987 exhaust noise reduction

[tcreswick]

Hi All,

I realise this might be an unusual question, but I track my 2007 987.1 a lot and have been having issues with both static and drive-by noise limits. The car now static tests at around 105-107 dBA, and at Brands Hatch I'm hitting ~ 97dBA on the drive-by, although I don't know the exact position of the mics and it seems highly dependent on how late I brake (and downshift) going into Paddock.

It's got a Carnewal GT exhaust (fitted 3 years ago). After that it was testing around 95 dBA static, so it's got louder since then. Gert assures me that these exhausts don't have any packing, and nothing inside that can fail and make them louder. It's been suggested that the primary cats might have started to fail, but I would have expected CELs or emissions test issues if that were the case. They're 12 years old now, so I guess that's a real possibility, but curious if anyone has experience of that.

I'm slightly concerned that some of the noise and resonance might be related to other modifications - it's got an Aasco lightweight flywheel and semi-solid engine mounts. The induction system is stock except for a cotton filter.

I can't think of a clever way of breaking down where the noise is coming from, but it means that I'm a bit stuck on how to solve it at the moment. I don't want to throw a whole new exhaust system at the car only to have the same issues.

I've been looking at the FVD full system which they call "quiet" (https://www.fvd.net/de-en/BES987C0201S/exhaust-system-987-cayman-brombacher-quiet-200-cell-cats-tips-2x90mm.html), and have emailed asking whether they have noise measurements for it. Does anyone have experience of that?

Thanks,

Tim

 

[Motorhead]

Tim,

It might suprise you that there are experimental techniques available to identify sound sources for what is effectively pass-by noise, but they're well beyond the scope of an individual. Apart from the intake and exhaust, tyre and mechanically-induced sound add to the complex mix.

As you point out, exhaust system components degrade with age and unfortunately it's more likley that the effect will be negative rather than positive. The cats are part of an active system with a programmed tolerance band which may well adapt with mileage, hence no CELs?

I'm not sure about the effect of your lightweight (single mass?) flywheel but it's more likely that your modified engine mounts will reduce engine isolation and lead to more sound being radiated from the body, although I would think that would be marginal compared with the other primary sources.

All of which I'm afraid doesn't really help you because the only way to get an improvement is to change components by guesswork - an expensive remedy..! I suppose you could try fitting an exhaust deflector to point the flow downwards or at least away from the track mics.

I believe that the Brombacher kit is good but seems like a very expensive solution. I believe that Brian Innes (BJ Innes) looked at them for his 718CS. Maybe you should just consider replacing the cats as a first step?

Jeff

 

[gmcraib]

I also have the carnewal exhaust. It is very loud!

With the other stuff I have now it’s even louder!!

Best advice would be to short shift or let off near the microphone if you can find them. Someone is bound to know.

Alternative is to make a noise reducing baffle. I had a patent for this a few years ago and made a prototype up. But there was already something similar on the market so had to pull the patent.

I might be able to help you though. PM me.