easy (removable) exhaust noise suppression

[s2driveruk]

Need some quick pointers on the art of hitting a noise test figure.

Car was tested before a session at VAG day at Castle Coombe yesterday and 4500rpm, 45 degree angle and .5m away, was 103db - limit was 98db

With a letterbox tailpipe, i couldn't bolt up a secondary silencer so any other ideas???

to confirm the current setup, no cats, single smallish back box and single pipe to letterbox tail.

Need to get it sorted ahead of ADI....I need to get it on track

Cheers
David

[Error404]

i think you really need a removable 2nd box matey.

dB is a logarithmic scale so 103dB is is half as loud again as 98dB so you need to do quite a bit to quieten that beast down

[s2driveruk]

is it really that much louder than 98db?

[Jamo]

Yes it's actual a factor so 98db is 10 to the power of 9.8

103 is 10 to power of 10.3

In figures 98 db = 6309573445 and 103 db = 19952623150 !

[s2driveruk]

any ideas what the effect of refitting just one of the cats would be....would it drag the noise back down enough and still be reasonably free flowing?

[Rusty]

Cats do make a difference, as above, get a centre box back in there, better than having the cat in the system at an important point earlier on! Not had mine tested yet but cat and decent back box should be OK...

[quattro]

any ideas what the effect of refitting just one of the cats would be....would it drag the noise back down enough and still be reasonably free flowing?

Are you talking OEM cat? that would be very restrictive, i would just go a head and get a nother box fitted.

[s2driveruk]

i'm looking to keep the sound as is except for when tracking it to meet a noise limit. refitting one of the oem cats is a pain but is cheap (i.e. no cost) and should bring it down to around the limit I would hope. Trying not to spend money making the car quieter I might just get the letterbox shaped tail removed to a standard round tail so i can just bolt up an extra silencer. It a pain that Castle Combe is limited as much as it is. the car sounds great as it is, seems a shape to shut it up to get it out on track

[turbodriver63]

would someting like this be of any use?
http://www.demon-tweeks.co.uk/Perfor...sert/2050/5120

[s2driveruk]

yeah thats the kind of thing, however it needs a long straight section which on the coupe is a problem with the box running across the back of the car

[Fat Audi 80]

David, are you running twin bypass pipes? In which case you may need to bolt up BOTH Cats again to pass the noise regs. I see this the cheapest (no cost) way of doing it in the short term....

The cats will only rob 20 bhp or so won't they?

(Or fit the cats for the noise test then whip them off again in the pits! )

[Rusty]

Cats aren't too bad on a stock car (mine was running stock cats when I got the RR runs of 294 and 297). It's more that a properly designed silencer is less restrictive than the emission friendly Audi cats.

David, I'd spend a little £ on a centre box that gets it to the correct noise and leave it, exhausts are a PITA to keep messing with. If you're really keen for noise then get a cutout valve under the rear seats

[s2driveruk]

thinking cats on for the session then just to get on with driving it then maybe a longer term solution for the future.

In terms of noise, at the moment i think its spot on, the sound is liberated from the car with no cats and its sounding more like i wanted it from day one BUT i cant be bothered with ongoing hassle to swap bits out whenever i want to venture out on track. It went round the ring and didnt trigger anything and the limit there was 98db which again it was well above.

Cheers for the input guys

[Rusty]

98dB drive-by is rather different to static test.

Suggest that you look into a full system including 3" DP and do it all properly. Prospeed were good VFM and did a nice job, will soon know if my setup passes, could do a lot worse than replicate that IMHO

[HPmuirt]

I like the idea of converting to a single cat system and then running a high flow cat on one side have a diverter valve into a short length of pipe which exits to atmosphere before it reaches the rear of the car.

You could either manually open the valve for track use using something like this or have it automatically open on full boost with something like this.

Cheers n

Si