no denying that straight through mufflers are superior to chamber mufflers from the perspective of power.

Craig

 

kudos to you Craig, you know your stuff, thanks for the info. if i didn't have Sol, i'd call you for my next exhaust advice.
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i am sorry tho, as we are talking about two different things and by the way, i agree with you. .. from my own experience, (monster boat motors) i understand the power loss with restrictive (quieter) exhausts.. . in an offshore boat, you can feel and see the rpm loss when the mufflers are switched on, especially with twin 572 cubic inch motors. ..
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the reason i brought up the 9ff exhaust is that i thought this thread was about sound. i love the fact that i can change the exhaust note on my turbo with a flip of a switch. i did not buy the exhaust for maximum horsepower, i bought it because i had the choice of quiet or louder... i love choice... at the louder setting, it isn't even that loud but sometimes i just want it quieter. my point is, as the car is only about 500 hp, i wasn't going for maximum horsepower gain. .. i have learned in life, that EVERYTHING is a tradeoff.. besides, when i REALLY want to drive fast on the street or track, i ride one of my motorcycles... which of course, i would like to design a switchable exhaust for.. good to meet you.. JR

 

JR,

It sounds like the 9ff exhaust is perfect for your application and the ability to change the volume is very cool. I am a BIG fan of 9ff products!

Craig

 

The sound of 9ff exhaust is unbelievable. OMG, it's hard to explain it. I stopped by 3T Motorsport tonight to listen to it.

 

this is a cool website..
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http://www.kreissieg-usa.com/index.php
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check out and listen to the vids..