Which unmodified mufflers act as pressure wave termination box?

[travis]

Let's say you needed a full exhaust on a short bed truck that would support roughly 450-475 hp and the collectors exit at 2.5 inches and you wanted to end up single out-

Option 1: Would you dump each collector into a highflow cat (Pipemax length), out of the cats at 3 inch, cross one side over into an x pipe, keep the duals on the same side of the truck and into a pair of 3 inch Borla-style (Magnaflow, Dynomax, straight-throughs), into a 3 in/ 3.5 (4?) out y pipe on out the back?

Option 2: Cross one side over somewhere safe under the bellhousing, trans, transfer case, into a 2.5 in 3 out y pipe (again, Pipemax length), single highflow cat and long as hell straight through muffler of the sort mentioned above?

Option 3: ?

Do you have to run cats?

I’m looking at a similar (minus the cats though) system for my short bed truck. 2 1/2” collector outlets, drivers side routing over to the passenger side, dual 2.5” in/single 3.5” out y-pipe, into a 3.5” in/out straight through motor home type (long) muffler, and a single 3.5” tailpipe exiting behind the rear tire. There are several choices in this type muffler...I’m just waiting on confirmation e-mails that they don’t neck down internally. I have dual tanks so I don’t have much choice

[ptuomov]

Let's say you needed a full exhaust on a short bed truck that would support roughly 450-475 hp and the collectors exit at 2.5 inches and you wanted to end up single out-

Option 1: Would you dump each collector into a highflow cat (Pipemax length), out of the cats at 3 inch, cross one side over into an x pipe, keep the duals on the same side of the truck and into a pair of 3 inch Borla-style (Magnaflow, Dynomax, straight-throughs), into a 3 in/ 3.5 (4?) out y pipe on out the back?

Option 2: Cross one side over somewhere safe under the bellhousing, trans, transfer case, into a 2.5 in 3 out y pipe (again, Pipemax length), single highflow cat and long as hell straight through muffler of the sort mentioned above?

Option 3: ?

Not pretending to be an expert, but what flow capacity cats do you have available? Do you have to just have cats or do you also have to pass some sort of emissions test?

[RevTheory]

I was looking into Random Tech for cats but it looks like supplies are limited as they seem to have gone under. MagnaFlow has a 3 inch in/out and if it flows anything like the Randoms, it should be up over 500 cfm. Probably need two, huh?

I don't know if cats will be mandatory but probably so. Plus, I think I can use it as terminator box without building one that will just blow apart anyways. I can extend the 2.5 inch collector extensions into the 3 inch inlet an inch for an anti-reversion step and probably have the cat pull a little snap out of the exhaust note, although the whole thing may just be wishful thinking on my part.

I sure think I want to go with one of those 5 or 6 inch diameter, 20+ inch length, straight-through mufflers, though. I forget if it's MagnaFlow or maybe DynoMax has them rated at 2,200 cfm. I just don't know how loud the damn things are. I'm not 18 anymore

[ptuomov]

I was looking into Random Tech for cats but it looks like supplies are limited as they seem to have gone under. MagnaFlow has a 3 inch in/out and if it flows anything like the Randoms, it should be up over 500 cfm. Probably need two, huh?

I don't know if cats will be mandatory but probably so. Plus, I think I can use it as terminator box without building one that will just blow apart anyways. I can extend the 2.5 inch collector extensions into the 3 inch inlet an inch for an anti-reversion step and probably have the cat pull a little snap out of the exhaust note, although the whole thing may just be wishful thinking on my part.

I sure think I want to go with one of those 5 or 6 inch diameter, 20+ inch length, straight-through mufflers, though. I forget if it's MagnaFlow or maybe DynoMax has them rated at 2,200 cfm. I just don't know how loud the damn things are. I'm not 18 anymore

I am not an expert, but I'd probably do the following.

Calculated collector length and then an H-pipe after that, located per PipeMax. The H-pipe is your anti-reversion system and termination box all in together!

Step up to 3" after the H-pipe with a smooth transition and run it to a cat on both side. Magnaflow 3.5" cats seem to use the same flow capacity cell so 3" flows as well as 3.5" cat, so 3" I/O cats are what I'd go with. 3" I/O here is not the restriction, it's the cell, IMO, so I/O only matters to the extent that large I/O cats also have better flowing cells and transitions to/from the cells.

After the cats, the question is whether the layout is better for a single exhaust or dual exhausts. Which way can you fit more muffler volume under the car?

[RevTheory]

That's definitely doable if cats aren't a requirement. I've never heard a crossover prevents reversion but it sure knocks the sound back and I could use the 2.5 to 3 inch expansion as a bona-fide anti-reversion step. Doing it your way would also free up roughly 10 inches for smoother bends and/or a longer muffler.

Thanks (we need a thumbs-up emoji)

[ptuomov]

That's definitely doable if cats aren't a requirement. I've never heard a crossover prevents reversion but it sure knocks the sound back and I could use the 2.5 to 3 inch expansion as a bona-fide anti-reversion step. Doing it your way would also free up roughly 10 inches for smoother bends and/or a longer muffler. Thanks (we need a thumbs-up emoji)

We ended up getting cats with V-band clamp flanges welded to them and then also stainless resonators of the same I/O dimensions. We can swap those depending on the mood and other things, while keeping sound reasonably consistent:

Resonator that works as the test pipe when the cats aren't installed:

[travis]

I’d bet dual 3” dynomax super turbos would work very well here with minimal (if any) loss of performance on the very top end. The noise level difference between dual 2.5” 18” long straight through mufflers and dual 2.5” 18” case super turbos is literally night and day, whether behind a 210hp 351w or a 375hp 351w.

With the straight through’s on the truck with 3.55’s and no overdrive, the noise was obnoxious within minutes at highway speeds. With the super turbos, you can drive for hours on end quite comfortably, and they still sound good I think.

[pdq67]

A big cat, imho, is the stock one on a 1980 C/10 P/U with the 1-piece head 250", 6-banger in it.

Not knowing any better, I put one back on mine when I started to rebuild it and then found out that it wasn't REQUIRED until 1981 to pass inspection.

It's a tubular ceramic monolithic cat with a 3" in, but sorry, I forget out?? I think it also is 3"s??

FWIW, the I-piece head 250" 6-banger engine has split cast-iron exhaust manifolds on it stock. The spilt "Y"'s into the cat so it is big..

pdq67

[RevTheory]

I’d bet dual 3” dynomax super turbos would work very well here with minimal (if any) loss of performance on the very top end. The noise level difference between dual 2.5” 18” long straight through mufflers and dual 2.5” 18” case super turbos is literally night and day, whether behind a 210hp 351w or a 375hp 351w.

With the straight through’s on the truck with 3.55’s and no overdrive, the noise was obnoxious within minutes at highway speeds. With the super turbos, you can drive for hours on end quite comfortably, and they still sound good I think.

Maybe like this- http://www.dynomax.com/super-turbo-offs ... 18006.html

I don't think a single at 700 cfm is going to work though.

Edit: This is the other one I was looking at but I can't find any flow numbers or sounds. I guess I could try the rabbit hole known as youtube but I'll likely spend an hour and a half and then forget what the hell I was there for to begin with

https://www.magnaflow.com/products?partNumber=12641

[ptuomov]

Can one fit more muffler case volume (after cross-over and cats) with a single or dual exhaust?

[midnightbluS10]

I’d bet dual 3” dynomax super turbos would work very well here with minimal (if any) loss of performance on the very top end. The noise level difference between dual 2.5” 18” long straight through mufflers and dual 2.5” 18” case super turbos is literally night and day, whether behind a 210hp 351w or a 375hp 351w.

With the straight through’s on the truck with 3.55’s and no overdrive, the noise was obnoxious within minutes at highway speeds. With the super turbos, you can drive for hours on end quite comfortably, and they still sound good I think.

Got a single Dynomax super turbo muffler on my DD with 2.5" catback. It sounded very close to stock. I couldn't tell much of a difference in back 2 back testing. Removed the cat and the sound increased dramatically. It sounds much, much better. I was actually quite surprised at how similar it sounded to stock. Wasn't expecting that.

[travis]

I’d bet dual 3” dynomax super turbos would work very well here with minimal (if any) loss of performance on the very top end. The noise level difference between dual 2.5” 18” long straight through mufflers and dual 2.5” 18” case super turbos is literally night and day, whether behind a 210hp 351w or a 375hp 351w.

With the straight through’s on the truck with 3.55’s and no overdrive, the noise was obnoxious within minutes at highway speeds. With the super turbos, you can drive for hours on end quite comfortably, and they still sound good I think.

Maybe like this- http://www.dynomax.com/super-turbo-offs ... 18006.html

I don't think a single at 700 cfm is going to work though.

Edit: This is the other one I was looking at but I can't find any flow numbers or sounds. I guess I could try the rabbit hole known as youtube but I'll likely spend an hour and a half and then forget what the hell I was there for to begin with

https://www.magnaflow.com/products?partNumber=12641

It looks like you have plenty of room for duals, so I think 1400 cfm will work very well, and be a lot quieter than anything straight through.

[travis]

I’d bet dual 3” dynomax super turbos would work very well here with minimal (if any) loss of performance on the very top end. The noise level difference between dual 2.5” 18” long straight through mufflers and dual 2.5” 18” case super turbos is literally night and day, whether behind a 210hp 351w or a 375hp 351w.

With the straight through’s on the truck with 3.55’s and no overdrive, the noise was obnoxious within minutes at highway speeds. With the super turbos, you can drive for hours on end quite comfortably, and they still sound good I think.

Got a single Dynomax super turbo muffler on my DD with 2.5" catback. It sounded very close to stock. I couldn't tell much of a difference in back 2 back testing. Removed the cat and the sound increased dramatically. It sounds much, much better. I was actually quite surprised at how similar it sounded to stock. Wasn't expecting that.

Most cats definitely “muffle” as good or better than most mufflers.
On my suburban however, it has a factory installed big block stainless steel exhaust that is dual 2.75” pipes into dual, small case 3” in/out cats...which muffle nothing on a 255hp L31 smallblock! From the cats it is dual 2.75” pipes to a giant dual in/single 2.75” muffler that had been deleted before I bought it, replaced by a y-pipe to connect the duals to the single tailpipe. It sounded terrible IMO. I ended up having Spintech make me a dual 3” in/single 3” out “RV 8000” series muffler. It sounds really good...and no drone.

[ptuomov]

Here's one opinion that may or may not be controversial. Let's take a look at this David Vizard graphic:








When the glass-pack mufflers were long tubes that were maybe an inch larger diameter than the pipe (not a very good muffler), this may have been accurate.

However, if you look at the current large-case Borla or Magnaflow packed mufflers, they behave more like the "Flowmaster" box muffler in the graph and less like the skinny glass pack. This is because, for those more modern mufflers, the case dimensions and the porosity of the inner perforated tube are way more important for pulse tuning than whether the muffler case is packed or not. If you have a large-case Borla or Magnaflow muffler with a high porosity in the perforated inner tube, that's going terminate the pulses approximately the same as an empty big can, but without annoyingly passing thru noise at some frequencies. This is because there's so much free air inside the packing material and the packing material further absorbs the pulses. The less hole area there is in the perforated inner tube and the smaller the case volume, more it will look like the David Vizard's glasspack.

Therefore, if you can put two large-case Borlas in the exhaust right after the x-pipe or h-pipe, that's in my opinion going to be for all intents and purposes a termination box. Just an opinion, of course.

[Fireonthemountain]

IMG_20130608_182057_089_resized.jpg3" in ganged 3" Hooker Aerochamber 3.5" output. Not exactly quiet but not bad. Old work truck 355.

Slight overkill me thinks on size, and even more so with ganged mufflers, though I do like the basic design. 2 1/2 would have served it better me thinks, and should have had no real restriction below 500hp or there abouts.. It should have been quieter at 2 1/2. Past the first mufflers the sizes may not matter much, as you should need less flow area with the now cooler condensed gases. You could use even smaller pipes, and or a seconds set of mufflers of a different type.

I can say this. With a 461 coming off OEM manifolds into 2 1/2 of pipe, then in a few feet a set of 3 decade old worn out sonic turbos, and then into 2 1/2 pipe exiting in front of my back tires. It has a lot of pop/thump at idle coming out the pipe.

I then added statically an aero chamber on to the exhaust pipe's end with my hands and listened. I still could hear some sound out of the aero chamber, though not much at idle. I then tried exactly the same thing with a large case (20" case) dynomax turbo muffler, and all sound was gone at idle besides the airflow coming out, without extra pipe on either muffler on their exit tubes.

It was just a cheap meaningless experiment to most, but to me it confirmed my idea for a high flowing, but fairly quiet exhaust without thump with also increase flow was possible. I would double gang them if I wanted more than say about 400hp possible with 2 1/2 single mufflers. Or just run straight pipes if the laws allowed, and no inspections here where I live.

Double ganging mufflers = straight pipes on flow and now you have twice the silencing as well. Running them is series is common today. My view is first pair double ganged pair, then into another single serial muffler probably would not restrict flow and without going to larger sizes, but kill the sound.

Silencers on guns restrict flow and slow bullets down. So there is no magic there, that I am aware of, since there is a trade off. But with bullets that doesn't matter 99.99% of the time because they are still plenty lethal from 22 shorts on up. Subsonic or not.

The message there for cars might be slow the speed down of the gases exiting, without restricting flow. Subsonic is a lot quieter, with bullets or planes. No crack from breaking the sound barrier.

Here is another point, as you increase pipe sizes you lose the cooling efficiency of the gases it has. Less surface area for cooling versus more volume percentage wise.