Hi Mark,

Chris and I did a fair bit of experimentation back in about '98 on quitening pipes, even tried the full 4" spiral type with no glass packing through to what Rob pic's are. I found there was the louvered tube, perf tube with large holes (4.5mm?) but less of and perf tube with say 2.5 or 3mm holes but many of. This last one was by far the most successfull. The full spiral type were a messy sound.

I ended up using exactly what Rob has pictured with the spiral washers on the 20mm tube inside the fine perf glass wrapped pipe for rego with a bit of extra steel wool. I replaced the 20mm tube with a length of booker rod and kept staggered spiral washers, but for the entire length of the pipe. I think it got it down around 100db, but mine is only a low comp 302 with 2" tube.

I figure the key was to interfere with the nose/centre of the sound wave. With straight through tube this does not happen - the front of the sound wave is free to travel right through uninterupted.

I originally tried two 15 or 18 inch round perf mufflers with a 3" chamber between them. I thought this idea would be great but was no good. Probably needed a small baffle in the centre chamber.

Rob, that is so uncanny - the pic with the tube is almost identical to mine. My washers have clearance between them and the tube, and was supported in the tube by a disc with holes at each end. Got me through rego but really choked above 3500revs.
I'm going to have to test it again as mine has been out of rego for more than 12 months and in ACT it will need to go over the 'pits' again.

The Summit cone looks interesting, when I have mine apart for rego I might try something like it.

Rob - I don't think you can delete a post

This first pic is of the different types of perf tube I was refering to. The hole sizes are actually the same at 5/32" but you will notice one has 3 or 4 times the amount of holes. This one had a very noticable difference over the one with less.
You will also see the baffle I made for rego on a 1' tube closed at the leading end - a bit rusty now. The one I run now has more spirals of a smaller overall diameter mounted on a 10mm booker rod for the full lenght of the muffler.

http://www.clubcobra.com/photopost/d...98_Medium_.JPG



This pic shows the auger style muffler which does not use any packing material at all. It is the full 4" diameter of the casing. This one is a continous spiral but some use a segmented spiral.
I found that these seemed to be noisy at idle but did not get expectedly louder at higher revs. The sound was messy like a rumbling in a tin can.


http://www.clubcobra.com/photopost/d...02_Medium_.JPG

Just wondering, I'm pretty sure I have seen a Daytona where the pipes cross over in front of the engine in the engine bay before exiting on swapped sides, has anyone done this in a Cobra, or is there insufficient space? This seems like a good way to get extra real-estate for a muffler? Not sure about under-bonnet looks however......

Ben

I am guessing that this would be Tony's Daytona. It was an interesting setup and certainly did use the space at the front of the engine well. There were some problems with keeping the engine cool and I seem to recall that he was looking to move away from this arrangement to improve the cooling. I haven't seen the car since so I am not sure what eventuated.

Geof

good point re: the heat

I have been thinking about how to turn down the noise a little, and it seems the two sytems with electric cutouts may be the way to go. Flip a switch and quiet,flip the switch and rock and roll. Now just find a way to make it work.

Has anyone ever db tested their car at ilde?
I am getting 85 DB at a distance of 7 ft.
427 11.3 to 1 compression ,solid cam

Idle speed is 1100 rpm

My LS7 is 78db at idle with the meter 45 deg 4 feet from the side pipe outlet

Prior to inserting the perforated baffles and wrapping with exhaust mat my car at idle would clear the sheds at QR in about 10 secs. At a guess in those sheds it was probabaly about 112dba but knowone would stand close enough to test it! Lol I know that at full noise at QR main straight from the flag marshalls tower it read 124dba... They said I needed to make some adjustments before I could run at Lakeside!
Spookypt

How much power would you lose if you went under the car through a muffler and then double backed through the side pipes? Sort of like a truck exhaust.
JD

You may actually be able to gain power this way. Utilising better headers than the shorty's most guy's comprimise with, and good flowing performance mufflers and back through low restriction side pipes, may not cause the losses you would assume.
BUT, most Cobra floor pans and ground clearance don't allow for a muffler to be fitted before the rear axle unless you have the car jacked up like a daily shopper, and you wouldn't want to plumb the pipes past the rear axle twice. The usual set up with under floor systems is a slim resonator (torpedo/hotdog) before the axle and main mufflers after the axle. Even fitting in the cats is an issue.

When rebuilding my side pipes, I placed a modified Harley/Davidson exhaust baffle just before the turnout. At the time, there were different models of the baffle, don't recall the specific one I used.

The mufflers are the 427 Corvette side pipe mufflers, heavily modified.

At the front end used, the Car Chemistry 3 disc exhaust inserts. Reduced the size of the hole in the center tube.

Car Chemistry Exhaust Inserts - SummitRacing.com

With the set up, significant sound reduction was the top priority, accepting in advance what ever power loss there would be. My Z06 with a Bassani X pipe and the Borla Quad Stinger Exhaust is louder during acceleration etc.