Half an hour from here we have Circuit Zolder and they have some free driving days but the dB limit is 95 if I remeber correctly.
Was wondering what I could do to reduce the noise. I am working on an airbox already but what do you think about reducing the dB coming from the exhaust ?
( which I like for driving in the road )
Have heard of some kind of dB "killer" which you can just put on your "tailpipe" ?
( do not remeber the correct name anymore .. ) ?
Would help me when I want to go out there some day.

I fitted a DB killer to my exhaust at SVA time. It did work to bring the noise down a bit (104 db to 100.99 db) but it is very restrictive compared to a straight through exhaust.

Link to Ebay

If it's just for one day, you could try it. But to be honest people have had better results using larger silencers.

HTH

Mike

Db killers are a waste of time IMHO, they strangle performance and the engine runs hot,not really what you want on a trackday. As Mike said, the most effective silencer is a BIG one, are you bec or cec? If its a bec 95db
is going to be fairly hard to achieve. As you have already realised induction roar is a big factor, and if the test is driveby, pointing the exhaust outlet under the car and down towards the track surface helps. I never go to Donnington now as i struggle to get down to 98Db.
Al.



]Originally posted by Jos Fury
Half an hour from here we have Circuit Zolder and they have some free driving days but the dB limit is 95 if I remeber correctly.
Was wondering what I could do to reduce the noise. I am working on an airbox already but what do you think about reducing the dB coming from the exhaust ?
( which I like for driving in the road )
Have heard of some kind of dB "killer" which you can just put on your "tailpipe" ?
( do not remeber the correct name anymore .. ) ?
Would help me when I want to go out there some day.

For the exhaust noise use a silencer that is as big and long as you can get. I don’t know if you use a “cat” but that will certain eliminate a great piece of the noise. Let the and of the exhaust faced to the ground and when possible at the back of the car.

Perhaps you could consider fitting some Foam in the engine bay, such as the stuff that NoiseKiller sells.

http://www.noisekiller.co.uk/materials.php

Or the Dutch seller: http://www.noise-killer.nl/Engels/Products.html#Foil_Faced. Foil Faced is the stuff that I used in my car, and it works.

At the air intake you can rid of most of the noise. Don’t use an open type of Filter (K&N, etc). An airbox will be the best way to get the engine silent. Use a paper (original) type of filter. And make al long piece of hose in front of the airbox that sucks the air into the airbox. This will act like a “Helmholz resonator” and flat out the air induction noise.

These things will certain reduce the noise to a legal level. With my car I had to reduce the noise level to a maximum of 80 db(A) (dynamic road test) to get it registered by the RDW here in the Netherlands.

Gr. Roy.

[Edited on 12/10/07 by dr-fastlane]

Yup. You need a hugely big exhaust can... My bro has done some fancy smancy equations for his RGB racer. It's going to be BIG... For SVA there are a few "adjustments".

My tacho was infinitely adjustable and it appears it was over-reading by about 25% at the SVA test

Oh well. Whisper quiet (it helps mines a V4 with pipes down both sides so they only measure 50% of the noise during the test)

Fit as big a silencer as you can, or fit two.


park straight


edit: sorry for the big pic

[Edited on 13-10-2007 by smart51]

thanks for the info. enough to think about and figure someting out !