where are the exhaust scientists

George, I wish you would post on this one more or leave the ones you do.

H vs X vs none is something that probably will go on forever. Factory applications aren't there for no reason at all. I like an H pipe up front.
Maybe the engine responds well @ certain Rpm maybe it doesn't and then again maybe different for a different spec engine. Sherman's opinion certainly caries a lot of weight.

Anyhow, that's really not the main point of this thread.


Im just wondering why an x pipe at the rear sounds so damn good and why is it quieter with it than without it.
How it performs would be the topic of another thread and maybe I can swing some chassis dyno time for that one.

 

For sure the x-pipe will reduce the noise level. I usually run one for that reason. Anything that makes it quieter and doesnt actually HURT power works for me. Posted that, then thought, "naw, dont need the BS" and deleted it. Joe wasnt the only one that said this either, this was on Speedtalk, and a couple other guys that I respect and listen closely to (you KNOW there aint many of those!!) said the same thing. I dont have a horse in that race one way or the other, just thought it was interesting.
Joe and the other guys who mentioned it were all pretty serious types, so you can figure their examples were WELL sorted in terms of collector length, primary diameter ect. Maybe they do help crutch a system that isnt as well dialed in, I just thought the comments were interesting.

 

I'll tell you a little secret, theres a LOT of engine related stuff that I think about saying, but zip my lip, and dont post, just because I dont care enough to start a pissing match.

 

Come on man engine secrets aren't like valve stems

 

VALVE STEMS??!! Havent you sold those things YET??

 

Ttt.
Still looking for input.

 

I think you got it early on: having the x pipe close to the rear is canceling out some frequencies, giving a more mellow and pleasing tone. It's probably canceling out some of the higher frequencies or maybe mids. You basically created a noise-canceling muffler.
I'm sure there is some wildly complex formula to explain exactly what is happening and why, but it was just pure luck that you hit a sweet spot. Locating the same pipe in roughly the same location on a different car with a different engine might not give the same sound at all.

 

I think you are exactly correct. Pure blind dumb luck and with a somewhat silly location for an x pipe tried just because .....

Also think your correct here- might sound different with different car, or specs.

But , it could be replicated if the wildly complex formulas could explain and then expand.

 

The science as best I recall...there are nodes...and anti-nodes, for a given frequency of sound. The node length can be a measured distance, and is how organ pipe lengths are established. So certain freqs will "set up" due to pipe/system length. The increase in "dia" did eliminate a resonant freq, when I put a splitter on the tailpipe end of the system. Thanks Vicky for starting a good thread!

 

I'm going try a completely different designed x pipe tomorrow.
Wonder how that's going to be .
Any predictions?

Just the X pipe out of this kit
http://www.gettorq.com/store/media/...fb8d27136e95/p/y/pypes-challenger-exhaust.jpg

 

why mess up a good thing ? just askin.

 

Well its an experiment right.

If I get the same results with a different x style x pipe I'll know that the design has nothing to do with it , but its the cross flow.

If I get different results , I'll know its the design of the pipe.

I spent an hour at the neighborhood exhaust shop talking with the guy there. 30 some odd years doing this stuff. He can't figure out why either but in all of His years he never saw or even thought about a rear x pipe. Majority of cars it would be difficult to do, not impossible but difficult.
He's got a challenger X pipe to try .

 

I have glass packs forward just behind the Trans. I wonder what the difference would be with a h pipe in front or the rear of the mufflers.
Mild 350 with 1.75" pipes exiting out the back.

 

You could try it and see.
H pipe balances the pipes pressure, or sound levels and pulses.
Moving the mufflers back lowers both the decibles and octave.
A h behind the glass packs would probably turn down the big Zipper sound that they make

 

Well, you can add me to the list of "x pipes suck" people. I had some spare time today so got under my car and cut out the X pipe and replaced it with pipes that make my exhaust system a basic "two pipes that are not tied to each other in any way" setup.

It made a very good difference in terms of noise - the car much quieter at all RPM's and there is a big reduction in all the 'buzzy' resonances that were there at idle and cruising conditions. It's a lot easier to talk to someone else in the car now. The exhaust note that is left are the lower tones which are far more pleasant.

If the car is any slower, at all, I can't tell. It actually feels more 'free breathing' without all the resonances. Another benefit is with the two sides separated I could hear a miss which turned out to be a plug wire that had come off a little.

 

So what you are saying is this :
Although I didn't know it was running on 7 cylinders + 1 with a miss with an X pipe, it sounded like shit and now that I've removed the x pipe and fixed the miss, It runs better, breathes free-er & sounds better on all 8 too. Therefore I've concluded X pipe was to blame and they suck.

Brilliant observations but flawed application and conclusions.
What's better ? All 8 and no xpipe or 7 with an x pipe.

 

It is not surprising that results are all-over-the-map. Most folks are running the wrong size exhaust system, totally ignoring any notion of volumetric efficiency, or any hope of the scavenging effect. You still, to this day, hear folks talk about the mythical "back pressure". I guess myth is easier to believe that science.

 

I think Bigfoot started all that back pressure crap.

 

"So what you are saying is this :
Although I didn't know it was running on 7 cylinders + 1 with a miss with an X pipe, it sounded like shit and now that I've removed the x pipe and fixed the miss, It runs better, breathes free-er & sounds better on all 8 too. Therefore I've concluded X pipe was to blame and they suck.

Brilliant observations but flawed application and conclusions.
What's better ? All 8 and no xpipe or 7 with an x pipe. __________________"




Here's the deal, Clyde. I didn't fix the plug wire until AFTER all the comparisons were made. AFTER, see?

Plus, the plug wasn't firing 'never', it just wasn't firing each and every time.

Before, on 7 cylinders, you really couldn't order food idling at a drive in window. AFTER I removed the X-pipe, on 7 cylinders, there is no problem ordering food at a drive in window. See what I'm getting at?

 

Oh yea I've got a Clyde over here for ya! !

Unless you ran all 8 thru the xpipe - just like you ran 7+1missing thru the xpipe- you are not making an even comparison. At times (on the miss) there was 25% less flow thru one side of the x or 33.3% more thru the other , just depends how you want to look at it. That can have plenty to do flow, scavenge, breathing and resonance. ESPECIALLY on an x pipe that uses the other side's pulses to work.

You can draw any conclusion you want from any info you want.
I merely pointed out how it was inconsistent and illogical to come to the conclusion you reached. Xpipes suck. Perhaps they do suck, but not from that info.

 

Ok, let me start by saying I havent done it and I'm a snotty nosed 23 year old kid.

I didn't read the entire thread so this may be repeated, but here is my opinion:

Every set up is different. Every engine, every set of pipes, same brand or not.
That said, You can tune pipes to do different things. In any pipe there are standing waves. By tuning the length for each and every set of pipes, you can get different results. Keep in mind that these waves will change and resonate differently at different rpm's. You can set nodes in certain areas in the pipe that will ampify or cancel eachother out.

Experiment:
-Find something that makes a tone, like a phone with a really loud dail tone.
-Get a tube and cap one end.
-Connect a smaller tube and small jug for water to the bottom.
-Hold jug about half way up the pipe and fill one end with water(they will both fill to the same level of course)
-Now put the buzzer above the end of the pipe and move your jug to different heights and listen to what happens as the water level changes.

You will notice quiet and loud spots. This is because the standing waves either "add together" or "cancel". This is why some pipes have that powerful pulsing sound and why others are mellow.... even the same setups on different cars. A half inch in lenght can make all the difference! Things get more complicated when you add multiple pipes and hot exhaust gas(speed of sound changes with temperature).

Another thing is the "feeling". That has to do with pitch or frequency. Humans only hear a narrow set of frequencies. Take a dog whistle as an example... just sound like blowing through a straw. The ground pounding you speek of (although hard to understand because I'm not you) could be a couple things. It could be that the frequency makes something you are sitting or standing on vibrate at its resonant frequency. An example of this is when a piston airplane flies over your house and one of you windows or a section of wall vibrates. Or that the ground itself is vibrating and yes it happens.... just drop something really heavy on the ground.

The other feeling, the one in your body, can be caused by certain frequencies that you cannot hear. There are a few low frequencies that irritate the body, even cause pain or nausea. Just borrow a gangster kids sub woofer and a "bass testing cd"
You will feel the "ground pounding". You can change the frequency of the exaust note by changing the diameter of pipe. Another thing is the rpm. The ground pound may happen in segments of the rpm band and not in others.

What it boils down to is you are gonna have to tune the length and diameter of the pipe for each set-up for 'max ground pound' and 'least volume'. That has nothing do do with power or flow. H-pipe placement basically complicates things further by adding a reservoir and more pulses. Usually resulting in less resonance.

Tuning for sound and power are very different, but achieved using the same principles. And as a side note, two stroke pipes rely less on sound waves and more on creating vacuum by expanding the hot gasses... different ball of wax.

I'm sure there are some typo's but im not reading that haha.