Exhaust help and ideas

johnny gtir

johnny gtir

Well-Known Member
Been thinking any input would be great seein dannys thread made me ask

After a side exit 3 inch system inc stainless manifold 3"elbow and the massive gains it gave lots of testing and even fitting a second small box on i could feel the difference i want my system for my second R to be the same but less db for the odd track.

Not really interested in full system with say 2 boxes in
ideas so far twin pipes but back into single box at the end similar to bmw
twin pipe twin exit goin off similar idea off dd"s car skyline system
main idea i had which i really want opinions on is a 3" system which goes into a y piece which goes through a big rear box like standard but 3inch entry and a valve similar to skyline when it gets to say 3500 rpm opens and bypasses rear box the valve could work off ecu or even simpler pressure. Hence it would be quiet into my estate on track static only noise level etc. ?
 
red reading

red reading

Active Member
Johnny, my system is 3.5 inch to a "y" piece under the car to 3" twin pipes, they then have v bands so I can change silencers easily on the end which come up either side of my rear diffuser , the silencers are akrapovic turbo bike 60mm internal bore and the car is very quiet now but I can put anything I like on now and have no power restrictions.....time to run e85 and 2.5 bar of boost I think!!!
 
johnny gtir

johnny gtir

Well-Known Member
Very good sounds interesting would like to see that should work a treat. i am going for switchable map ecu so we did think if i have a single 3inch system mess about with two different boxes and just fit one for most the time and the other for track. I was trying to think of suggestions of say a pressure valve like i say stupid things like getting in and out the estate quiet but no restriction when you floor it. Think i am right in saying some skylines have something similar
 
red reading

red reading

Active Member
Why not build a system that meets all the requirement and that is as quiet as possible, you will struggle getting a 3" single system below 100db, as I have been finding out.....so many things vary exhaust noise....I have seen many track cars now running twin exit systems as the reduced bore on them helps reduce noise.....also if you have them pointing in differant directions it helps a lot with static noise tests as they can only test one exhaust at a time not both together.
 
fubar andy

fubar andy

Moderator & N/W Rep
Staff member
Mine is a 3" system, rear exit however and only puts out 92db's on trackdays

When at WOT it's louder and all I had made was a large centre section where CAT used to live and a long sausage baffle after that.

My only suggestion would be as mentioned and have a custom flap system made to keep it quiet when at cruise and open at WOT.
 
PobodY

PobodY

Moderators
Staff member
I'm sure there must be a way to disrupt the standing wave in an exhaust, and thereby reduce the noise. - I was thinking about playing with creating a vortex.
 
PobodY

PobodY

Moderators
Staff member
I can honest say that your old 2.5" exhaust is not more quiet that Andy's 3" system. - When we were at Bedford the dB figures were almost identical.

Part of the problem with having two exits is that you get a resonance between them. By slightly blocking one side the exhaust is noticeably quieter; that's why I was thinking about ways to disrupt the wave. - I figured a vortex is the quickest way to clear the gas flow from a pipe without generating resonance... but maybe that kind of theory is best run past Ed first; I suspect he may know something about the fluid motion of gasses.
 
vss irvine

vss irvine

Well-Known Member
PobodY said:
Part of the problem with having two exits is that you get a resonance between them. By slightly blocking one side the exhaust is noticeably quieter; that's why I was thinking about ways to disrupt the wave. - I figured a vortex is the quickest way to clear the gas flow from a pipe without generating resonance... but maybe that kind of theory is best run past Ed first; I suspect he may know something about the fluid motion of gasses.
Click to expand...
 
johnny gtir

johnny gtir

Well-Known Member
Dont get me wrong here just saying tho even 1 box i could feel the difference in performance again the 3" was way way better just as always i want absolute best of both pref without having to add or remove a box if it was only for track days not that i do many but entering estate early hours etc without having to get out and fit a bung etc
 
PobodY

PobodY

Moderators
Staff member
Makaveli_se7en said:
Like this?: http://www.freepatentsonline.com/6786037.pdf
Click to expand...
Er... yes? - Clearly we're not talking about a jet engine here, but just looking at the field suggests that I might be on to something with regards to having non-uniform exhaust outlets.
Maybe just a cone-shaped insert somewhere would not dramatically change the flow, but drastically change the noise? - That's probably easier than my original idea (a plate of metal, cut and bent into blades to generate a vortex).
 
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