v8kid
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| posted on 22/1/08 at 01:26 PM |
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Midi Exhausts
Chaps I'm posting this here as it is an issue common to us.
My exhaust needs a tuned lencth of around 30" primary plus 30" tailpipe which is challenging but possible if the silencer is included in
the tailpipe.
However the tuning book I'm using states the tailpipe tuned length stops at the start of the silencer. How come I wonder?
After all the silencer is just a straight pipe with perforations round it! Could it be that the silencer absorbs the pulse waves or that the volume of
the silencer acts as if it was the open air and causes a premature reflection?
Either way it is damn near impossible to package a total length of 60" of pipe plus 20" of silencer.
Currently I am running with 20" primaries and 12" tailpipe before the silencer and there is a distinct lack of torque.
How did you guys overcome the packaging problem?
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Howlor
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| posted on 22/1/08 at 01:44 PM |
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Can you ask me one on sport please?! 
Sorry no help I know but hope you get an answer.
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kb58
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| posted on 22/1/08 at 02:14 PM |
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quote:
Originally posted by v8kid
...Could it be that the silencer absorbs the pulse waves...
Yes. Tuned exhaust only really works with an open exhaust. It counts on sudden transitions in cross-sectional area of the tubing which serve as
reflection points.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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v8kid
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| posted on 22/1/08 at 03:34 PM |
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KB - Thats my understanding but a straight through silencer should be just that - straight through.
It must be that the perforations in the silencer dilute the sudden change and muck up the reflection.
I wonder should I have an expansion chamber prior to the silencer to get this sudden change?
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thomas4age
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| posted on 22/1/08 at 10:07 PM |
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Nah KB58 not true,
you can shift peak torque RPM through the rev range by altering the primairy length and volume, with tailpipes cats the whole package behind the
collector. so the effect of the hemholtz pulses is still very much alive in any system with equal length headers.
make sure the length of the intake tracts is calculated for the same rpm as the exhaust system
also make sure the firing order and the collector entry order are correct which for a crossplane V8 is not the same as an in line flatplane 4.
grtz Thomas
[Edited on 22/1/08 by thomas4age]
If Lucas made guns, Wars wouldn't start either.
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kb58
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| posted on 22/1/08 at 10:15 PM |
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Huh, I guess I'm getting primary tube resonance mixed up with collector pipe length. Sorry about that!
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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v8kid
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| posted on 23/1/08 at 08:12 AM |
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My understanding is the most powerfull pulse is reflected at the primary junction (4 into 1) but at the tailpipe there is another reflection which
reinforces/cancells the primary reflection albeit at 4 times the frequency and at a lower amplitude.
Is it significant?
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v8kid
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| posted on 23/1/08 at 08:14 AM |
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Max revs 7000 peak power 6500 peak torque 5000 but would like more low down power
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Kaspa
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| posted on 29/1/08 at 06:17 AM |
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an easy fix to this problem i have just found out about as i have a similar problem with a clubman i have just rebuilt,
the answer is an expansion chamber in front of the muffler of equal cc as the engine. that according to the exhaust gods will solve your lack of
torque
Kaspa
understeer= when you hit the wall front first
oversteer=when you hit the wall back first
HP= how fast you hit the wall
Torque= how far the wall moves when you hit it
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v8kid
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| posted on 29/1/08 at 05:23 PM |
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Ah ha! Thats the info I was looking for. By coincidence I found a web site by Dave Vizard advocating an expansion chamber but not specifying the
size.
Do you have any links to your source?
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Kaspa
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| posted on 29/1/08 at 06:05 PM |
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exhaust whoes
Hey mate , check this site and talk to John, a real nice guy who knows his stuff. he is in the process of building me a new system for the race car
that will solve similar problems.
www.hytechexhaust.com.
cheers Kaspa
[Edited on 29/1/08 by Kaspa]
understeer= when you hit the wall front first
oversteer=when you hit the wall back first
HP= how fast you hit the wall
Torque= how far the wall moves when you hit it
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v8kid
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| posted on 30/1/08 at 01:05 PM |
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Ta for the link - way out of my price range I'm afraid. In locost fashion I'm looking to understand the theory and make it myself. Looks
nice stuff though
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Kaspa
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| posted on 31/1/08 at 12:05 AM |
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Hi bloke , cost well not alot really when you consider the gains , we have gone through 3 complete systems on a 3SGE i just built,[ for the beast in
the Avatar] at over a grand each and each one garuanteed it was the ultimate fix, NOT. and when you consider he offers a money back garuantee no bad
value i reckon,
anyway back to expansion chamber, what it dose is simply tells lies to the system, it thinks its an open system with no muffler and all the pulse
waves will then start from there, thers a lot more science to it than that, but thats basicly it in a nut shell, its common on speedway cars were
length is restricted and they have to run a muffler.
the only important thing is chamber volume MUST equal total cyl dispacement or it wont work properly.
are you contemplating building your own system , if so drop me a message and ill give you some important and money saving tips that will help increase
you power etc
cheers Kaspa
[Edited on 31/1/08 by Kaspa]
understeer= when you hit the wall front first
oversteer=when you hit the wall back first
HP= how fast you hit the wall
Torque= how far the wall moves when you hit it
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