reduce noise

[camroc]

have the nct due soon and currently my exhaust idles in the high 90db's. just wondering if anyone knows some quick diy methods to bring the noise down, this is just for the nct as id rather not replace the exhaust just to pass

[drifthooligon]

You could fit a butterfly valve where the cat joins the centre section and run a cable up through the handbrake cable hole so you can close it and hide the cable under the capet, very useful for checkpoints aswell

[joeyfinneran]

That sounds like a good idea but whats a butter fly vavle ?
And how does it reduce the sound ?

[drifthooligon]

ìts bassicaly like a throttle body which when closed it restricts the air flow in an exhaust thus quietening it, my cousuin has this setup on his subaru impreza and without the butterfly valve it measured 124db and he didn't say what it read at with the valve in place bit it passed anyways

[davem]

A butterfly valve is a valve where a flap basically opens and closes, it's hinged around it's centre point.

I don't know, I think I'd be cautious by just adding a butterfly valve to the exhaust, partially close it on idle will reduce the sound, increase the revs without opening the valve further and you will be causing back pressure.

Most exhaust systems which have a volume control use a bypass type arrangement. A lot of guys with muscle cars have a valve, open it directs the exhaust straight out for volume, then shut them for street use directing the exhaust through the silencer. Others I've seen have an actuated BF valve so it opens with RPM but is quieter at idle. Or some race/street exhausts have a straight through section for track use and a quieter bypass option for street.

[drifthooligon]

But with the nct itd do just fine for the low and high idle, high idle is only 3500 rpm if im correct and it wouldn't be held there for too long so in my opinion i can't see any dangers with regards to using the valve, the bypass system is good but would it not be a fail if you'd alot of exhaust piping under the car ? That'd set of alarm bells for me now

[davem]

It doesn't have any extra piping really, the one I seen years ago had a section that just looked like a silencer, all you could see was one pipe in one pipe out. I didn't see inside it obviously, but my understanding - and that of the owner (it was fitted when he got the car) was it basically had the inlet pipe which split into 2 pipes inside it, one straight through, the other through the silencer section.

This is the Cutout kind

http://thumbsnap.com/s/4rFemKfe.jpg

this is the other type (not the one i've seen but same idea)

http://www.xforce.com.au/about-varex-re ... uffler.php

[drifthooligon]

Ah got ya, seems simple enough of a setup