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Jan 25, 2016 21:14:21 GMT
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Hi folks
I've got a bit of a problem. I'm booked in for a track day at Goodwood at the end of Feb. There is a noise limit of 98db measured 50cm from and 45 degrees to the exhaust. So I bought a cheapie Maplin sound level meter just to check. The car is a bit loud on the road but not excessive, or so I thought! Well I checked it tonight and got over 100db!
The car is a mk1 cortinaman gt with a precrossflow on a single DCOE and GT manifold and stainless exhaust with two boxes. Any ideas what I can do to make it quieter, ideally quick and cheap!
Cheers
Cortinaman
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Last Edit: Jan 25, 2016 21:15:15 GMT by cortinaman
Old Fords never die they just go sideways
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Jan 25, 2016 21:23:57 GMT
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How big is your tailpipe? if there's room to put a bung in that'll reduce the volume a bit. They're on ebay as "DB killers".
Basically they're a slight restriction which'll increase the pressure inside the exhaust making the baffles do a bit more baffling.
How long is the tailpipe out of your backbox? if it's really short, extending it can make a difference. I had a custom exhaust made for my T25 - it's rear engined so I had two of the biggest silencers I could fit across the back valence, but it was still an animal - Popping and banging like mad and mega raspy. Awful on a van.
It was 2.25 bore, but there was only about 10cm of tailpipe. I added a bolt on 15cm extension and it made such a difference.
Orions were always quieter than Escorts!
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Last Edit: Jan 25, 2016 21:27:05 GMT by cobblers
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longman
Club Retro Rides Member
Posts: 506
Club RR Member Number: 3
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Jan 25, 2016 21:31:05 GMT
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What he says ^^ plus a load of wire wool up the pipe ,if you fail that test they can do another which is half way down the car .
The noise meter is just after the chicane so go easy there if you remove the baffles after the test.
They are pretty good at Goodwood for noise and if you are near or at the limit they tell you where to go easy .., or at least they did with me.
Have a goodun
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Paul
98 500 SL
86 911 Carrera/sold
23 Octavia Phev
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Jan 25, 2016 21:42:35 GMT
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How big is your tailpipe? if there's room to put a bung in that'll reduce the volume a bit. They're on ebay as "DB killers". Basically they're a slight restriction which'll increase the pressure inside the exhaust making the baffles do a bit more baffling. How long is the tailpipe out of your backbox? if it's really short, extending it can make a difference. I had a custom exhaust made for my T25 - it's rear engined so I had two of the biggest silencers I could fit across the back valence, but it was still an animal - Popping and banging like mad and mega raspy. Awful on a van. It was 2.25 bore, but there was only about 10cm of tailpipe. I added a bolt on 15cm extension and it made such a difference. Orions were always quieter than Escorts! The tail pipe is about 40cm long coming out of the back box, so not too short, and the diameter is pretty small. I'll see if I can find or make a db killer. Cheers for the advice. |
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Old Fords never die they just go sideways
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Jan 25, 2016 21:44:09 GMT
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What he says ^^ plus a load of wire wool up the pipe ,if you fail that test they can do another which is half way down the car . The noise meter is just after the chicane so go easy there if you remove the baffles after the test. They are pretty good at Goodwood for noise and if you are near or at the limit they tell you where to go easy .., or at least they did with me. Have a goodun I'll try the wire wool! Thanks for the tips on the mic locations. |
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Old Fords never die they just go sideways
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Jan 25, 2016 22:20:10 GMT
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If you can't choke it down, a random bend on the end will help too - A change in direction is as good as a change in diameter and will dissipate energy (noise!) and aim it away from the microphone.
There's a picture floating about the net of an Evo with a 90 degree bend on the tailpipe that's melted the number plate off.
The bend was done to aim the noise away from a microphone on the main straight of a particular track.
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Jan 25, 2016 22:51:37 GMT
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well I checked it tonight and got over 100db! 100db is loud! Think 2 stroke MX bike on full chat, are you sure its working correctly? You can get free db meter apps fpr smart phones etc |
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sb
Part of things
Posts: 725 
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If you can't choke it down, a random bend on the end will help too - A change in direction is as good as a change in diameter and will dissipate energy (noise!) and aim it away from the microphone. There's a picture floating about the net of an Evo with a 90 degree bend on the tailpipe that's melted the number plate off. The bend was done to aim the noise away from a microphone on the main straight of a particular track. Laguna pipes, after Laguna Seca:   Apparently the Evo caught fire a little rather than just awful aim. |
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Wire wool blows out over a short amount of time, but is good for a one off noise check. Just don't use the brilo pads with soap in them, otherwise whoever is following you will get a right whiff when it burns off!
Another one that works (or at least has on rally cars i service for) is bend up 2 pieces of metal wire/rod about 2-3mm thick. Make them into an X with bent/barb ends so it can be pushed into the exhaust and holds in place. With the X right in the flow of the gases just at the end of the tailpipe.
This disturbs the air flow (without restricting it) and reduces the db's
Wasn't sure first time i saw it but we tested it several times and there is a noticeable small reduction in levels.
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Jan 26, 2016 15:54:48 GMT
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A simple chrome trim that points exhaust down to the ground will reduce by approx 1db and possible more.
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93fxdl
Posted a lot
Enter your message here...
Posts: 2,000
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Jan 26, 2016 17:00:18 GMT
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As an aside, I was told that db scale is not linear, but every 3 db is double the noise, trouble being since you are 3 db over, it looks like you need to halve the noise, but remember to measure in an open space, so as not to be adding reflected sound to your total.
Ttfn Glenn
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3db isn't twice as loud, its twice the SPL sound pressure
From memory 10bd is twice the volume
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It increases logarithmically if I remember correctly.
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Thanks for all the advice folks.
Dodgerover - I did wonder if the cheapy meter I bought was giving a duff reading. Goodwood will test sound levels FOC before the day, but it is a bit of a trek. I'm going to try out some of the suggestions and see what I can get down to.
cheers
Cortinaman
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Old Fords never die they just go sideways
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Jan 27, 2016 13:00:57 GMT
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i'd take a third considerately designed silencer over any other bodge or restriction tbh (or make sure you current ones are big enough and still have packing)
never had an issue with my track day car, and thats on 2.5 inch pipe work and open throttles
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Last Edit: Jan 27, 2016 13:01:55 GMT by darrenh
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MrSpeedy
East Midlands
www.vintagediesels.co.uk
Posts: 4,786
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Jan 27, 2016 17:53:07 GMT
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An old racing GoKart trick is to put a large (3/16" or bigger) split pin across the tail pipe. This would knock off 1-2dB and scrape through a boarderline 250cc 2 stroke  |
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longman
Club Retro Rides Member
Posts: 506
Club RR Member Number: 3
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Jan 27, 2016 18:21:25 GMT
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Thanks for all the advice folks. Dodgerover - I did wonder if the cheapy meter I bought was giving a duff reading. Goodwood will test sound levels FOC before the day, but it is a bit of a trek. I'm going to try out some of the suggestions and see what I can get down to. cheers Cortinaman are you near any other race track? if you are, pop over on a trackday and they will test you for free , got mine checked at Brands before a 101 db day , I was @ 103..... |
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Paul
98 500 SL
86 911 Carrera/sold
23 Octavia Phev
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i'd take a third considerately designed silencer over any other bodge or restriction tbh (or make sure you current ones are big enough and still have packing) never had an issue with my track day car, and thats on 2.5 inch pipe work and open throttles I was thinking along the same lines - an extra silencer hung off the rear bumper mounts. I suspect the existing silencers are not doing much, but I kind of like the sound of the exhaust as it is now! cheers for the advice. longman - unfortunately Goodwood is my nearest circuit - and is a two hour round trip, so not too far, but far enough! |
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Old Fords never die they just go sideways
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Iain
Part of things
Posts: 351
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I've heard a vertical metal bar/pole through the end of the tailpipe helps (like a 10mm wide strip or something tacked on the inside)
I have an decibel reducer insert that I take to trackdays if needed, it doesn't even fit in the pipe properly (2" insert in a 2.25" tailpipe) but it does reduce the noise.
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mk2cossie
Club Retro Rides Member
Posts: 2,980
Club RR Member Number: 77
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Jan 28, 2016 13:34:14 GMT
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Also don't forget that the noise test is 3/4 max rpm and held, and also in an open area. Or at least at Brands Hatch it is  |
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