Sorry I don't agree. Although the freer flowing exhaust the more power will be made, and the noise will be louder, If you could generate the opposite acoustical frequency as the exhaust, the power would be the same, but the sound would be less.

I believe the Stealth (figher/bomber) uses this type of technology.

The "anti-sweeping generalization task force" :D

originally posted by Quicksilver,
"maybe I'm trying to relive my childhood?
Why relive it? It is easier to just skip that whole 'growing up' thing."

Ogden Nash wrote....
" You are only young once but you can stay immature indefinitely "

Wayne, yes this flap device would have to be pretty well engineered
or the possibility of rattles or buzzing would be huge.

Mine makes noise, therefore I must be going faster :)

"the quieter whatever muffler you put on, the more it will be causing turbulence and impeding the flow of gases out of the engine."

- No. This is a widely misunderstood area. The real issue is the superposition of the pressure and rarefaction pulses and the degree to which they can "scavenge" gases from the compustion chamber -- and at what rpm. There is no real relation between noise and power. The flow will be highly turbulent no matter what. You will get little laminar flow out of any exhaust system.

You know I think there is a way to make the 3.2 faster and quieter, but I have yet to hear of anyone doing it. That is to install the super quiet 993 exhaust into a 3.2, but it will take some fabrication. The 3.2s exhaust is almost identical the the 964 exhaust, but the 993's exhaust was responsible for freeing up like 18 hp from the 964s 3.6. The way I would do it is modify the 993 headers to mate onto the 3.2's exhaust, which has been done many times. This would provide the large diameter desired plus provide heat. On the 993s there is a crossover which mates the two sides out to a pair of cats, and from each to a pair of mufflers. What I would do is fab a crossover out of the pair of headers, and into a pair of stock 993 mufflers, exiting to a pair of dual outs (AKA 'A Quite Boom's configuration) If anything this will have even less restriction than the factory 993 exhaust, because of the elimination of the cats, but have all the flow of headers larger than a set of SSIs. And everything will be in Porsche stainless.

On the other hand, the factory Bischoff single out muffler mated to a pair of SSIs aren't really all that loud. Just a decibel or two louder than the stock 3.2 exhaust, with a somewhat different tone. Also the annoying part of modified exhausts are not the volume of noise, but the drone which often occur in specific rpms and load ranges. If you can eliminate the drone, I think many 'loud' exhaust systems are actually quite bearable. As I have tried many mufflers mated to a pair of SSIs, I think only the factory single out is 'drone free'.

If you just want a little more power out of your stock 3.2 exhaust, without more noise, just install a euro-premuffler for about 6-8 hp and be done with it.

I'm not hugely worried about the power output. Frankly I find the cost to power ratio of most of the 3.2 mods to be way out of line. To get more power out of it I am planning on increasing the bore to 100mm, increasing the rev limit to 7500 (rod bolts and valve springs), 964 cams, .5 more compression, and twin plug w/direct ignition.

Walker (the muffler company) experimented with an electronic muffler over 10 years ago. They would flip a switch and poof, instant noise reduction. Never heard anything about it again.

So...
Is the Danske considered to be the quieter stainless muffler?

I'm really appriciating the quantity of feedback here.

Wayne

Before her rebuild, the Blue Bomber ran with a cat pipe and a GHL 1in/1out. The sound was delicious, but certainly much louder than stock. I sold that rig to a Carrera 3.2 owner who likes it v. much.

Now the 'Bomber is equipped with SSI's and a Dansk 2in/1out.
As I've just recently returned the car to the road, I can say the new combo is much quieter, but still sounds authoritative. The SSI people recommended using Dansk mufflers with their product.
I think it was a good call.

As far as an "electric muffler" that's what the current boxster "sport" muffler is. It is connected to the computer and when the sensors say you are getting on it they change some baffles in the muffler to provide more noise, and possibly more power, but definitely more noise.

Electronic Mufflers
 

Saw a special on tv a while back about an experimental muffler that used electronically generated sound waves whose sine wave is 180 degrees out of phase with the exhaust to reduce noise. The amount of exhaust noise could be controlled by turning the electronics on or off. Don't laugh it worked! Unfortunately, I can't remember who was doing the muffler. I think it was a company like Flowmaster or one of the other major brand muffler manufacturers. Anyway, something to search for on the 'net.

Good Luck!

Fred Cook
'80 911SC

Other than the stock Bischoff muffler, the Dansk if probably your next best bet. Their dual out sport muffler was one of the mufflers I tried. Louder than stock at idle, a bit of drone until 2200 rpm, at which point it disappears, is pretty quiet, and then has a nice mild roar above 5000 rpm. Nice power. A single out may be a bit quieter, and down probably a couple of hp.

I have the Dansk dual in-dual out on my 80 SC and really like it, Steve is correct, rumbles at idle, little resonance off idle, and means business at high rpms. Other than that my exhuast is stock, including cat, I tried a test pipe but with that muffler but I felt like I was in high school again. I'm looking to buy a fabspeed pre-muffler and give that a shot.....any experiences?

hipo i/o boats have 'silent choice' type systems. search marine websites and you might find something better that the jc whitney cutout.
being able shut down the second outlet would be the best of both worlds.

tryan- What is a hipo i/o boat? Thanks for the lead I'll try to search that later.
I agree that the cutout would be the best solution.

sorry high performance inboard / outboard. you can switch from thru the hub ( quiet ) to out the transom ( not quiet ). diameters might be larger than what you need but search for 'silent choice' or 'captains call' . nothing sounds sweeter than a 911 on the pipe, but it would be nice not to piss off the neighbors when you have to sneak home late at night.

This is the first hit I found on the Silent Choice.
http://www.marineparts.com/partspages/Corsa-Gil/gil3.htm

Can't see how it works from the picture but there must be a way to make something like it that is smaller.

Wayne

rex marine. eddies. gil marine. i'll look in powerboat.

another thing that might work is a diesel exhaust brake.

this picture shows the y. you just need the guts.

how about a heater flapper and a cable just to test it?

Wayne,

I think you should get SSIs and a dual-inlet /single-outlet Dansk sport muffler. $hort of that, get a fabspeed "euro pre-muffler" (nice stainless thing that replaces the cat), and a single-inlet/single-outlet Dansk sport muffler. Either way, as long as you get rid of the cat and use a Dansk sport muffler, you'll get a nice little performance improvement with minimal noise. You'll still hear your fan, put it that way. And I think you'll like that OE stamped design & look of the Dansk.

Cheers,

tryan, the openings out of my muffler are 3" round. Is that a common i/o exhaust size?

Randy Webb says.. "There is no real relation between noise and power. "

I guess that's why race cars are so quiet, eh. I never meant to say that power is a direct result of noise. That's ridiculous. What I mean is that, at a certain point, noise becomes a necessary byproduct of making more power. I doubt very seriously that the setup Bruce Anderson was able to make the most power with in his tests is anywhere close to the stock brand of quiet. In fact, I bet it's a good louder than my GHL system.