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Old 17th June 2007, 17:51   #1
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Question Variable back pressure muffler?

Hi guys, I am reading this book on EVO's .. its called 'EVO-The road car and WRC story'. I found the following para interesting.. "The fitting of a variable back pressure valve in the main muffler provides better noise reduction at low engine speeds and lower back pressure at high speeds." This para was talking about the EVO 7. Few questions, performance wise, is higher back pressure at low rpm and lower back pressure at high rpm better? Can this kind of muffler be fabricated? Idea sounds simple enough, but i'm sure it'll require precision fabrication and tedious calculations right? And if someone can explain how back-pressure (high and low) affects performance, that'll be awesome. Thanks.
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Old 17th June 2007, 18:10   #2
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AutoSpeed - Butterfly Effect

Here is an article which gives an in-depth description on how a similar device works. A controlled butterfly for variable fsound/backpressure, sold by Active Exhaust Systems, Australia.
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Old 17th June 2007, 18:29   #3
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Quote:
Originally Posted by autopsyche View Post
AutoSpeed - Butterfly Effect

Here is an article which gives an in-depth description on how a similar device works. A controlled butterfly for variable fsound/backpressure, sold by Active Exhaust Systems, Australia.
That made for an interesting read!

Are such systems commonly used?
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Old 18th June 2007, 02:23   #4
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Thanks autopsyche.. Excellent link.. But according to the system, doesnt it mean that when the butterfly valve is almost shut, it'll increase back pressure even more than it would have been without it? still wanted to know if.. @ low rpm, high back pressure= better performance? and @ high rpm, low back pressure=better performance?
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Old 18th June 2007, 05:46   #5
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Dude I got variable back pressure system from ANSA on my coupe.. its pretty effective... I can adsjust the tone/presssure with an Allen key depending on Freeway mode or city traffic.. or in between
its not elctrically operated ..
I had posted a review abt it on Superhonda or Hondatech etc ...dont remember which one as it was some time back..
let me pull up some links with pics...

Quote:
Originally Posted by Deepz View Post
Thanks autopsyche.. Excellent link.. But according to the system, doesnt it mean that when the butterfly valve is almost shut, it'll increase back pressure even more than it would have been without it? still wanted to know if.. @ low rpm, high back pressure= better performance? and @ high rpm, low back pressure=better performance?
see if this answers your query...
http://www.team-bhp.com/forum/techni...tml#post413214 ("Dude I bolted on 25 BHP" FAQ !!)

Last edited by chetanhanda : 18th June 2007 at 05:51.
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Old 18th June 2007, 16:45   #6
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that was a nice write up chetanhanda, thanks for the link.. i had to read it 2-3 times.. but it gave a clearer picture..
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Old 21st June 2007, 00:21   #7
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interesting, seems simple enough but the point being is it actually that simple?
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Old 21st June 2007, 08:12   #8
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Quote:
Originally Posted by speed0mania View Post
interesting, seems simple enough but the point being is it actually that simple?
its not simple, I have mentioned that Im trying to make it simple for people to understand... realistically it should be explained by a 500 page technical manual with diagrams.. and tested on a loading type dyno with all the facilities available to a WRC team...
just listing out the basic points and basic theory took 1 page...

why dont you go ahead and explain it the "real way" without making it over simplified ..?
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Old 1st July 2007, 01:57   #9
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Ok Guys here is the Video Of the same setup.I think i am right.



Thans,
Niki.
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Old 1st July 2007, 02:17   #10
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Doesnt the Yamaha R1 EXUP valve work on a similar principle? The EXUP is electronically controlled.
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