Which unmodified mufflers act as pressure wave termination box?

[Fireonthemountain]

Ah, many tricks and treacheries, in racing anywhere I am glad to say

Of course human errors and assumptions bloom naturally even without intent. I really don't like having a very loud car at all right now in my life, for several reasons. It irritates cops from miles away and can make the mechanical sounds of a car hard, or impossible to hear.

We maybe need a separate thread on street racing tricks, and exhausts. I am game

[user-23911]

I find that those rotary mufflers work really well, the ones that look like hair dryers.

[pdq67]

I find that those rotary mufflers work really well, the ones that look like hair dryers.

joe,

What brand are the rotary mufflers you are talking about?

I haven't heard of them is all.

pdq67

[Aukai]

PSSST Paul.... (turbos)

[ptuomov]

I would like to ask,and I have read this late at night, and hope I make sense. I have a 70 Chevelle with a 900+ hp 7500+RPM 572 with 2 1/4" headers, 3.5" exhaust with X pipes, and 20" Magnaflow mufflers before the rear end. How would adding 3" tail pipes over the rear end, and out of the back effect performance?

I wouldn't step them down after the mufflers, but my extensive exhaust testing doesn't involve mufflers. Going smaller with the cross section the farther down stream theory goes against anything I've ever found.

If the noise is not a concern, then I would guess that slowing the exhaust gas down by expanding the area works well.

With a noise constraint, I am thinking that one wants to minimize back pressure within that noise level constraint. My logic says that letting the exhaust gas cool allows one to use a smaller pipe in the back of the car without increasing the exhaust gas velocity. Then, by placing the mufflers as far back as possible, one can increase the ratio of muffler case cross-sectional area to the exhaust pipe cross-sectional area, which makes the exhaust quieter.

[Fireonthemountain]

Basically along the line of what these guys found with their testing

http://www.pontiacstreetperformance.com ... haust.html

The further back the better for the mufflers, and what comes after the muffler, as far as tail pipe size is not really important. Then I though back to factory designs and how the mufflers on a high performance car was usually all the way at the back, like my L78 Camaro was with resonators. In my mind the Aero Hooker just before the axles will act like the resonators, though even better flow, and then what comes after them will not matter maybe so much, such as curves or mufflers or pipe size.

This idea of the Aero Hookers first has other reason for this idea, for me as well from a longer lasting street point of view, as I think the turbo mufflers will be more stable and not change tone, so much over time. The Aero will take the first hot dirty blast filtering it some perhaps some of the carbon and heat as well as averaging the blast pressures spreading them out over micro seconds being sent through the curves in the pipe to the Turbos. It should also work on different sound frequencies for each style of muffler. But at no point is this meant to be restrictive really, to quieten it more, though thats a nice side benefit in certain ways.

OK, I am going to do some time travel and drop back a thousand years. The first all business Hemi street racer car from Detroit's hey day street racing, in the 60s I got to see pictures of later had a very odd exhaust set up I thought then. Two small side by side mufflers Corvair turbo type mufflers off each of the header collectors, with no pipe after them. I thought then it was light weight, cheap, but effective probably for meeting the muffler laws then.

But my brain didn't really click on this until well past 2005, when I got to see another street racer's car's pictures belonging to a pretty hard core E/stock class racer called Bill Travato. There at the back of his street 442 sat large side by side mufflers, for each side. Then the concept fully clicked in my brain. Divide the sound and hot air flow into 2 mufflers. This should provide virtually no flow restriction with virtually any type of muffler. The downside for some would be half the flow, so half the air speed and heat would mean twice the time the exhaust would spend, in each muffler resulting a very very quiet ride. But flow, and tuning for maximum ET is a little different, or can be.

Now back to our regular scheduled programming...........I will shut up now.

[pdq67]

PSSST Paul.... (turbos)

Thanks Aukai, but I thought that we were talking about mufflers here is all.

I have said this many times, but imho, the old W/D/T smooth perforated inner pipe REAL glass packs are probably the best.

If they cackle too much to suit you, then add them end to end together down each side. My hopped up 409 that I put in my 1st Gen. Camaro had three down each side.. Totally straight thru so minimal restriction...

Or, like said, "Y", them down each side.

pdq67

[ptuomov]

I have said this many times, but imho, the old W/D/T smooth perforated inner pipe REAL glass packs are probably the best.

I completely agree with you on that you've said that many times.

[pdq67]

He, He!!

pdq67

[RevTheory]

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: ?

[Carnut1]

IMG_20130608_182057_089_resized.jpg

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

[RevTheory]

I've run dual Aerochambers at 485 hp before and they had one hell of a snap without terminator boxes and a crossover. Down right loud! This is before the boxes blew apart for the 3rd time and I finally just pulled them out.

Box2.jpg

[Bazman]

Reading this thread reminded me why I want to make a few mufflers before I die to share what has worked for me.

Like a rifle silencer, sound waves lose significant energy instantly with a sudden increase in volume. The energy is further lost if they have to bounce off walls repeatedly back and forth, cancelling each other out. The 1st does not hurt power necessarily, the 2nd is a challenge to not add backpressure... but do-able.

There will be exceptions, so forgive me here for being general... most race car classes have a minimum weight. IMO mufflers are not the place to be looking to save weight. I laugh when I see people spend mega bucks on a titanium exhaust only to sound like a cat thrown into a tin barrel of Hades with a witch - when some carbon fiber in other strategic areas would have saved more weight and achieved more.

Light mufflers cannot function as well as a heavy muffler of the same design. Many here can attest to the fact that a well designed good ol cheap exhaust tubing exhaust is quieter than the same thing in stainless, and the thicker steel tube exhaust/muffler sounds better, deeper, is not raspy. Raspy is not "exotic", it's just raspy, it's like Rod Stewart singing alongside Pavorotti, but he's a rock star so we kid ourselves he's better.

The good news is that a really good race car needs ballast to bring it up to minimum weight. Mufflers are THE PERFECT way to get that done, nice and low. I'd even cut into the floor pan and make room for a couple of decent "boxes" (hint), which leads me to my main point...

there is one fundamental common design feature found in almost every muffler made.... their shape.

But why are they all like that? Sound is happy to wrap itself around a curve and shoot straight out into your eardrums. Think about it.

Sound does not however like to bounce off walls. If it does that enough it definitely starts to lose its mojo. That is why lots of chambers work but for us guys at the high cost of backpressure...

So... what if the muffler itself was not oval?

Add to that: volume, then insulate and double skin it, where one skin is double the thickness of the other with a small air gap between. Straight through, no power loss. Need ballast? Throw some lead sheet in and insulate it from the heat (won't be an issue on a street car unless exhaust exit too close to heat source). Result? Quiet as some muscle OEM's at idle and normal driving (like passing cops); at WOT sure it'll be louder than OEM but it will pass the strictest race track sound regulations. The sound reduction will then become a function of volume and weight. Resonance is a simple J pipe away from being eliminated once you calculate the length required. On a turbo car these can be unsurprisingly small.. and I did use stainless because I wanted to be sexy, but it was thick gauge. No need for electric by-pass cut-offs etc done this way as long as you have (or make) room

[ptuomov]

Reading this thread reminded me why I want to make a few mufflers before I die to share what has worked for me.

Like a rifle silencer, sound waves lose significant energy instantly with a sudden increase in volume. The energy is further lost if they have to bounce off walls repeatedly back and forth, cancelling each other out. The 1st does not hurt power necessarily, the 2nd is a challenge to not add backpressure... but do-able.

There will be exceptions, so forgive me here for being general... most race car classes have a minimum weight. IMO mufflers are not the place to be looking to save weight. I laugh when I see people spend mega bucks on a titanium exhaust only to sound like a cat thrown into a tin barrel of Hades with a witch - when some carbon fiber in other strategic areas would have saved more weight and achieved more.

Light mufflers cannot function as well as a heavy muffler of the same design. Many here can attest to the fact that a well designed good ol cheap exhaust tubing exhaust is quieter than the same thing in stainless, and the thicker steel tube exhaust/muffler sounds better, deeper, is not raspy. Raspy is not "exotic", it's just raspy, it's like Rod Stewart singing alongside Pavorotti, but he's a rock star so we kid ourselves he's better.

The good news is that a really good race car needs ballast to bring it up to minimum weight. Mufflers are THE PERFECT way to get that done, nice and low. I'd even cut into the floor pan and make room for a couple of decent "boxes" (hint), which leads me to my main point...

there is one fundamental common design feature found in almost every muffler made.... their shape.

But why are they all like that? Sound is happy to wrap itself around a curve and shoot straight out into your eardrums. Think about it.

Sound does not however like to bounce off walls. If it does that enough it definitely starts to lose its mojo. That is why lots of chambers work but for us guys at the high cost of backpressure...

So... what if the muffler itself was not oval?

Add to that: volume, then insulate and double skin it, where one skin is double the thickness of the other with a small air gap between. Straight through, no power loss. Need ballast? Throw some lead sheet in and insulate it from the heat (won't be an issue on a street car unless exhaust exit too close to heat source). Result? Quiet as some muscle OEM's at idle and normal driving (like passing cops); at WOT sure it'll be louder than OEM but it will pass the strictest race track sound regulations. The sound reduction will then become a function of volume and weight. Resonance is a simple J pipe away from being eliminated once you calculate the length required. On a turbo car these can be unsurprisingly small.. and I did use stainless because I wanted to be sexy, but it was thick gauge. No need for electric by-pass cut-offs etc done this way as long as you have (or make) room

Very interesting post, and I've though about similar issues.

About gun silencer analogy: https://www.speed-talk.com/forum/viewtopic.ph ... 95#p672812

About chamber shapes if the exhaust has supersonic shock waves: https://www.speed-talk.com/forum/viewtopic.ph ... 80#p672784

About radiation thru the case and double skinning the case: https://www.speed-talk.com/forum/viewtopic.ph ... 65#p670675

[Bazman]

Very interesting post, and I've though about similar issues.

About gun silencer analogy: https://www.speed-talk.com/forum/viewtopic.ph ... 95#p672812

About chamber shapes if the exhaust has supersonic shock waves: https://www.speed-talk.com/forum/viewtopic.ph ... 80#p672784

About radiation thru the case and double skinning the case: https://www.speed-talk.com/forum/viewtopic.ph ... 65#p670675

Very cool

I've also looked hard at gun silencers - they'd work great but hurt power significantly because the gas wants to escape with the sound waves which would create backpressure.

Re chamber shapes - Agree with you on "d" for same reason as above i.e. lowest backpressure, sound escapes but gas is encouraged to keep going. What is missing is that the "glass packing" (there are better materials now than glasspack) needs to be thin enough for sound to pass right through and the muffler large enough to have an open chamber around it for sound to bounce around in off the straight walls. Ideally hitting walls lined with denser sound insulation (lead sheet is amazing long as you don't tell the greenies and keep it under melt temps, I'd wrap it in kevlar cloth or similar, but have been looking for a lighter alternative that is as good at sound absorption).

Radiation - interesting chart I have tried cutting a slot in the pipe exit in the space between the inner and outer skins on the theory the sound would be trapped and cancel itself out. Didn't work, so I either didn't do it right, or the double skin is best left isolated .