That's my question. Has anybody done it and if you did what were the mufflers of choice?
I'm trying to get at least 800 cfm of muffler flow and doing that with a single muffler puts you into race muffler territory (a.k.a. loud).
There are plenty of mufflers out there that when placed side by side take up about the same amount of real estate as a single case but I've never seen an installation.
The idea is to use the single 3" cat back intermediate pipe and split it after the axle into a pair of bullet (or whatever)style mufflers.
Anyone?

 

What power level are you at??
I assume 400ish.......
A single 3inch Hooker MaxFlow should be more than adequate........... Quiet at idle and cruise.........
Hell if you are worried about flow step up to a 4inch system.......
Whatever you do avoid a crosflow type muffler like the plague..........

http://www.oldspower.com/vb/showthread.php?t=53999
That thread has a lot of good muffler to HP info

 

400 more less yes.
2.2 cfm per hp is what's needed before power is reduced due to backpressure. Now approaching that flow rating will see diminishing returns that's true by why leave anything on the table when it's come time for change?
My thinking really is that cutouts at the appropriate collector length will provide optimum results when I'm racing but I like the idea of open header power with the quietness of a muffled system. I know I can't get that without exhaust termination boxes of the appropriate size but I can make gains nonetheless.
A 4" catback and a high flow muffler is what I'm after. Since I've posted the original question I've gone back through my research and found a few reasonable mufflers that have great flow (1000 cfm). The Walker/Magnaflow SS Ultra seems a likely candidate. That may eliminate the two muffler debate but what I don't know is the sound quality.

 

The magnaflow has a great sound.......
Personaly I dont need or want a stainless setup as im in Alabama and aluminized will live for damn near ever.............I see you are MUCH more north of me.......stainless would prolly do you VERY well
The MaxFlow and Magnaflow have a very similar sound..........quiet growl at idle and VERY vocal at WOT without the drone at cruise.............those that truely know what power sounds like dont need to hear all that f#@$ing noise from a chokemaster or glasspack.
Over the years I have been involed with SEVERAL sub 11sec cars............ALL of which had FULL exhaust systems..............there is no "need" for open exhaust for performance...........just do some research and design a good system from the start...........

 

Where at in Alabama r u located ? I'm in muscle shoals .. Northwest corner of the state ... B cool to get a third/fourth gen cruise/group started ... Ain't a whole lot to do in Alabama lol ... N I'm seeing less n less third gens on the road n the ones I do c are usually beaters

91' bird 305 TBI T-5, trick flow 175 cc heads, 4.10 gears, lots of suspension upgrades. 24mpg @ 2500rpm hwy. 8.80@ 84mph 1/8th on street tires... 8.000's soon

 

Just outside Birmingham.........in Hoover
You are correct.......not much around that area........lol

 

This car never sees the winter so the stainless doesn't matter to me either. I'm only interested in what's available. If it's stainless, I'm ok with that. Aluminiuzed steel? I'm ok with that too.


With cars other than a 3rd gen, and a lowered one at that, the options aren't that numerous no matter how much research is done.
The idea is develop an exhaust system that performs as well as a properly tuned open exhaust. Your sub 11 second cars may have achieved that, or nearly that. I've recently been involved in a 67 A-body with a LSX454 and with all the room under that car, a full 3" dual exhaust with properly spec'd mufflers and tail pipes was easy. Trying to do that under my 86 Camaro isn't.

 

Amen to the lack of room............
it can be done tho.......even if it means a 3.5 single system...........which should be more than adequite for your needs.........and leave a little room to grow........

 

I'm in agreement. I can't imagine building too much on top of what I've got now. Low 12's are fine with me although I've yet to get there. That's why I'm researching the last few bits of the puzzle and the exhaust is at the top of the list.
These days, performance notwithsatnding, I'm heavily into tuning for fuel economy as well. Old school carbed application getting 23 highway mpg (Imperial)/19 mpg (US gallon) has it's own rewards. Last road trip netted those numbers and there's more to tune particularly on the ignition timing side. Hell, I may be able to tune this thing to run on regular octane fuel too although the iron heads tend to get in the way of that happening. Considering that the ultra lean cruise mixture I'm looking for and nearly 50 degrees of advance, I like to have the insurance that the extra octane points deliver.
Have to have the exhaust to do that too.

 

Seems like you might have moved on to other options from your original post, but I'll chime in with my setup anyhow, just in case. I've got full true duals in 2.25" following the stock routing, no cats, back to a pair of 21" long glasspacks. The glasspacks are mounted sideways in the stock muffler location, keeping the stock dual exit locations as well.

 

I'm interested in ANY way to remove the single cork of a muffler I currently using. I've seen the true dual arrngement down the trans tunnel and may go that route.
The twin mufflers are exactly what I'm talking about installed as you've described. Not sure if the glasspacks would be quiet enough for my tastes. That's assuming the glasspacks are what I think they are.
Any pictures would be appreciated.

 

Here are the only 2 pics I have right now of the glasspacks. These were taken while installing the exhaust, and only one glasspack was installed at the time. You can see where the exit pipe routes out from the glasspack to under the rear bumper. The cutoff pipe in the pic beside the glasspack eventually got a 180* U bend welded and then the other glasspack was welded to the U bend to mount the second glasspack between the one in the pic and the rear axle. It routes through another 90* bend and out under the rear bumper, same as the one in the first pic.

The second pic is just to show how much room is still available to mount the second glasspack. I had plenty of room to mount the 2 glasspacks and the straight piece of 2.25" pipe all beside each other under the rear of the car.

Glasspacks aren't the quietest mufflers out there, they are generally just quiet enough to keep a car legal under the noise regulations in most areas. Mine aren't too bad when driving the car, even on the highway. None of my neighbors have complained yet of the noise, although you definitely know when I start the engine. If you search my TGO username on Youtube, I have a video posted of the car right after I finished installing the dual exhaust and glasspacks. The sound quality isn't great as it was shot on my wife's cellphone, but it will give you a good idea of how loud it is.

Mounting them further up towards the engine will usually make them quieter as well. If you're planning on running the pipes down the trans tunnel, you could look into GMMG boom tubes. They can be mounted in the trans tunnel and aren't much thicker than the exhaust pipe. Then you would only need to route the tailpipes out the back. No need to try and mount mufflers under the rear of the car. There used to be a few members on here that had them, so you should be able to find some good pics with a search.

 

Thanks for that. Now a sound clip is needed!
Was it much of a chore for the duals down the trans tunnel? I've seen a few pictures of installations but nothing that would show the ground clearence.

 

Here is the link to my Youtube clip:


I ran the exhaust in the stock location, not down the trans tunnel. I used the Dynomax kit for Thirdgens on Summit Racing. It fit pretty well, but I did have to modify a few sections for a better fit. I posted a build thread on here in the Exhaust section detailing the entire process.