This is a legitimate question, I would like to hear from anyone that is an exhaust expert to understand why this idea would not work and what if anything could be changed to make it effective. I'm not an expert myself and just want some feedback on this idea so please be nice in your reply.

Below is a crudely drawn image of an exhaust system idea that is not particularly to scale. This idea was born from reading another exhaust thread where it was said that the reason why a corvette's exhaust is not throatier is due to the mufflers being so far back in the system. The idea behind this system is to allow the mufflers to be further forward in the car. Legend: red=muffler, blue=round tubing, purple=oval tubing and green=oval to round transition. Since the pathway is a bit narrow, the drawing is supposed to show two relatively narrow round mufflers, staggered with oval tubing to allow for a larger diameter tube while passing the muffler. Is it important that the length of the muffler system is equal both before the muffler and/or after, or is total equal length the important part? If equal before and after is important, could this be made up by having an s-bend to extend and equalize the tube length on either side?

I would love to hear from @GREGGPENN who had some seemingly expert opinions on the prior thread linked, if he's still active on the forum.

 

First of all, I'm not an exhaust "expert". I've used a combination of sound (speaker building), vizzard theory, several iterations of my own exhaust systems and reading feedback from this forum (over the years) to form opinions. Several would qualify for similar reasons.

I don't like the design shown because it less "straight-thru" than alternatives. While it's not beyond things I'd dream up, it clear almost every member is interested in maximum performance. Adding bends defeats that. I'd also wonder how it would affect resonance -- if different "setups" created slightly different "notes" and a dissonance? Probably not...but it's another reason I wouldn't spend money on that experiment.

Muffler/CAT selection, pipe size, and pipe length are more prominent in the final "sound". Also, being "throaty" is a subjective description that might mean different things to different people. I'd consider it a somewhat higher "blaaat" kind of sound. Someone else might consider it deeper. Corsa mufflers are most often described as throaty and though expensive would be my first thought for your quest. For a less expensive solution, I like the idea of glass packs (probably WITH bullet converters) and that's it. There's enough room "in the belly" to put two 4" long, round mufflers side-by-side....which is what I'd suggest as an alternative to Corsas. "Theory" would dictate going as small or smaller downstream from the mufflers. If you want to increase or open-up sound ... as a more primary goal, I'm wondering if you'd like 3" pipe -- at least after the mufflers. I'd think that would increase the "BLAAAT" effect.

For comparison, the 383 (sidepiped) setup I've run since 2010 is effectively bullet cats and glass packs .... running through 2.5"...then 2.75" piping.

Without sidepipes, you'd have less bends and shorter exhaust...which would make it somewhat louder.

I can't think of what you call oval outlet pipes on a motor bike, but they create a "blaaat" sound too. Point being... oval-shaped outlets might also be worth trying -- for your goal.

 

A lot of sound is subjective as @GREGGPENN said. I personally think that on the earlier cars a lot of the sound loss comes from the merge at the center and sudden expansion at the cat.

While I agree that bends and such do not help performance, iirc @Tom400CFI built a nice sounding system on his vette kart and I believe his solution for better sounds was to make it bendy. (Or maybe that was another car, I can't recall at the moment)

Exhaust sound is very subjective. I consider mine throaty but thats me. I would also consider Gregs throaty as well. ​​

 

..... Why don't you take up your own theoretical challenge and BUILD IT ! ... give those of us who struggle with theory something to hear ... perhaps you have stumbled on a new career opportunity ? Fame and fortune awaits ?!?..... It has also been scientifically suggested that mufflers at the end of the plumbing (as on our beloved Corvettes) can contribute to the resonance issues that we encounter .....

 

Not suggested, proven. Every car I have dealt with that has mufflers in the rear requires expensive, well engineered muffler set ups to combat the resonance. The cheaper universal styles, even when sold as a custom fit (Looking at you Flowmaster), drone horribly. Certain high end systems even employ helmholtz chambers. Google it and you will see them. Some people have added, others come as part of the system.

 

^He's right. The Kart is where I found some success. The whole thing started when I had my C6, which I feel, sounded like poo. I bought 2 and built 3 different exhausts on that turd and all were a total failure. I never once heard a nice sound out of the back of that car. I feel that the the C4 has a similar characteristic, though not as bad, and with the Kart, I figured that I'd try something different. It appears to have worked, BUT....when I threw in an "H", it kind of went to **** again....so I'm still thinking about it. Why does one car sound so luscious and another sounds so lame....with the same exact engine Why do F-bodies sound so awesome, and 'Vettes....don't? It's a lot of reading, but here is all my experience compiled into one thread, right HERE
The "gold standard" for sound, in my mind, is most any Fox body or SN95 Mustang. I just love that bubbly, rich, luscious, "3D" sound! The most revealing comparison in my mind, is the 05 GTO vs. any early C6; they both have the exact same, LS2, 6.0L, 400hp engine. SAME. But the GTO sounds awesome with most exhausts and the 'Vette sounds like poo. Where is the difference?

 

..... I cannot attest to the sounds made by my heap as I've never heard it in drive-by mode but I have had ... on 2 separate occasions ... had someone find me in the pits at the track and ask for the formula because they liked what they heard . Mine has long tubes feeding into 3" tubes , a nice X-pipe , then 2 generic bullets ... more 3" tubes into Flowmaster 50 series mufflers . Y'all are welcome to come and lend an ear at Bradenton for the Turkey Bash or the Snow Bird Nats the following weekend . Somewhere on this Forum are a couple of videos of my junk on an 1/8th mile pass running a Tesla ... so mine is all you hear .

..... Found it ... but theres someone doing a burnout just after I launch that muddies up the down track noise ... https://drive.google.com/open?id=1X7...rHa2gITItqnPVf

 

Thanks for the replies everyone. I'll keep thinking on it and learning more.

 

Do you have a video to demonstrate final sound...if not before/after on what you did/liked? I didn't want to read through 14 pages just to satisfy my curiousity. I jumped to the last page...in case it's where final conclusions and/or a vid might be. I found it curious the last page starts with a quote about lengthening exhaust to make it sound better. The sidepipes on mine create an unusually long setup. Longer than anyone would EVER do consciously. I admit being curious who finds the sound "good" and/or how it compares to what YOU liked in your experiments? Occasionally, I wish it were louder.

In speaker building, ported bass systems (cabinets) can be "tuned" higher/lower -- changing the resonance of the cabinet. WHERE the resonance is controls where bass notes are "amplified". Longer tubes means lower tuning. As mentioned, my sidepipe setup is extra long...implying a lower tuning. The promo (sound) recording for Side-Effects included and "advertisement benefit" of no resonance because the exhaust note is lower with Side Effects. To be honest, I've never tried recording exhausts in an attempt to discern frequency. It might be worth considering. I don't remember anyone thinking of that. (FWIW, I saw a YT vid on measureing the frequency of electric motors by recording them ... and measuring the frequency using a cell phone. Probably was I didn't recognize the "analyzer" shown on the phone in the vid. And, it wasn't referenced. Maybe it's on an iPhone...which I don't have? Or maybe it's an app?)

The point of this post is to suggest exploring the frequency of exhausts...possibly as a function of length.

 

Maybe this is my problem... only subwoofer I've built was sealed. Guess that don't work well on exhaust.

In all seriousness though, its similar enough that it applies but you're dealing with steady state flow vs pulses... (close enough anyway) so models would more trend toward the idealized model.

By adding bends you are I imagine creating some reflections... thus changing the sound... post 255 in the thread tom linked and then click the link and post 142 has a video.

 

You should probably read the whole thread. It was suggested many times in the thread, that longer exhausts sound better. That was also debunked....many times. But....then you get guys like "mikeCsix", who don't read the thread, and go ahead and post in post 260....that longer exhaust sound better.
That's why buses and UPS trucks sound SO sexy!

Anyway, In that thread, I posted a vid of a black '05 GTO (post 137) idling, revving, then doing a burn out. Dear lord, that thing sounds delicious. LS2 engine. I didn't realize it until now, but I never actually went back and posted my Kart vid in there. I'll go update it...

 

"Pissed" Exhaust thread updated w/vids.

 

Staggering them could cut down on the resonance

Look at how this airbox is shaped. Puts the Heimholtz theory to work .
Thats why those "cold air" kits which just has a tube make so much noise...guys think it equates to more power...actually it turns their factory cold air into a hot air system. Anyways...

 

For clarification, 4" long, round mufflers (in my post above) means 4" diameter, long glass packs. I think they make them up to 24" long... I've posted before that smaller-bodied mufflers have sounded better to me on C4s. In effect, I'm talking about: bullet cats, glass packs, and targa mufflers. My side pipes also use glass packs. I've heard/had 3 mufflers with a larger body: the quiet factor mufflers, a turbo-style, and a spin-tech. The last time I changed my set-up, I removed the Spin-Tech, the improvement was stark... It got slightly louder (in a good way), and the sound quality really improved. My conclusion is that (unless VERY WELL engineered, mufflers are an echo chamber that can/does induce "ugly" sound. Factory mufflers contain so many chambers/batting that you don't hear it. I think of this along the line of speaker tuning (mentioned above).

Heimholz chambers (that cancel sound) also prove (to me) that mufflers can induce "bad sound". In the thread Tom posted, I'd question if the GTO and Corvette had the SAME exact muffler/cat systems? His question was how a GTO, Corvette, Mustang can sound different behind the same engine?

I actually don't know what engines are in Ford's these days...especially in terms of firing order. For our generation, it's been noted that firing order of Ford is different (better?) than Chevy. I'm talking about sound anyway. You can even buy a cam to convert Chevy to Ford's firing order! That doesn't address the GTO vs Corvette (LSx) difference, but it may revive a difference not recently talked about. And, yes, I've long admired the Ford exhaust note. Never owned one though. Probably won't....especially after watching history of Ford vs Ferrari...and Ford's history on the History Channel! LOL

 

Interesting about your experience w/the Spintech...and "ugly sound".
The GTO and the 'Vette definitely have different mufflers. Everything from the manifolds back is different. Same goes for the '06-'07 CTS-V; same LS2 engine...totally different sound and a different exhaust. Oddly, the stock CTS-V is louder than a stock C6. Anyway....way different sound from cars with the same exact engine.



The LS has the same firing order as the Ford, if you re-number the Ford cyliders the same as the Chevy ones (or vice versa)

 

And its only the same as the HO Ford firing order. The regular 302 ford and say 350 chevy firing order are identical. The only real reason for the switch was it provided the smoothest read off the reluctor in an LS.

 

That's why I posted that piping/mufflers appear to have way more to do with the sound...than the engine. Except, why hasn't anyone gotten a 6 to sound like a V8! :-)

One reason the GTO video sounds so good is the "echo chamber" formed by all the concrete in that parking area. I really like the sound of mine bouncing off walls/concrete.

Whether it's my personal preference, I like mufflers that suppress any "metallic" sounds....making the exhaust note more pure. The Corvette vid (because of the big cam) had that "extra" metallic distraction. The GTO didn't. I need to listen to the Kart video on my big speakers.

 

Copy that. I don't like the "metallic" (aka, "European" sound), either. But mostly, I don't like the "2 dimensional" sound of newer 'Vettes. How the tone rises and falls w/RPM, but there is no tonality to the V8 burble at all.

Blaaah-blaaah-blaaah-blaaah-blaaah-blaaah...at idle. It just totally lacks that lusty, rich sound that better sounding cars have. Cars other than the Y body.

The Kart vid has some distortion when I get on it, but I think you can at least get an idea of how it sounds.

 

I didn't think about this enough. It would explain Tom's statement (observation). Plus, if you consider my thought about speaker building...and bass ports, having the mufflers so near the outlet is likely to perform like a ported speaker with a short port. As pointed out, the exhaust "note" is comprised of pulses. When they hit turns -- or the muffler -- I imagine the restriction causing the pulses to pile up. I feel like their dynamic changes...where the outlet of any restriction somewhat becomes a new starting point....because the force/velocity seems likely to change.

As I listened to a few more exhaust vids (including Toms), I noticed the best exhausts have a clear low-end rumble but also transition nicely with rpm. Others are less "musical" and stay muddy...and/or don't "evolve" enough with rpm variations. This "stagnation" seems likely to cause resonance as well. Picture a changing tone from a synthesizer lagging while pitch rises. IOW...if you don't hear a clear, unique, defined tone.

A standard muffler is a box where sound waves can bounce off surfaces and interact with each other....and not in a way that improves, amplifies, or cancels. I think a box muffler muddies exhaust sound. For one thing, their design contracts speaker-building theory -- where no dimension should exceed twice that of another. Placed forward enough in the exhaust, mufflers have a chance to be cleaned up. Piping refocuses sound in a linear fashion...just like a wind instrument.

Perforated x-pipes, glass packs, chambered pipes, cats, and other sound abatement mufflers that are "straight-through" would be less guilty of muddying the note. Maybe that's why I like them...no matter where they are placed (including the targa mufflers -- that were my first mod (over stock) in 2001. A standard muffler "box" that's close to the exhaust exit might let you hear the muddiness going on inside. It's exit (a Corvette exit) might be too short to allow the exhaust note to refocus.

When I said "ugly" before, muddy would have been a better adjective. When I removed my SpinTech, the exhaust was a bit louder -- but more defined. There's nothing in my system to muddy it.

Conversely, bends, chambered pipes, and perforated straight-thru pipes might soften some of the bass -- so it doesn't get overwhelming...and muddy. You might think this a contradiction from my thoughts about a box causing muddiness -- but the exhaust/sound doesn't have enough chance to bounce around (inside a secondary acoustic environment). Think of that cone they put in front of trumpets...to mute it. It mutes all sound...but high frequencies more. Maybe bends and chambering (without being boxy) act like an attenuator...that make bass a bit more apparent and removing a bit of high-pitched rasp? Plus, the note changes freely -- without having to fight a box having it's own acoustic/resonance properties.

P.S. If you think there's a lot of scientific proof in this post, refer to the post title! LOL

So...How about a random untested conclusion. I think the OP's design wouldn't sound bad. It probably would sound better than a lot of other options. My thought is it would sound even better IF the mufflers were 4" round glass-packs or chambered pipe vs. something like a Magnaflow or Flowmaster muffler. You know...an oval.

 

While I'm not an "expert", I was lead tech advisor at Flowmaster Muffler for 2 1/2 years (although it's been quite a while) so I'll put my 2 cents worth in here.

As for Flowmasters droning - that's typical when the wrong ones are used. Typically shops will sell 2 chambers because they're cheaper than 3 chambers. The 2 chamber was never designed as a street muffler, it was a performance muffler for street/strip or race applications. There is a long back history to this which I won't dig into here, but I can tell you our typical calls were always something like "what's your best flowing muffler?"

OK, I'll give a short history so that the rest makes sense. WAY back when, Cyclone came up with a fantastic marketing plan. The idea was basically, if you have a 750 cfm carb, then you need two mufflers that can (combined) flow 750 cfm too or they'll be "restrictive". The problem is, an exhaust system flows EXHAUST not AIR, so any cfm rating for a muffler means nothing. They used to love putting Flowmasters on a flow bench and then showing how "restrictive" they (supposedly) are because they don't flow a steady stream of air well - which of course they aren't supposed to do in the first place. Exhaust is PULSES rather than a steady state stream as a flow bench measures. Feel the exhaust coming out of any old muscle car with a lumpy cam and you'll feel those individual pulses slapping at your hand. That's simply the nature of an engine with valves that cycle. That same car with a lumpy cam will also have a shaking needle if you connect a vacuum gauge because again, the opening and closing of the valves causes pulsing in the intake manifold. The "smaller" the cam, the less noticeable it is, and vice versa. This is also why intake manifold designers tune for harmonic waves.

So, back to exhaust pulses. Each time an exhaust valve opens, the piston is moving up, pushing the exhaust out of the cylinder. That pulse is actually a high pressure "wave" which is pulling behind it the spent exhaust gasses, so there are two parts to an exhaust pulse. As that pulse travels down the exhaust system it's bleeding off heat/energy, slowing down, and contracting. This is why most stock exhaust systems start off with larger pipes and then go to a smaller size part way through the system - to help maintain velocity by reducing pipe diameter. The other thing that no one ever talks about is ambient air pressure. Don't forget that there is always 14.7 psi of ambient air pressure (at sea level) trying to equalize pressure (force it's way back up the tailpipe) - this is true "backpressure".

Back to other mufflers. Almost all mufflers use some sort of packing material to try to absorb some of that high pressure wave. The only way to do that is to somehow perforate/louver the pipe the pulse is flowing through to then disperse that energy into the packing. Turbo mufflers, glass packs, etc. all work this way as do almost all factory designs. The type and quality of the packing material determines how long it lasts - and obviously, as it goes away there is less sound absorbtion. That is the nature of that type of design and construction.

Flowmasters are chambered mufflers with no packing. They work using frequency tuning - just like bringing 2 tuning forks together cancels out the sound. Flowmasters use "deflectors" (the V shaped part that the pulses are aimed at) and collectors (the V shaped part facing the opposite direction) to reproduce the tuning fork idea but with no moving/vibrating parts. The moving parts are the pulses themselves. This is why I say they're designed to flow exhaust rather than steady state airflow. Case volume (muffler size) is also important. If a case is too small for the application the muffler will be "overpowered" (it will be restrictive in other words) - similar to using stock speakers with a high powered amplifier - you can pump all that power through the speakers but it won't sound good.

Case volume is also important for another reason: In a Flowmaster, when the exhaust pulse hits the "deflector", it splits in two and that creates a low pressure area at the nose of the deflector which the next exhaust pulse then rushes in to try to fill - high pressure will always move to fill low pressure. In this way a Flowmaster will help to scavenge exhaust from the engine. Here is the key difference between Flowmasters and other mufflers - the more pulses you put through a SINGLE muffler (assuming correct case volume) the harder the Flowmaster will scavenge the engine - 8 pulses through one muffler produces more scavenging than 4 pulses through each of a pair of mufflers. It took some doing, but when we got racers to start using the D-port Y collectors and mufflers (paired with the correct type of cam) like the 65020-14 (6" thick case, 14" wide, 5" in and out) they found that not only did they beat sound requirements but they made more torque and horsepower over a wider RPM range. By correct type of cam, let me explain. Prior to Flowmaster scavenging exhaust technology, racers would try to use cam timing "overlap" to improve cylinder filling. Running a narrow lobe center cam (say 102 degrees) would use the trailing end of the exiting exhaust pulse to draw more fuel/air mixture into the cylinder during valve overlap. With a Flowmaster, that lobe separation needed to be widened (maybe to 108 degrees or more) because the Flowmasters would effectively "over scavenge" the cylinder and draw part of the fuel/air mixture right through the cylinder and into the exhaust - resulting in reduced power. That of course was usually blamed on "back pressure" because of lack of understanding. The extreme version of this was alcohol engines where in one case a racer called me and said that at night the fans said they could see "seething" inside the glowing mufflers on his sprint car and that it was burning anything close to it. He got a new cam and a special muffler made for alcohol fueled engines and the problem was solved.

Resonance: As noted above, a Helmholtz tuning chamber is part of a "3 chamber" muffler (sometimes 2 separate chambers, sometimes a single chamber but with 2 different size openings) and is designed to reduce/eliminate resonant frequencies.

As for a street exhaust system, there will always be compromises. The thing to keep in mind is that "street" engines operate something like 99.99% of the time at low to part throttle - unless you drive like a total squid but that's a self-solving problem. So tuning a street system for peak power means that you probably won't like it much for the other 99.99% of the time you'll be driving the car. Dual 2 1/4" pipes will typically handle about 325 crank hp from an engine in the 340/350/360 cubic inch range - again for street use. Dual 2.5" is good to about 400-425 hp for the same size - again this would be for real street use, as in a daily driver car. If you went to say a 450 hp 383, you "might" want to go 3" for the first half of the system, then reduce to 2 1/2" from there back, but that would start to become a street/strip type of sound level.

I don't know what you plan for power output or what you expect to do about headers. Actually, not even sure if you're a crossfire/L98/LT1 car. Here is what I'm putting together for mine: The car is a 91, so it's currently a TPI car. I hope to get it to about 375 crank hp and still pass visual and tailpipe emissions. I'm looking at a mild Lunati Voodoo cam (.515/.530 lift) aftermarket Vortec type heads, and an LT1 intake manifold conversion so that I can use the upper end the cam and heads will supply. I've bought a set of Pacesetter LT1 shorty headers which I'll modify to add EGR and have ceramic coated (did this before on my previous 91), and also a set of LT1 downpipes with cats. I cut the LT1 resonator off so I can use the stock forward pipes and will connect those to a very nicely made 2.5" x-pipe that I bought from Summit. The x-pipe is designed for a 2010-2015 Camaro but it lines up perfectly with the forward pipes from the LT1 setup. From there I'll have 2 1/2" pipes going back to.....Flowmasters of course. The trick here is that I'm using their 5" thick "SUV" mufflers - part number 52555. They're 2 1/2" center/center with a 17" long case. These have a large, dual inlet Helmholtz chamber and should give stock/near stock sound levels inside the car. I've removed the spare tire and will locate the mufflers on a 45 degree angle since they're a little too long to fit in the normal position. The system will end with factory LT1 tips that are modified to accept 2 1/2" pipes - from the factory they are only 2". I'm also going to heat wrap the pipes from the header flange to the point where they split under the rear leaf spring. This will help to keep heat in the system and improve velocity.

Sorry for the long read, but hopefully I made sense and gave you some understanding of my knowledge and opinion on the subject.