Your Exhaust Decibels

I wonder how loud my mates mk1 20vt will be

TD04 Turbo, 3" downpipe, and 3" side exit with one small box in the middle :/

 

1.8 16v, twin 40's, 4 into 1 manifold, gas flowed head, scorpion two box system = 101db at 1m and 45 degree angle.

 

all depends on the design of the small box, I visit a exhaust manufactuer quite a bit and there is a alot goes inot desgning a box for a road car, and a small change in the amount of wadding, or size of perf can ake a few db difrerance, as can tail pipe design (down turned is generally quieter than straight out)

also turbos kill some noise, both my etsate and the wifes tdi polo run no silencers, just the cats mines a bit annoying at times, but the wifes with the smaller turbo and pipe bore gives a real nice deep note with out being ott

 

The old Renault 5 Gt Turbo race cars run with no silencers at all, and a side exit! I think they are around 97db - so quite quiet really.

 

At Bedford for the javelin/cgti day my mk2, abf, flowed head, ported cast manifold, 2.25" supersprint single box static`d @ 97.5db @ 4500rpm. Within 6 laps I`d had the noise board waved in my direction meaning I`d reached 86.5db @ 20m driveby.

And ref to single/twin box systems, the ported manifold and the single box system, definitely made a noticeable difference, much more eager to rev, pulling harder and felt a lot more lively compared to stock mani and three box magnex.

Would be interesting to see if a slip on downturned tailpipe would make enough difference at bedford to avoid nudging the sound limits with my set up.

 

Thanks for the info/advice chaps. Interesting to hear your experience at Bedford Bryn, as we have relatively similar setups on our cars. Think I'll go down the 2.25" 2-box route to be safe, but get the pre-beam box drastically reduced in size compared to the Jetex system on there at present. Will post up when I get a noise reading!!

 

my old mk1 was on a twin box 2.25" jetex system, 1.8 8v with a280 deg cam and heat wrapped 4 branch mani, that was less that the 98 db at donny even on full chat.

becareful when having a box reduced.. as it could lead to booming at certian revs when crusing, or give flow issues if you are not careful.

GT2 - a slip on down turn will help for sure

 

If you're racing, and every last bhp and every kilo is sacred, then it's probably worth the aggro of sailing close to the noise limit, and carrying a 'spare' exhaust section if you fail noise test.

However, if you're running a track day car, then you should go twin box for an easy life, or risk being sat in the paddock all day wasting your money.

 

I did know it would be close, so had the previous 3 box magnex along too, so only lost about an hour changing the complete system. Not ideal, but better than going home early!

Will have to see about picking up a slip on downturned tailpipe.....

 

Hi all,

Did Bedford yesterday - first time for the Mk1 - self measured the exhaust noise at home a couple of weeks ago with a decent sound tester and got 85 Db static at 4000rpm at 45 degrees and 500mm away

Bedford is 87.5 so I was worried and brought along an additional tailpipe silencer - but went out and eased off at the 3 mikes at first and ramped it up gradually but got greens all the way apart from an amber when I passed the first mike after the start straight hairpin very close behind an Exige with both of us on full chat

If your car is near the limit stay away from other noisy cars or ease off when passing the drive-by mikes - especially noisy ones. Dont forget that induction noise is louder than you think - my car also registered 85Db at the front with the bonnet shut so if your exhaust is near the limit or on it the induction (especially open bobble throtties) can tip the balance on N/A cars.

Roughly speaking a 3Db increase is a doubling of noise level.

I`ve got a supersprint 4-2-1 into a 60mm custom stainless system with a 100mm intermediate silencer and an offset oval back box with upturn which reduces noise much more than a straight through box without sacrificing flow too much