Hi guys,
I'm writing a bit to give people a heads up on a noise reducing device I recently installed on my R32 GTR.
Its called a butterfly valve! My mate brought it in a 3 inch size from Autobahn (I hate that f**king store so much) for around $200 and never fitted it too his car, so I bolted it into mine. It is a circular plate which can rotate to restrict airflow in the exhaust system, I found a photo of one for sale on here, and have added a link too it below but a lot of exhaust stores can get them in, but 3" is the largest size i think.
http://www.skylinesaustralia.com/forums/Wo...alve++butterfly
Anyway this is his pink fluffy velvet background picture, from his add but you can see the butterfly, the section of exhaust you bolt into your exhaust and the cable and lever to control it all.
I have a 4 inch exhaust after the gutted cat (it came that way) and I simply put the valve in line with the cat just after it then ran the cable up through the gearstick boot, but you could use the eyelet for the CAT exhaust sensor, then put the control lever on the right kick panel on the drivers side, just under the bonnet release, this keeps it out of view of the police if I get pulled over as they apparently can ask you to open it up for noise testing.
The valve when fully shut its diameter is slightly smaller than the pipe it sits inside so it doesn't completely restrict the airflow but does create a lot of back pressure. Now at idle you wont notice this much, ever revving the engine stationary wont make a huge difference, but under load when most open exhausts are noisiest it really does make it a lot quieter, great if you want to pass a cop in a 50 zone on the side of the road, or you live at the top of a steep hill.
You have to be quite mindful that with the increased back pressure your turbos will not spool up anywhere as fast or easy, and infact if you try kick the arse on the car when it is shut you could potentially blow a gasket as the pressure finds other ways out of the exhaust system, not a problem for me because I had a not standard cat converter on my car and had to trim the flanges on it to fit the cat with an angle grinder and successfully cut a couple of holes in the cat (yes I'm getting them welded next week).
The added bonus of this seams that the engine seams to be running smoother on long cruises;
I think this is relative to valve overlap which is basically how part way during the combustion cycle the intake and exhaust valve are both open, without back pressure to hold the mixture in the cylinder I seamed to be running a little rich at low to mid RPM when the turbos weren't boost like when I'm driving on the highway, something closing the butterfly once I'm at cruising speed has almost completely fixed!
Anyway I can boast enough about this device and the hassles it has already averted for me and hope this helps some of you guys, if anyone needs some help and you post a question and I dont reply please PM me.
Dave