Agreed with Ed. That crossover muffler needs to have inlets and outlets on the same side of the muffler

Even when the other muffler has been used with parallel flow paths, guys have blown out mufflers. They needed to use the welded muffler to keep the casing from breaking.

http://forums.pelicanparts.com/porsche-911-technical-forum/387071-obx-headers-2.html#post4240041

I think two separate bullet-style cylindrical mufflers laid on top of each other are the way to go in order to avoid any internal interference?. But then you lose any crossover/mixing effect. I had a nicely fabricated set of MODE headers that I stupidly sold. They also made a really nice “quiet track” muffler with a big Borla can and man was it quiet compared to the straight pipes

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/731962-racing-headers-muffler-any-track.html

This muffler was definately designed to have both inlets and outlets on the same side. But I don't think that it is destroyed.. the opening on the right where the 2 pipes are not fully welded, is where some of the packing got sucked out.

This is a bit of an experiment; I have had the pipes welded and the cover put back on.. will attempt to get it back on the car tonight after work.

I've had the same experience. Have a 3.8 with BB headers and BB 2in/2 out muffler. Without one side capped it was incredibly loud AND droned badly. Moved to Magnaflow and felt the same power and quieter but it didn't last long. 9 months later and it's much louder and more drone.

The very first post in this thread seems to indicate that keeping the banks separate (no cross over) may benefit above 3000RPMs.

In that post it's interesting how much torque was gained when you ran with no muffler and thus no exhaust cross over.

Would be very interesting to see what the results would be with megaphones or simply two small muffler on each side. Something like these:
Race/Track | M&K Exhaust

The description on that M&K page should say:

NOTE: These mufflers whistle at idle and may cause operator laughter and/or may cause your friends at the track to poke fun at you........... :D

Kevin,

Or two of these and keep banks separate:
Ultra Flo™ Welded Round - Centered / Centered Muffler - P/N: 17230 - DynoMax® Performance Exhaust

Sorry to prompt you to post an alternative Sal. I was just giving the M&K guys a little jab with that.

They do sound pretty good when you crank up the rpms. I had them on my former '87 Carrera for a while and they are very nicely made.

https://www.youtube.com/watch?v=--Br8BWBTmE

The GT3 muffler is interesting to study and provides some ideas for what the factory did, see these pics:

http://forums.pelicanparts.com/uploa...1550518268.jpg

http://forums.pelicanparts.com/uploa...1550518268.jpg

http://forums.pelicanparts.com/uploa...1550518268.jpg

Yes the track mufflers do have an interesting whistle at low rpm. Idea behind them was that if you add a short secondary to headers it will fatten up the torque curve. They do just enough sound dampening to take the edge off open headers.

Remember the GT3 back box is a 3rd muffler in that system. Most of the sound deadening is in the primary mufflers. Running the back box alone has to be pretty loud, even using the "quiet" path. We are working on an active exhaust right now that uses two pre-mufflers and one back box that is partially bypassed when the valves open. Cats can be fitted in place of pre-mufflers for a green option.

Brian,
What I found interesting with the GT3 exhaust is that in bypass mode (all 3 mufflers in bypass) the system acts like 2 separate exhaust banks right to the tail pipe. Then a small 'U' connector at the 2 outlets of the final can. I was just observing the fact that the factory GT3 exhaust separates the banks at hi-loads.

Basically, with all 3 valves open on all 3 of the GT3 mufflers the headers, for the most part, go straight out to the exhaust tips via straight piping. All 3 mufflers are by-passed and the banks are kept separated.

One more cut away of the other 2 side mufflers that are tucked in the rear fenders:

http://forums.pelicanparts.com/uploa...1550526977.jpg

Well, after getting the insides welded up a bit, I had it closed up and run on the dyno again.
https://i.imgur.com/Y7F4LBn.jpg

the top line is the headers and open pipes.
Middle line is the Dynomax 17552.
Bottom line is the M&K with fully open tips.

This is as far as I am prepared to go with the Dynomax 17552. I don't think there is any point pursuing it further. My next muffler will be the Dynomax 17231. I think "Tippy" and Mike Bruns ran it on their 3.6 and found it to be only a handful HP lower than their open pipes. (but had different headers).

I like the idea of those 2 Dynomax 17230 as well. Would you run them straight out the back? Or is there a benefit to having the extra bends in the pipe to route them across the rear of the engine, and have the left back exit on the right side of the car and vice versa?

https://i.imgur.com/vPrLvXl.png

Also, with my 3.0 engine, with my 10.2 pistons, itbs, webcams and euro headers, (1 & 5/8ths) should I be aiming to use 2.25inch, 2.5 inch, or larger pipes?

Thanks for doing all this work. It looks like the low rpm torque is just the effect of getting on the throttle. Right?

Correct!

I'm not sure the single 17230 cans will fit directly onto the header and out the back? I think they are near 24" long.
I suggest tucking them both one above the other behind the bumper then the out the opposite sides. But for test purpose I don't think it will matter much how you route them. If you can mock them up straight shot and dyno that would be a decent test. I suspect your WOT pull numbers will improve with straight out and no cross over.

I have a decent exhaust software calculator called PipeMax and for a 3.2L with peak torque point set at 5800RPMs it comes up with these specs:

Primary pipes at 1 5/8" OD (1 1/2" ID)
Primary length at 29-31"
Use a true TRI collector with a well formed spear tip inside.

Secondary pipe at 2 1/2" and a length of 20" if possible. The length of the secondary is not as important as the primary lengths. The secondary length is the optimal amount of pipe from the collector output to the muffler in point.

If you compare what pipemax comes up with it's a lot like a set of factory RSR headers into a 2in1out factory muffler. Only thing slightly different is the size of the secondary pipe. Factory is around 2" and pipemax calls for 2.5"

This is a factory headers setup and those are around 29" primaries.
Like these:
Porsche 911 (64-73) Exhaust – TT Exhausts

I suspect this exhaust would produce good WOT HP numbers:
https://www.youtube.com/watch?time_continue=35&v=a-C_PJn72Xc

From these guys:
Porsche 911 European Racing Headers for 911 2.7 - 3.2 Liter Motors with Street Adaptor Part# 911-158/SA

This has mufflers right after the headers and then keeps the 2 side separate to the tail pipe. Not sure how long those primaries are but they would need to be 29-31" and 1 5/8" diam.

HI Sal
My motor is 3.0.. but yes, I have the headers from that company and they are 1 5/8ths.
I thought about getting their stinger system, but not sure how loud it would be for the street. How large do you think the pipes in that video are, after the mufflers?

I know quite a few racers who run that exhaust on 3.2’s, it’s extremely loud. One friend said he would happily trade me the pair of Flowmasters on my car for his stinger system. No way it’ll pass sound at track like Road Atlanta or Limerock.