INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Looking for help with exhaust gas accoustical questions

Looking for help with exhaust gas accoustical questions

(OP)
I have a muffler that I have built for a a sport boat. Problem is, it works to well. The boat is way to quiet. Some how I think i have actually got the dimensions correct to cancel out most of the desirable exhaust note. I have look around and cannot find anywher to get any answer on what I should change. I though that maybe someone here might know.
It is a v8 engine and the exhaust goes into a 6" dia tube that is 3 ft long that is mounted accross the transom of the boat. It has two inlets that are 4" in dia and are 28" apart c to c. The oultlets are 4" dia alos and are centerd on the tube and are 12" apart.They are all fluch mounted. Have I fluked out and got the distancese so that the exhaust waves are colliding and cancelling each other out? I can shorten the inlet ends of the tube 2" and the outlets 4" if needed. Or I can add length also.

Mark

RE: Looking for help with exhaust gas accoustical questions

So what's the problem. Most boats make way too much NOISE as built.

Figure out what you did right, market it and sell it!!

RE: Looking for help with exhaust gas accoustical questions

(OP)
Yes I would agree, It seems as though the correct sound and the amount of it is just as important as the look of the boat.
From what I can tell it is the equal distance from the inlets and teh distance between the oulets that are the reason.

RE: Looking for help with exhaust gas accoustical questions

What do you do about the heat radiated from the muffler?

Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for help with exhaust gas accoustical questions

(OP)
It is a wet system so there is an amount of water flowing through it.

RE: Looking for help with exhaust gas accoustical questions

Ah. The way that the water flows, and pools, can have a major effect on the way the muffler works. Wet mufflers, on the inside, tend to look very different from dry mufflers.

A drawing, showing the interior details as well as the connections, might help us better understand your problem.

Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for help with exhaust gas accoustical questions

(OP)
here is a very crude drawing. The inside is completely open. The inlets and the outlets are flush mounted. I know that by moving the outlet tubes toward each other the noise increases. In this application I am not able to do that though. If in the center is where the wave fronts collide and cancel then I could weld another smaller tube from the center out and make a U turn to exit at the same point as the outlets on the inside?

RE: Looking for help with exhaust gas accoustical questions

There's a fair chance that the exhaust is unusually quiet because it's flooded. That would not be good for the engine.



Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for help with exhaust gas accoustical questions

At the exact centre, waves at all frequencies will reinforce. But that's not generally where you would be measuring radiated noise. In the far field, the superposition of waves will depend on their wavelengths and the distances from the source of the measurement location. ach frequency will superimpose differently because of the different wavelength. If the sources are nearly coincident, they will act as a single source with double the amplitude.

- Steve

RE: Looking for help with exhaust gas accoustical questions

(OP)
I would agree although because to the sound sources supply the pulse wave at 180 deg intervals would it not not cancel instead of reinforce?

RE: Looking for help with exhaust gas accoustical questions

(OP)
For some reason the picture ended up upside down. So the exs yube does not flood although it does have water through out it. The risers from the headers on the engine are much higher and the outlets are lower that the inlets by at least 2 ".

RE: Looking for help with exhaust gas accoustical questions

L/R combustion events are not normally simultaneous, so acoustic cancellation doesn't really seem to fit for me.

Maybe you've got some kind of cavity resonance, or anti-resonance, going there, but it's hard to evaluate, since we have no data on the gas flow, the water flow, the noise vs. rpm, the system geometry in 3D, etc.


Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for help with exhaust gas accoustical questions

(OP)
I see. On this v8 engine the cylinders fire one cylinder on one side then fire one on the other and so on. The frequency or rpm shouldn't matter if I have 180 deg out of phase waves colliding. I guess what I am asking is this plausible? If so what can I do to change it to 1. verify what is happening 2. change it to achieve my desired effect.

RE: Looking for help with exhaust gas accoustical questions

That's a very unusual firing order.

Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for help with exhaust gas accoustical questions

(OP)
Nope that is the GM LS firing order. 18726543
1 2
3 4
5 6
7 8

RE: Looking for help with exhaust gas accoustical questions

... which puts 3,1 and 2,6 firing in sequence.

Mike Halloran
Pembroke Pines, FL, USA

RE: Looking for help with exhaust gas accoustical questions

(OP)
Ah I see your point. I knew about 2,6 but didn't think about 1,3. So I guess I should drop that train of thought.

RE: Looking for help with exhaust gas accoustical questions

(OP)
I am going to try a little experiment. I am going instal a third ex outlet in the middle between the two others. I should be interesting if it makes alot of difference when I either plug it or leave it open.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close