Jordan... Not sure this will be of much help but I have been trying to make my car quieter and get better sound quality for some time now.

I have a DynoMax bullet where the OR pipe used to be and that runs through a 3" i-pipe and out a flowmaster cross flow (one day that will be gone too).

The interior resonance dropped by nearly 50% and the exterior tone lowered in frequency. The exterior note is now roughly 25% less.

Now...I also have a cutout and open it once and while on the street (with a turndown) and at the track. The turndown is made from a 3" mandrel bend (used from a friends old turbo intake duct work) and uses a 3-bolt collector flange. Adding the turndown made a noticeable decrease in exterior sound levels. The cutout is on the i-pipe just before the rear axle bend. The interior noise at cruise or moderate throttle is quiet enough that my 2-yr-old son has fallen asleep in the car several times with the exhaust 'open'. At WOT the interior resonance is quite noticeable, but it's significantly less than our other car with long-tubes, h-pipe, and dual bullets dumped before the rear axle. I run SLP 1 3/4 mid-lengths on mine and I welded the bullet in as close to the i-pipe connector as I could so that it would be as far downstream from the y-pipe as possible.

This may not translate to what you are doing with your turbo setup, but it might give you a real-world example of what I found to work. I went through a few different configurations to get where this is now including running a couple different hi-flow cats. I get many compliments about how my car sounds and how quiet it is at low-rpm and idle. One friend (turbo mustang buddy) despises the flowmaster sound and actually had no idea I had one on my car.

My next step is to replace the crossflow flowmaster with an Ultraflow.

Hope you get it worked out.

Fred.....whatever happened to Goerge Baxter anyway...? Never see him post anymore and I've not heard any news on his car. I know the LT1 was supposedly sold and he was converting to a Dart block to run the car in Xtreme Street.

 

I had to think about this, but I've never heard this concern mentioned in development. Theoretically, I suppose there would be a difference, but practically, I doubt you could measure it. Besides, we're talking about basically straight-through silencers where added restriction would be amost non-existent. The diameter would be the same as the pipes into which they are welded. Also, flow and acoustics are different things. Sometimes people forget that mufflers deal with the sound waves, while conducting the gases. You deal with both issues differently in the same silencer. The diameter of the pass tubes generally deal with the flow, while the volume and configuration of the body, tubes, baffles, packing, etc. deal with the acoustics. There is some relationship between the two (obviously), but that's it in a simplified form.

 

Heh, I played with that on a 3rd gen that had a custom dual cat y-pipe (cats right before a flowmaster y which was part of the intermediate pipe) and found that putting a crossover as close to the collectors as I could (probably3-4” from the passenger side collector and 10” or so from the driver’s side collector) not only significantly quieted/mellowed the setup, but also showed an improvement at the track with no other changes (with and without the cats installed).

WRT to positioning, the closer to the engine you get the more sound reduction you get and you also get significantly more restriction (more then the increased sound reduction). I’ve played with this on a ford with dual exhausts and found that to run the same times as with 2.5” mufflers in the back, we had to use 3.5” mufflers in the front with turndowns (ultraflow welded mufflers in both cases). The weird thing was that with turndowns and bigger mufflers that car wasn’t significantly louder then it was with the full exhaust, but there was a bass frequency that we gained that made the floor and even the ground around the car shake at idle, that went away when the car was moving. I suspect that that could be gotten rid of by angling the turn downs some, but we haven’t played with it (it’s kinda cool and not annoying when driving it) Typically, if your f-body is happy with a 3” straight through in the stock location, you’re probably looking at a 3.5 or maybe even 4” where the cats are.

 

The closer you can get to equal lengths from the header collectors to the y collector (or h or x pipe), the better it will sound. Odd firing frequencies are canceled out with equal length downpipes. If you got to a difference of 6", I'm not surprised you saw a difference.

 

George is still working on the 30th SS convertible. He had a Dart Iron Eagle, Brodix heads, a MoTeC injection setup, etc. The engine made over 1,300HP on the engine dyno, and it now in the car. He is hoping to get as much as 500# out of the car, and we are part way there.

The cost of doing all this has been staggering, and that is a problem at this time. He is also discouraged because he thought if he could run under 8.5 and over 160mph he would have a chance. But now the big guys are getting in and are running well under 8.5.... so, he put the wheelie bars on it, and it probably just going to run F-Body events for a while to see how it runs.

There are some pictures of the current version of the car on the very bottom this page:

http://cjcfo.fbody.com/members/injun...l.com/PhotosF/

An interesting point on muffler testing... I know George did quite a bit of work to find a good collector muffler, and found differences of as much as 30HP among different designs. I think he was at the point where he was looking at 5" mufflers..... .

 

Jordon I am running two Muff's in series. Car is fairly quiet unless you go WOT. even then it is not to bad.

On the dyno it only cost me 4hp and 6tq for the second muffler. That is worth it to me.

We have tried the cones and every other supposed race type insert with no real luck on quieting them down.

I am at present running a Dynomax 4inch bullit before my SLP Dual Dual. I have a cut out right after the bullit for racing(I still pass as street legal). The bullit is loud by it self but MUCH quieter then with out it

My boss could not believe how much sound that pretty much hollow 4 inch tube could kill.

Good luck man!