Hello all
Has anyone tried different ways of quietening the exhaust without changing the pipes or mufflers?
I have 3" pipes and was thinking of restrictor plates under the carb or in the exhaust.
I already have what i call 'bullets' inside the pipe. they are 2" diameter thick mesh filled with steel wool. They seem to work ok but are still not enough.
Any thoughts on the difference between steel mesh & fibreglass??
Obviously this is all for legal reasons
Thanks
quietening exhaust - without changing pipes or muffler
Started by
_the gts_
, Dec 30 2012 12:34 AM
25 replies to this topic
#2
_434LX_
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Posted 30 December 2012 - 09:52 AM
Stick a couple of ball valves on your tail pipes 
#3
rexy
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Posted 30 December 2012 - 10:05 AM
At the flanged sections you add in thin plates - I made mine from aluminium sheet lying in the shed.
You block as much of the diameter as possible without making the car too poorly running to get to the testing station.
Multiple flanges mean you can add multiple plates.
I found covering half the area of a twin 2.5 inch system (each pipe, one spot each side) prior to the rear muffler took 8db off the noise test result.
Still drove okayish and got the job done.
You block as much of the diameter as possible without making the car too poorly running to get to the testing station.
Multiple flanges mean you can add multiple plates.
I found covering half the area of a twin 2.5 inch system (each pipe, one spot each side) prior to the rear muffler took 8db off the noise test result.
Still drove okayish and got the job done.
#4
_red roar_
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Posted 30 December 2012 - 11:49 AM
Do exactly what Rexy has suggested, works a treatAt the flanged sections you add in thin plates - I made mine from aluminium sheet lying in the shed.
You block as much of the diameter as possible without making the car too poorly running to get to the testing station.
Multiple flanges mean you can add multiple plates.
I found covering half the area of a twin 2.5 inch system (each pipe, one spot each side) prior to the rear muffler took 8db off the noise test result.
Still drove okayish and got the job done.
#5
_shan620_
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Posted 30 December 2012 - 06:50 PM
That's what I done to pass Db test. Get a plate and drill a few holes in it to restrict the flow a bit.
#6
_the gts_
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Posted 30 December 2012 - 07:13 PM
That is pretty much what I have done so far although if you can imagine the plate having something like a coke can in the middle (which is actually mesh) full of steel wool. Do you think fibreglass would be better. The do reduce the noise quite a bit but its still not enough.
Ball valves with actuators on would be ideal Andy, you could tune it, 3" valves from the clave ar a little big though!
Ball valves with actuators on would be ideal Andy, you could tune it, 3" valves from the clave ar a little big though!
#7
rexy
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Posted 30 December 2012 - 09:30 PM
The glasspack type solution you have described is probably less effective than severely restricting the flow as I have described. The effect seems to work better the closer you can get the restriction to the engine end of the system. Maybe you need to add another set of flanges in addition to your current set up to allow you to add more restrictors.
#8
_The Baron_
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Posted 30 December 2012 - 10:05 PM
Rolling up a heap of fly screen wire and shove it up each intermediate pipe before the muffler was an old trick that worked.
#9
_V6 UC_
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Posted 31 December 2012 - 01:43 AM
I also put I piece in between the flange before my diff. Just used a bit of 1.6mm ss with a 25mm hole punched in it
#10
_the gts_
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Posted 31 December 2012 - 03:50 AM
1 x 25mm hole, suprising it still ran, was that a single system or twin and what size is the original pipe?
My internal pipe has been reduced to about 2" each side and the engine had to be retuned quite a bit to get it to run.
The 'bullet' is about 6" long, the end is blank but the sides are thick mesh, its actually 'wedge wire' if anyone knows what that is.
Yes I was considering fitting another set at the flange after the muffler.
What is better at sound deadening, fibreglass or Steel wool? I was thinking maybe fibreglass
My internal pipe has been reduced to about 2" each side and the engine had to be retuned quite a bit to get it to run.
The 'bullet' is about 6" long, the end is blank but the sides are thick mesh, its actually 'wedge wire' if anyone knows what that is.
Yes I was considering fitting another set at the flange after the muffler.
What is better at sound deadening, fibreglass or Steel wool? I was thinking maybe fibreglass
#11
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Posted 31 December 2012 - 08:16 AM
Out of interest, how loud was it before you added the 'bullet' and what is it down to now?
#12
_the gts_
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Posted 01 January 2013 - 04:59 AM
it was in the high 90's which quickly went up to around 120 with a light rev.
That was at approx 3-5m away and at the time but I cant remember the exact set up or the difference between bullets and no bullets and didnt have a tacho connected at the time.
I will be testing again next time I am back in Oz but pretty sure that it is still way too loud.
That was at approx 3-5m away and at the time but I cant remember the exact set up or the difference between bullets and no bullets and didnt have a tacho connected at the time.
I will be testing again next time I am back in Oz but pretty sure that it is still way too loud.
#13
_V6 UC_
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Posted 01 January 2013 - 05:29 AM
3 inch single mandrel system straight thru. Still ran. Fuel Injection lets you get away with it a bit more. Made 98db before plate then 92db and just passed
#14
_the gts_
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Posted 01 January 2013 - 10:09 AM
Out of interest Hayden was that at idle of full noise? from what i have been told the 90 whatever decibles is not at idle.
#15
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Posted 01 January 2013 - 11:57 AM
Mine has a twin 2.5 inch system with straight through mufflers, single each side.
Moderately big cam (232 duration at 50 thou hyd roller)
Tested as per testing proceedure regulations. Engine rpm varies depending on the vehicle/engine being tested. 3600rpm in my case.
Microphone in regulated test position.
Initially 105db.
Plates got me to 97db. Bit of extra fiddling got me to the regulated allowed 96db.
Was clearly quieter at steady test rpm than on backoff, a common pattern according to the testing bloke.
Moderately big cam (232 duration at 50 thou hyd roller)
Tested as per testing proceedure regulations. Engine rpm varies depending on the vehicle/engine being tested. 3600rpm in my case.
Microphone in regulated test position.
Initially 105db.
Plates got me to 97db. Bit of extra fiddling got me to the regulated allowed 96db.
Was clearly quieter at steady test rpm than on backoff, a common pattern according to the testing bloke.
#16
_Viper_
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Posted 01 January 2013 - 12:29 PM
I think it is at half throttle? or possible half of redline? But id say half throttle as you could tell them your redline is 5000 rather then say 6500, but then again if its by throttle your relying on the inspector to judge what is half.
If you had a mechanical secondaries carby would it make it quieter to disable the secondaries?
If you had a mechanical secondaries carby would it make it quieter to disable the secondaries?
#17
_Bomber Watson_
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Posted 01 January 2013 - 03:02 PM
Holding an engine at half throttle no load and no rev limiter will likely cause it to rev untill the valves come out of the rocker covers Clint.
#18
_oldjohnno_
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Posted 01 January 2013 - 03:11 PM
Holding an engine at half throttle no load and no rev limiter will likely cause it to rev untill the valves come out of the rocker covers Clint.
True, but you have to admit that once that happens they become beautifully quiet.
Ah, the tranquility....
#19
_Viper_
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Posted 01 January 2013 - 04:54 PM
Haha i thought they just stabbed the throttle, do they hold it steady?
#20
_Bomber Watson_
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Posted 01 January 2013 - 05:37 PM
From what i have seen they hold it steady at a particular rpm.
TBH i think it varies greatly state to state and who is testing it and how much they dislike you and your car, as with most things.
Cheers.
TBH i think it varies greatly state to state and who is testing it and how much they dislike you and your car, as with most things.
Cheers.
#21
_V6 UC_
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Posted 01 January 2013 - 05:48 PM
I had to do it for him. It was tested at 3000rpm so just held it steady at that
#22
_434LX_
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Posted 02 January 2013 - 08:41 AM
Last time I had a car engineered in Perth, It was a steady rpm for about 5-10 seconds.
#23
Dave6179
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Posted 03 January 2013 - 06:55 AM
Do you want the 3" tailpipes round? Mine (single 3") was a bit noisy, so I made a 'flat' 3" tip... almost like the F#*d GT tips. It measures up at 133mm x 37mm.... 5 1/4" x nearly 1 1/2". The noise inside and outside dropped dramatically. Similar to Harley zorsts, round versus fishtail.
And, it matches my tail lights and the recess in the bumper! Just a fluke that bit.
And, it matches my tail lights and the recess in the bumper! Just a fluke that bit.
Edited by Dave6179, 03 January 2013 - 06:56 AM.
#24
rexy
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Posted 13 January 2013 - 02:37 PM
Found a used one in the shed. This was in one side of a 2.5 inch twin system.
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#25
_cruiza_
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Posted 13 January 2013 - 02:46 PM
another trick I have seen on the race track is change the tips on your exhaust to ones that droop down pointing the exhaust down onto the ground when measured at X meters away much quieter as sound is directed down into ground
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