RazMan
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| posted on 10/9/07 at 09:12 AM |
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Middy style Exhaust Design
I'm really not happy with the sound of my V6 exhaust system. I know its never going to sound like a V8 but it sounds so raspy in the upper rev
range that it really irritates me.
So what can I do? I've been thinking of a centre fed silencer with a tailpipe at each end (similar to the MR2), but what about the internal
design? How do I make sure its not going to sound like a fart in a can?
[Edited on 10-9-07 by RazMan]
 
Rescued attachment Exhaust Diagram.jpg
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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worX
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| posted on 10/9/07 at 10:34 AM |
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I'm afraid I don't know anything about exhaust design - but I would of thought a good start to a deeper not would be to alter the size of
the silencer box?
It would be easy enough to knock up a couple of (drastically) different sizes to test?
Steve
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Fred W B
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| posted on 10/9/07 at 11:07 AM |
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Hi Raz
I may be wrong, but I think that to get any sort of "beat" you want to run two completely seperate exhausts, one from each bank?
Cheers
Fred W B
[Edited on 10/9/07 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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jambojeef
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| posted on 10/9/07 at 03:24 PM |
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Its also got a great deal to do with the plane of the crank.
You might never get a typically "v" noise from that engine.
If you want to make it burbley, find out the firing order and separate every other cylinder off into 2 separate silencers each with its own
tailpipe.
The jag v12s ran separate banks which never siamesed and just sounded smooth - no rover v8 warble.
My old cossie v6 was very burbley and I did nothing to the exhaust just removed the resonator box from the intake system.
Geoff
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v8kid
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| posted on 10/9/07 at 03:39 PM |
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the pipe layout makes quite a difference to the torque curve. I had a ballance pipe on my v8 in the last car and the same engine but without a
ballance pipe (no room in a midi) lacks low down torque to the extent that its quite difficult to take off.
Donno how you do it with a v6 though - have you tried searching capri sites?
Cheers
David
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RazMan
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| posted on 10/9/07 at 05:03 PM |
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The front engined V6 cars mostly seem to go for separate banks running front to back with a balance pipe somewhere in the middle. Apparently the
balance pipe makes quite a difference to the sound and torque curve - even the shape of the balance pipe is important. H, X or Y shaped balance pipes
all have their own characteristic effects.
Then there is the choice of straight through or chambered silencers, each having their own characteristics too.
Hmmm .... this exhaust lark is more complicated than I thought 
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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DIY Si
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| posted on 11/9/07 at 04:07 PM |
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Since I can't remember just how much space there is under your rear clam, would it be possible to run two flat(ish) silencers, one for each
bank? Then have one exiting at each rear corner? As for the silencers, I've always used straight through jobbies, but I'm not too fussed
about noise levels, just noise type.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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RazMan
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| posted on 11/9/07 at 04:29 PM |
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Hi Si, Yep, I am thinking on similar lines now. I had a poke around the US Contour forums and apparently they are getting ~15 bhp gain by going for a
true dual system - two of everything. This setup will probably make a more burbly sound although it can still get quite raspy in the upper rev
range.
I wonder if there is any difference in having the silencer closer to either end (i.e. next to headers or tail pipe.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Lippoman
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| posted on 11/9/07 at 06:14 PM |
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Generally, a can near the tail end dampens the sound more than the same one closer to the engine (less volume of gas to handle due to lower
temperatures).
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gttman
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| posted on 11/9/07 at 06:44 PM |
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2 totally separate exhausts is the way IMO... that certainly what I intend to do with mine.
don't bother with a balance pipe for now again IMO.
Andygtt
Please redefine your limits
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mark chandler
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| posted on 11/9/07 at 10:31 PM |
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No no no, you need a balance pipe unless you stand directly between the exhaust you will here two 3 cylinder engines, one quiet one loud.
The balance pipe needs to be straight after the collectors and be 2/3rds the diameter of the exhausts at this point if I remember correctly.
V6's toggle between the pipes, V8's sound 'cool' because of the firing order 18436572 or rllrlrrl, the exhausts bounce around.
flat plane crank V8's or lrlrlrlr, that's why high end TVR's sound odd.
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gttman
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| posted on 12/9/07 at 06:59 AM |
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are you suggesting a V6 specifically needs a balance pipe or that you need one on any V?
Do all V6's have the same fireing order?
Andygtt
Please redefine your limits
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DIY Si
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| posted on 12/9/07 at 08:48 PM |
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I would suggest a balance pipe of some type, but the type depends upon what you have space for. It needn't be anything extravagant, and since
IIRC you're a bit handy with a welder, it may be possible to have a bolt in link pipe, so you can change it's size/length to see what
happens and fine tune the noise a little. The shape, be it H or X for separate pipes does apparently make a fair bit of difference, with a linked X
giving a more unusual sound. If you look at the last thread you put up, I think I posted a pic of such a pipe, but it's more of an X shaped
chamber rather than an actual pipe as such.
I think Mark is saying that all V engines would benefit from a balance pipe, to help improve the sound, or you'd just hear two odd sounding
straight 4's, rather than a burbly V8, for example.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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gttman
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| posted on 12/9/07 at 10:02 PM |
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Thing is I know from experience that a balance pipe is not needed for a burbly sound on a V8.
For example Ultimas do not have a balance pipe, I did actually changed the exhaust on mine and added a balance pipe and extra length purelly to reduce
sound which it did a treat. It didn't sound better though.
[Edited on 12/9/07 by gttman]
Andygtt
Please redefine your limits
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mark chandler
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| posted on 28/9/07 at 12:22 AM |
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Indeed.
If the pipes exit together you will not notice much difference but if they exit both sides, ala Jag et al then stand to the left anf you here that
bank above the other.
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Ratman
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| posted on 28/9/07 at 10:17 AM |
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There are a lot of theories about exhaust design. here is a link I found.. http://www.burnsstainless.com/TechArticles/Theory/theory.html
But I am sure there are better ones than this. It does make reference to a book by Phillip H. Smith which I once tracked down in the library. The
problem I had at the time was with a flat 4 engine. To make a traditional 'free flow" design I had to achieve a joining from pipes from
the left to pipes from the right within 30 inches of so, and I didn't have any any space for getting the pipes across from one side to the other
without compromising ground clearance. So I used an "independence" design, which effectively gives each cylinder it's own pipe, and
brings all the pipes together into a single large chamber effectively negating the influence of one cylinder's pulse on the flow from any other
cylinder. Each cylinder simply has it's own tuned resonator. The collector box has to be something like 6 or ten or something times the volume
of one of the cylinders. This worked well for me because I was able to locate this collector behind the transmission and feed pipes to it from both
sides of the engine. It does give a good note too.
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RazMan
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| posted on 28/9/07 at 01:49 PM |
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I have been doing a bit of research (basically asking people who know what they are talking about  ) and although I am getting some conflicting
advice in some areas the expansion box or resonator seems to be a common trend. I am still unsure about the 'dual system' idea on a V6 -
some people say its good and others say it will lose power and sound strange. The main limitation as I see it, is that my engine is a transverse V6
which means that the headers from the front bank has to come under the sump to join the rear bank. Therefore this means that the headers are going to
start off being different lengths - not good from a design point of view, and a true dual system would probably mean lots of plumbing to correct this
flaw.
I am not sure of the actual calculations involved but it is now my intention to keep the existing single silencer and introduce an expansion chamber
into the system. This might be a separate can or in theory it could be included in the existing silencer (about a third of the length) Apparently this
will change the note of the exhaust, making it deeper and hopefully less raspy. See the pic below...
**edit** I have since been told that the expansion chamber needs to be an empty chamber that the gas passes through (no perf tube)
I will be meeting a fellow Locost Builder (who knows about these things ) this weekend to experiment further.
Ratman, have you got any pics? Thanks for the link - I am reading it now 
[Edited on 28-9-07 by RazMan]
 
Rescued attachment Expansion Chamber Idea.jpg
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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