Custom exhaust to meet track dB limit

[cantfindausername]

I had my car noise tested last night at Brands Hatch and it came out at 109.8 dB. This is well above the noise limit for any kind of track day or testing session.

So I'm looking into what options there are to reduce the noise. Custom exhaust, dB insert, etc.

I don't really know that much about exhaust fabrication, but would like to have a custom one made, but with the guarantee that it will meet the noise limits while still being free flowing enough. Or am I after the impossible there as free flow = noise?

Any advice, or links/contact details would be great.

Thanks,
Ant

[Julian]

You have a particularly tricky problem with the mid-engined layout as it doesn't give much room for silencing but typically turbo cars don't have too much trouble as the turbo itself does a very good job of reducing the exhaust volume. Given this last point it is quite possible that the exhaust you have is acting as an amplifier - again not an unusual thing to happen with turbo cars where the exhaust uses a large bore to get the gas out with minimum fuss.

I've had a variety of silencers on my car, with and without turbos and never managed to get it that loud which suggests to me that you need to get a variety of noise readings across the rev range and see where it peaks. I think you'll find that you have a resonant frequency that matches fairly closely with the revs you are asked to hold when testing normally.

As to how to fix it - not so easy but your exhaust builder should have some ideas, if he doesn't then you may want to find a new company. The problem is that a lot of companies build the exhaust on the car to guarantee correct fitting with little or no regard to noise levels. Last time round I used a company called JWE exhausts in Macclesfield (a bit out of your way) but they were far more proficient than the other companies I've used in the past and had a great number of designs on record going back something like 40 years.

[cantfindausername]

Thanks Julian. I've been in touch with a few companies, and I'm making sure that they're aware of my requirement for noise restrictions.

My stance on it will be that its sold as an exhaust to meet such requirements, and should it fail this then it is not fit for purpose.

I've been quoted £290 for a twin silencer single exit system by a company in Cardiff, and am awaiting about 2 or 3 other quotes back from other companies. I'm being a bit particular with who I approach. Inparticularly one's who have expereince with track and race cars as I guess these have a greater knowledge of what is needed to quieten a car to a respectable level.

Ant