E30 Zone

Having trouble with static tests on track days, I am reading over 108db at 4.5k. Do not have any problem with drive by limits mind.

I have tried inserting a decibel reducer but it did not have a noticeable result.

It is a 320, pics of the exhaust:


The cat and middle silencer appear to have been removed.

What is the best solution to my problem? New exhaust or messing with the existing one?

I have no interest in having a chavvy exhaust so just want something reasonably quiet without being restrictive. Sub 98db so I can show up to tracks confident I will actually get on track!

Advice appreciated!

I would try putting a centre box in first

Yes I thought that would be the way to go thanks. Is this an off the shelf thing or do I need to take it to an exhaust maker or something? I really do not know much about it sorry!

It looks like someone has bodged that beauty together themselves.

How are you with a welder? I would weld in one of these:

http://exhaustpartsuk.com/index.php?mai ... x&cPath=34

followed by something like this:

http://exhaustpartsuk.com/index.php?mai ... _1323_1328

With appropriate supports.

Alternatively any exhaust specialist will sort it for you, some better than others

I have a similar problem with my 325i. It has an Ashley system and when we got it (new) 3 years ago, it never caused a problem. Like you, drive-by isn't a problem (you can hardly hear it!) but at static tests, it seems to resonate a lot. This may be to do with a rigid mount (ooh, er, missus!) to the boot floor. However, it does seem to have deteriorated with age - I'm guessing 8K miles. One option is to fit a middle box if I can find one small enough to avoid grounding on rough roads and speed-bumps. Short term, I may just re-pack the back box.

Anybody re-packed their box? Which material did you use?

I went to an exhaust place today and they are going to fit me a centre box next week. They are going to have to rotate the existing downpipe a bit to get the clearance. I am a little concerned about the clearance as when I was under the car you could see it had already been scraped where the new box will be put, worried I might rip it off?

Anyway they quoted 120+vat which seemed like a good price so I will get it done and go and get a noise test done so I can report exactly on the difference it made.

There are a few things wrong with that exhaust:

1. The rear box is FAR too small - general rule of thumb is that you need about 10 - 15 litres silencer volume for every 1 litre engine capacity as a minimum so you need about 20 - 30 litres silencer volume.

2. The silencer is the wrong shape - being nearly round it will only take out noise across a small frequency range - a large oval rear silencer box helps to take out low and high frequency noise. 2 boxes are always better than 1 - first one takes the edge off whilst the second does the bulk of the noise reduction.

I bet that rear box has little or no silencer material in it - best type of silencer for trackdays are absorption silencers (perforated pipes straight through with material packed in the silencer box trouble is, if these are done badly, the material just burns away and eventually you end up with an empty box...).

If you fancy going ahead with your solution above, then good luck, hope it works out! But you may well have to replace the rear box as well - might be worth pricing up a whole system?? Could be cheaper in the long run...

Generally, only two types of filler are used, E-glass and Basalt. Basalt is used for racing applications as E-glass doesnt stand up well to high heat, but Basalt blows out easier.

When repacking, make sure not too pack it too densely or the sound waves will not have the ability to penetrate deep in to the silencer. Width is usually best rather than length.

As the actress said to the bishop...........!! Boom boom!

Sorry - couldn't resist...

Hi, Demlotcrew, would you advise that the larger silencer is placed after the smaller silencer?

Thank you

Andrew might beat me too this, but yes...! Space also dictates this on the E30...

It depends on the packaging requirements of the car, if you can have a large centre section and a similar sized back box that would work well, keeps the weight in the centre of the car and like Mike said, the second box will do the majority of the sound absorption.

Single pipe exhausts are always louder anyway.

I had assumed that the rear silencer was knackered but the exhaust man knocked on it and said it sounded fine to him. I will ask about a bigger back box though anyway when I drop it off next week.

Thanks for the advice!

For those who enjoy closure: I had another noise test done today after having the middle silencer installed and it read 94db this time. Problem solved.