where are the exhaust scientists

Here's the thread :

http://www.jalopyjournal.com/forum/showthread.php?t=723322

The following is what I found , anyone care to explain the findings. Perhaps theories or opinions. Thanks


Update

Well I got my small cube (307), high compression 10.5 :1, XE 262 cam fired up.
After the break in and tune I started messing with the exhaust.
First is long tube headers into 2.25 pipes, H pipe about 24" back. That all stayed.
This is mandrel bends no bends over 22.5 * 4 per side and those were used as offsets with about 24" between bends.

I started with summit turbos and then purple hornies louvers open toward the engine at the very end for resonators with a 12" tail pipe at the bumper. Very nice sound, mom wouldn't mind driving it and the neighborhood would know any different.

Next I turned the purple horneys around and that didn't make much difference but it was a touch louder.

Next took the PHs off and swapped in a straight pipe. Didn't care for that sound much so I didn't mess around much.

Next I took the turbos off, swapped in the PH and piped it back to the bumper. Louvers open to engine. Now were getting somewhere but has that glasspack sound at acceleration. Sounds like a really big zipper .

Turned the PH around and that made it worse.

Next I put the PH back at the end with 12 inch tailpipe. That sounded much better and started thumping some. Much lower note and a smaller zipper.

Next turn the PHs around and the zipper got bigger . Some high pitch sound came thru that sort of annoyed me.

Not much left so tried no mufflers, just 12 feet of pipe. That sounded pretty good but rough. Thumping pretty good but kind of too abrasive. It be fun for couple miles not couple hundred

So at this point I'm thinking the very first way would be best but no pounding..

Over in the corner I had a 2.5" bassani x pipe. I re finagled the pipes and put it at the very end with 12" tailpipe. Now that sounded good. Took away the obscenity of open pipes. Thumping like a freight train going by but we could talk at normal conversation right at the bumper.
Quiet as can be at the front but massive low rumbles out the back. Throttle was perfect sound level. Mom wouldn't mind driving it but people would be looking at her funny. Neighborhood would know you are leaving but not wake up the baby.

I'm pretty happy and think any hotrodder would be it sounds like it means business and to quote my buddy " beast"

I'm not sure why the "X" pipe made such a difference placed at the very end of the system.

 

Exhaust is actually sound waves. Think of 4 guys with old Trumpets standing 20 feet apart blowing the same notes in the same direction. It sounds pretty tinny and raspy. Now move them 2 feet apart doing the same thing. Now it sounds kind of like they are actually trying to make music. Now take them and make a square with them pointing there horns at the center. Now you have a melody, kind of the same with the X pipe. The sound waves are mixing as they cross over. There is a reason the Philharmonic Orcharstra plays in a symphony hall and not a Gymnasium and why a Marching Band sounds better inside than outside.
The Wizzard

 

the common train of thought is to put the X pipe as close to the engine is possible.
this is for flow and scavaging purposes of the exhaust pulses.

I've heard that colliding sound waves the same frequency but opposite can cancel each other out. it's quite apparent from this little experiment that's true. I'm sure there's all sorts of sound waves being cancelled by random selection in the x pipe located at the very end of the system

I wonder how the X at the end of the system would effect the flow. Colliding pulses can stop each other. They are cooled off and slower by the time they get back there. Maybe nothing here to look at, maybe there is?

 

From all my test and toys, the X smooths out the sound simply because you can now hear all 8 cylinders out of each pipe. Gives the engine sort of that high tech 16 cylinder sound. That alone seems to fool the brain into thinking the sound level is way lower when in fact, measurements show it may only be a dB or two (at ten feet) lower.
I think that far back, all the engine may see is that you have now added another couple of bends which makes the engine see the pipes as relatively longer.

Tom

 

I've learned over the years there is quite a bit of tecnology in finding horse power in exhaust. I understand a little more than some and if I were a younger man it would become an income for me. I have enjoyed building headers and exhaust systems by hand.
The Wizzard

 

Bump for the day crew

 

FWIW, a guy who I have a great deal of respect for, always told me to spray some paint on the exhaust pipes from the headers to about halfway back. Run the engine long enough to get the engine thoroughly warmed up, and then look at where the paint stopped being affected by the heat, and put the crossover there. I do not know the science behind it, but it gives you something to think on.

 

Well I am going to use the wrong words here but that is where the pulse stope and begines to travel back toward the exhaust valve, or at least that is what I have been told.

They have made big inroads with dyno tunning and have discoverd that the burnt off paint theory really doesn't work so well, at least for discovering collector length. An old trick was to run your collector long and run the car at the rpm it was designed to run at then cut the collector where the paint burned off. They since have discovered through dyno tests that it is only a ball park and normally the collector needs to be longer than that.

As far as the cross at the end of the pipes I believe that it is just canceling itself out much like the theory behind a suit case muffler. I can't say if it helps or hurts the performance but if it makes it sound good and that is what one is after I am all for it.

The Ol man used to like a straight pipe with a resonator at the end, I grew up to that sound so that sounds good to me. Everyone has their personal likes and dislikes I suppose.

 

Yes, I've done that for collector length. However the transmission and H cross over can't occupy the same space, dropping it below the trans wouldn't work so it went in as close as possible which is just after the cross member. Probably could have moved it 6 " forward in front of the crossmember but that would have made some things impossible to work on.

"Headers by ed" has a great explanation of what you speak of on his web site. Also some pretty good info on simple venturi cone collectors. He also thinks there may be some benefits for the cones with full exhaust.

 

Allow me to share what I've learned over the years, 31.

Ready? Here goes. "_______________________________"

And that's it in a nutshell.

Lol. Seriously, I'm glad you're still investigating the "shake the ground" issue.
Interesting stuff, 'cause the exhaust note has so much to do with the persona of a car.
We may eventually actually learn more about this, if enough guys pay attention.

Hey everybody...anytime you can, if you hear a really thumpin' car that shakes the ground, ask the owner about his setup...especially the particular engine, compression rating, cam, and exhaust configuration used. Then share it with us on one of 31's threads here. Maybe we can actually get this down to a science. And then we can all "shake the ground".

 

31Vic,
I have heard from other header sources that venturi cones work well even with full exhaust so headers by ed is not alone in his thinking.

Here is a trick to mellow a raspy exhaust as well. The good old balogna slice. I don't know how it works but I do know that it will take the bark right out of a set of pipes.

 

I probably can't add much since I really like the sound of the Speed Sport roadster at full song.

 

There's a lot of science to this stuff for sure.
Did you know they have been working on electronic muffling systems? They use a speaker to produce an equal and opposite sound wave and that effectively cancels out the sound. Full flow, no sound. Electronics are expencive but they can quiet down some really noisy crap.


What else I found was that the majority of sound level was coming from the summit turbo mufflers them selves. It was Loudest right there and causing lots of racket in the cockpit right behind the seats. Didn't care for the tailpipe note on them alone, and the PH as resonators made it real quiet but the mufflers were still noisy.

 

I got elcheapo short turbo mufflers behind the low volumn small block in my willys, it is quiet in the cab but behind it sounds like long straight pipes. As long as you are not standing on it it is fine. Maybe the difference in the cab is truck bed over body shell. The trunk area on a coupe is going to work like a big echo chamber.

Maybe the key is to put some sound deadener in the trunk, ever if it is just some old blankets.

 

Your saying the Turbo muff's increased the sound level?

 

This won't teach us much, except maybe what not to do. But just for the hell of it...

I had an OT late '60s stepside Chevy truck years back. Way lowered, SBC with a pretty thumpy cam, no carpet, headers and only some "Hush Thrush" mufflers. No tailpipes at all...so the exhaust exited right under the cab. Oh...my...god. Heading down the highway, the sound in the cab was absolutely deafening. Turned the whole cab into a resonating sound chamber. Really rattled my brain. Way too much...lol.

 

No, let me clear that up, sorry
I'm saying that the majority of sound was coming from the muffler itself.
By the engine you hear the whir of the machinery, by the tailpipes you hear blup blup blup, but by the muffler you heard all sorts racket. It was loudest at the muffler and not nice to listen too.
Might just be the 20.00 muffler

No mufflers and just the x pipe at the end was very quiet in the cockpit, quieter that the turbos in the cockpit but over all a bit louder in the building with out the turbos. Also pounding the ground without the turbos. However since the racket generating from the turbo muffler was not there it sounded much better.

 

.
I ran the same setup in the same truck [only with a 292 six, 6 into 2 headers . I eventually had over-the-axle tailpipes made up for it that ended in 3 inch chromed, balony-cut "bluey cans". Sounded like a million bucks with a deep throated roar..no harsh rapping sound at all. Loved it to death!

 

Interesting observation, and makes sense. I will keep it in mind when I finish my trunk.

 

I usually run a !/2" larger diameter tail pipe than the rest of the system. Seems to give more thump, less rap. Even the tip dia. makes a difference. My stude has three inch dumps with an angled tip that can rotate. If pointed at the ground it's noticeably louder. (kicks up too much dust! Pisses off the street rodders!)

 

Have you done much with Flow Masters? I ended up with them on my 51 after 2 different cheep sets and found a big difference in performance. However I do not have any tailpipes yet (talk about Rumble inside) . Before the Flow Masters the motor labored to R.P.M. With the change, not so.
The Wizzard

 

Wizzard,
Those old suitcase mufflers are a technical marvel aren't they? The design (decades in the making) actually promotes scavenging.

 

No explanation, but a story. NASCAR used to hold road races at the old Riverside Raceway in the '60s. Watching from the S's, when the field went past on the first lap and were still bunched close together, the ground would shake even though we were probably more than 100 feet from the track. Impressive.

 

Somewhere here in my books is one titled: "The scientific design of intake and exhaust systems" - I think it's one of the Terry and Baker series. If I can find it, it might have some answers

 

I was told a crosspipe could affect the engines torque?

Close to the engine would give the engine maxtorque at a higher RPM, and in the back/ end of the exhaustsystem would help for a higher torque at low RPM

Are these thoughts only bullshit?

 

Some of you on the Hamb have heard my exhaust on my '40 Chevy Coupe.
It is an inline six, but when idleling, it sounds like a big block.
There is a formula and it has to do with several things.

1. Open breathing. (Mine is ported & polished. needs to scavenge exhaust)
2. Dia. of pipes all the way through. (must get bigger as you go back)
3. Open chambered mufflers (low restriction)
4. Muffler position (the closer to the motor, the deeper the sound)
5. Stroke of piston. ( the longer the stroke, more air&fuel, the longer the sound wave)

Longer sound waves and larger diameter pipes, the deeper the rumble.

See attached image. Header pipe sound waves are closer together (higher pitch)
With a open chambered muffler, the sound wave will not be interrupted and will "Flow" better. Larger dia. exhaust tubing and longer after the muffler, will lenghten sound wave.
At the end, before exiting pipes, give it an extra tall area to resonate then exit.
I have 6" tips on mine but a 3.5"-4" tip will work too.

 

Keep in mind here that exhaust tuning for performance and exhaust tuning for sound are two different things. Quality sound doesn't always correlate to best power. There is a hundred years of history on ways to make power with exhaust. Automakers have only been using acoustic simulation software to fine tine engine sound for a decade or two. They are getting fairly suceesful with this, the 5.0L Mustang and Dodge hemi pickups being good examples. This type of "science" is not within our reach, so the type of trial and error that is being discussed here is probably the best way to get the sound you want.

 

You said it P-n-B'r They have made a believer out of me.
The Wizzard

 

And with all the R&D , magazine articles, mega buck studies OEM research- not one mentions an X pipe at the rear.

Just to make sure I wasn't imagining things, I experimented some more.
I moved the X pipe closer to the engine with no mufflers - 2 feet, 4 feet, and 6' so that's a total of 4 places.
I had a couple buddies over and got their opinions while I repeated the experiments.
Unanimous - turbos sound like crap in 2 different locations
Unanimous- turbos and PH too quiet.
50/50 on rear mounted PH like vs dislike
25/75 on front mounted PH like vs dislike
Unanimous - no mufflers too obnoxious for DD but sounds good.
Unanimous - X pipe forward 6' no mufflers sounds just like no mufflers
Unanimous - X pipe forward 4' no mufflers still sounds like no mufflers but less Rap.
Unanimous - X pipe forward 2' sounds better but some Rap on the throttle. 50/50 on the like
Unanimous - X pipe at the rear sounds the best, no rap and conversation QUIET.
One guy said it made his balls tickle but he's got issues Lmao. But it pounds hardest.

Just to confirm quite, I started my 103 inch Harley with Rinehart pipes and you could clearly hear the bike over the SBC with no mufflers. We could talk normally by the bumper but not by the bike. A rev on bike got some wincing and a rev on the v8 didn't, it was loud but not piercing.

Kind of a neat experiment, wish I had a chassis dyno to do this on.
And just because it was there , otherwise I wouldn't have been able to do it.
That bassani X pipe is a bit different compared to others on the market too.

 

You need to look at the firing order of the engine to appreciate the purpose of the x pipe. A very common firing order is 1-8-4-3-6-5-7-2. Now look at just the left exhaust as the engine goes through the firing order:
Fire - nothing - nothing - Fire - nothing - Fire - Fire - nothing
So the exhaust "flow" not only consists of pressure pulses they are also unevenly spaced creating a very turbulent flow instead of anything approaching a much more desired laminar flow, by the way which is much more efficient. It turns out the times of high pressure on the left bank are precisely at the same time as the low pressure is on the right bank. Therefor the reason for the X pipe is to vent of the high pressures from one bank to fill in the low pressures on the opposite bank, smoothing the flow of both banks. Obviously, the closer to the engine, the more benefit there is to be gained.
Ford, for one, used cross over pipes on their dual exhaust starting in the early 60s, while not as efficient as an X pipe (gas doesn't flow around sharp bends as well as curves) it still worked. Carroll Shelby stated that the cross over pipe just behind the collectors on the 306 HP Shelby Mustang GT-350 by itself added over 10 HP over an identical system without the cross over.
Plus the car will sound better, especially when listening from one side. Which would you rather have:
BLAT - ..... - ..... - BLAT - ..... - BLAT - BLAT - .....
or
BLAT - blat - blat - BLAT - blat - BLAT - BLAT - blat

Cheers!