Need to drop a couple of db after my iva fail and thinking of a few ways to do it (101db should be 99 and less). Some kind of DB baffle would be the obvious choice. Can't put it in the tailpipe as it has a 45 degree exit as most of ours do. My exhaust from turbo back is one piece tig welded and not by me so altering that means calling friends for favours (and rightly waiting til they're not busy). That being said the last bit after the silencer is tacked only with this in mind.
I had an idea of making a copper 'gasket' on the turbo downpipe flange that restricts the flow from 3" to much smaller. Do you think it would deaden the sound much and still flow well enough at fast idle for the emissions test.

Any other ideas would be appreciated. I've heard of use of wire wool in the silencer but I have no idea how that's done and doesn't sound very effective to me anyway.

You should check the rpm for maximum power, noise check is at 75% of that.

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Originally posted by gremlin1234
You should check the rpm for maximum power, noise check is at 75% of that.

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Get the dyno operator to slowly come off the throttle after your desired max power RPM, no need for a bad map

or a rev limit /limiter

I put baffles in the exhaust joint, simple piece of ally with a load of wholes in it.

Did have to trailer the car though.

When I was starting the rev the car, the examiner told me to stop and said that was ok this time, but still have 1000 rpm to go

Any restriction will work far better at the tailpipe end than anywhere else. Reducing exhaust noise is all about slowing gases down by the time they have reached the end of exhaust & having space within the system to allow gases to expand before effectively hearing the original explosion by the time it reaches the tailpipe. I have cut & bent our standard Db killers before to fit within 90 degree tailpipe, adding wadding further up inside the exhaust held in place by the Db killer used as a baffle at the end of the exhaust will definitely work - to what extent will vary from system to system, but it's fairly easy to reduce noise without strangling the system.

We have Db killers & wadding on the website, if you want to ring for advice no. is on there

If the car has already been tested & failed going back with a different map saying max power is 2000 revs lower than you've stated on the form is hardly likely to impress them - they aren't stupid!

I had the same problem at my IVA test. The tester did mention that other people have tried the wire wool trick. He said that it did work but that he had seen a couple of examples of where it was not put in securely enough and a glowing ball of it had shot out during the test (he called it a burning rat!).

I solved mine with a DB killer. Like you, I couldn't put it in the end because of the bend in the pipe, so I just took the end off, placed it direct in the end of the silencer and then put the end back on again.

I had a major problem with this. As said above, the nearer to the tailpipe you put the restriction, the better.
I tried all manor of things to find this out! Ended up with some simple homemeade baffles, which take 2 or 3 db off

Pointing the exhaust exits towards the ground a bit can help as well, if you can rotate them at all.
And to be sure, to be sure, I may have wedged some wire wool up there just outside the test centre, the baffle ensures it can't come out. That took about 5 db off so is definately the most effective way.

The wadding is a lot better than wire wool as, one, it won't burn!, Two, it expands with heat & it stays in one piece so as long as you have a baffle of some sort between it & the end of the pipe it won't escape as wire wool is inclined to!

Just found this while clearing the garage ..
Passed IVA with a very quiet exhaust ...







Knock the lip of tip insert.. knock lip back on ..

Side Exhaust
Bit of Stainless wool round it..

[Edited on 9/2/15 by johnemms]