Back box delete over 100dB's - Too much for Track day

Z

Zikim

Active member
I have fitted a back box delete but I have just had it tested at half a metre and it reads 103dB's which is higher than the allowed by most track days.
Is there anything that I can do to reduce the noise level so that it gets below the 100dB level?
I still have the standard 3.0i backbox - what would be the best mod to do on this to make it louder than standard but still pass under the 100dB mark. Incidentally the standard box makes 86dB's at 4,500 revs (at half a metre).
 
Backbox delete comes with some pretty hefty low end performance loss so probably not the best for a track anyway :thumbsup:
 
Disca said:
Backbox delete comes with some pretty hefty low end performance loss so probably not the best for a track anyway :thumbsup:
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I'm glad you didn't say that it robbed top end power by 20bhp otherwise you would have re-opened that past lively debate :fuelfire:

Seriously, is there any way to make the bypass quieter?

Or what is the best way to modify the standard box for optimum noise but still be below 100dB's?
 
Scooba_Steve said:
Put the backbox back on and have a small bypass? You could tailor that with diameter I would guess.
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Is that to take an external pipe from the inlet side of the exhaust to the outlet side?

If it is, it seems the same as the exhaust mod that was done on the S2000 that I did, sounded nice on the S2000 but only a small improvement. On the Z4 how big an improvement would this mod be?
 
Yes, I don't see any other way short of having something custom made but have no done it so no idea as to effectiveness. You're obviously going to have to compromise as it's clearly too loud to track - could a custom system be tuned for an exact dB level?
 
you can buy things that bolt to an existing exhaust that help on trackdays. its a common ish issue in the kit car world to have a noisy exhaust. a few of the tricks that you need to remember are daft but do make a bit of a difference. one is to make sure your static test is done well away from a wall, also alot of the westy exhausts have a bent tail pipe that if you point more to the ground/ slightly under the car makes a difference. (strangely)

failing that ive seen a few people cheat by shoving wire wool up the exhaust for the test and then just lifting off as they go past the drive by. not that i would recommend this tho as it sounds a ropey as hell and a dead give away when it blows out during the test.

i would have expected 100db to get though.
 
Scooba_Steve said:
Put the backbox back on and have a small bypass? You could tailor that with diameter I would guess.
Click to expand...
Has anyone got any pictures of the backbox bypass mod that they can show? Is it sweeping bends and what diameter of pipe is used for best effect?
 
A few have defo done it on here - I don't think they've done smooth pipework and I think in your case you need to tailor the diameter for the sound level rather than best effect.
 
Scooba_Steve said:
A few have defo done it on here - I don't think they've done smooth pipework and I think in your case you need to tailor the diameter for the sound level rather than best effect.
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Sorry, I was meaning the best noise when I said best effect
 
The simple fact is track day noise limits are getting lower and stricter and that isn't going to change. Your best option balancing performance and noise (I mean volume not quality) is the OEM system.

If you want to do track days I would re-instate the original backboxes. It's what I did.
 
Would removing the centre silencer give a bit more noise but still be under the threshold for track days?
 
Possibly Neil.

An alternate would be a custom backbox, would allow you to control the noise levels.
 
As mentioned earlier in the post why not just fit trackday silencers
Call a company like this for suggested solutions:

http://www.actproducts.co.uk/silencing/trackdays/

Loads of links on Google to others
 
cj10jeeper said:
As mentioned earlier in the post why not just fit trackday silencers
Call a company like this for suggested solutions:

http://www.actproducts.co.uk/silencing/trackdays/

Loads of links on Google to others
Click to expand...

they just look like standard re packable cans. get them filled with acusti-mat and they will pass. most 7 typre cars only have one of these on their system period and can pass so im sure a Z will be no problem. you do have to keep replacing the packing every-so often.
 
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