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Author: Subject: Exhaust too loud

posted on 21/1/20 at 06:55 PM Reply With Quote
Exhaust too loud

Hi Guys,

Planning on doing another track day or two again this year but have been thinking about my exhaust.
I blew 99db on my last track day at Bedford static (limit is 101) and got talked to twice about the drive by noise....

I thought i'd check the exhaust hoping that there's no packing inside or something but looks ok to me, although i don't really know what it should look like. It's packed pretty full, isn't solid or anything and has plenty of 'sponge' still, also pulled a little bit out to look at, does this look ok to the educated?

Otherwise what are my options to make the car a bit quieter for track without killing loads of power?


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posted on 21/1/20 at 07:27 PM Reply With Quote
There are a few options mate. Ive been chucked off Bedford for noise.....after 1 lap! money well spent lol

Have you tried using the Acoustifil/ Acoustafil packing. Its almost like a duvet that you wrap around the perforated tube and probably the cheapest option.

A bigger end can but this can cost a few quid

A Db killer that fits into the end of the exhaust

Hope you get it sorted mate and hopefully see you on track at some point

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posted on 21/1/20 at 07:29 PM Reply With Quote
The stuff inside is the fibre glass type material, i got the exhaust with the car so haven't changed anything on it, have looked at acoustafill which i'm happy to do if it's likely to make any difference......
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Mr Whippy

posted on 22/1/20 at 07:02 AM Reply With Quote
I used a straight through carbon motor bike can on my vw beach buggy only to find it disappointingly quiet, it did an amazing job of silencing the noise and ran cool enough that I could hold the outside of the can with my hand. That was on a 1600 engine with a 2 inch bore.
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posted on 22/1/20 at 07:17 AM Reply With Quote
What size is the silencer?

I would think you should have at least 6" to stand a chance of passing lower limit tests. I've got 6" on my Duratec powered car and that is still quite loud. I did fail drive by at Brands but I think that was induction noise, I now have an airbox I can fit over the air filter if its ever a problem again.

[Edited on 22/1/20 by peter030371]

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posted on 22/1/20 at 02:18 PM Reply With Quote
putting a turbo on will kill the noise
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posted on 22/1/20 at 10:40 PM Reply With Quote
After getting kicked off at Brands I have fitted an airbox and had a secondary inline silencer made up, look in my photo archive for pics.

I didnt notice a big difference with Acousta-fil. I also fitted a DB killer after getting pulled at brands and still got kicked off, it also seemed to make no difference.

I have not used my car for years so have no idea if my changes have worked!!

Track days ARE the best thing since sliced bread, until I get a supercharger that is!

Please read my ring story:

Me doing a sub 56sec lap around Brands Indy. I need a geo set up!

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posted on 23/1/20 at 05:44 AM Reply With Quote
Exhaust design is a bit of a black art.
Length of pipes can make a bg difference, but here you don't have room to experiment.
The principle that bigger is quieter applies, so a larger diameter box will help.

Regarding power, loosing a few BHP is a small price to pay for being able to take part, so having an emergency plan is worthwhile. I carry a 1" wide strip of steel, about 6" long that is bent to it can cover the outlet, and be clamped in place with a jubilee clip.
I also wonder if an adaptor could be used to turn the outlet though 90degrees to point the exhaust straight down to the road, sending the noise in all directions?
A better plan may be either a BIG silencer, or even fit a std can off a bike that will be nice and quiet. Yes, a few bhp gone but an easy/cheap fix. And if you compared lap times I bet it wouldn't make a seconds difference.

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posted on 24/1/20 at 01:51 PM Reply With Quote
Thanks all, didn't get a chance to actually measure up the box, definintely would have room to add a bit more length, probably at least another 6 inches or so although don't want it looking stupid on the car!

Diameter wise i don't think i'm going to be able to add much more as already pretty close to the side of the car....

Maybe i'll look into a longer can or a bike can and see if that makes a difference...

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posted on 24/1/20 at 07:21 PM Reply With Quote
Increasing the width has had a greater effect on noise (for me) than increasing length.
Castle Combe limits, e.g., are harsh, very.

A short tailpipe add-on (e.g. the Merlin thing, funnily enough they're at Combe) may help (it did me with a C20XE just on the limit) as a temporary solution for NIMBY circuits.

6" diameter minimum, stainless steel, loosely freshly packed. Airbox, etc. Back off when going past the drive-by sensors.

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