Managing exhaust noise limits - teased from Japfest thread

**mambastu** · 12-06-2005, 22:34

Finished my 'track' exhaust yesterday.

I've used a secondhand R32 Super Drager 3.5" centre section with silencer which PTS kindly modified so that its a straight swap for the intermediate section of the NUR Spec R. The Super Drager silencer is about three times the size of the NUR spec's tiny bullet silencer so we expected it to make quite a difference to noise levels but it only actually made 1db difference when combined with the NUR Specs tailbox (i.e 114db) ! Chris then made a new rear section using the biggest 3" Jetex oval silencer from DT which has surprisingly knocked it down to 98db, we thought we would probably have to go to three boxes.

The car sounds bloody boring now. Can't believe how quiet 98db is, sounds as quiet as a standard S13 and its taken a noticeable performance hit with the big silencer....grrrr.....twatty noise levels

I've got a trackday at Brands the week after GT Battle and after that the NUR spec's going straight back on.

**nene** · 12-06-2005, 22:57

Originally Posted by mambastu

The car sounds bloody boring now. Can't believe how quiet 98db is, sounds as quiet as a standard S13

Sounds like permanent hearing damage to me

It's interesting reading through this, though. I used to work in live sound reinforcement, where there's a limit of 120 dB SPL A weighted from the speakers. Which, quite honestly, is unbearably loud. We used hearing protection for health and safety reasons! The biggest PA I worked on ran off three phase mains, and could be heard a mile and a half away outside the building it was in!

That does take me to my point though, at those sorts of volumes, shouldn't you be using hearing protection?

**xR33** · 12-06-2005, 23:11

Originally Posted by John Bennett

As a nerdy aside, I was reading the Skyline service manual, and on one model there seems to be a system on the twin-exit exhaust to electrically shut one of the exits? Akyone know if this was for noise issues, and did it ever work well?

Originally Posted by mambastu

Yeah, it was fitted to some of the R33 GTS-T's but I've never seen it on a car over here. Some Mitsubish GTO's also have it.

Had one on my R33. Didn't really do a lot as it only worked on one side. Quite over-engineered setup for what it did really, with lots of cams and cable going from the boot to the exhaust.

**mambastu** · 12-06-2005, 23:33

Originally Posted by nene

That does take me to my point though, at those sorts of volumes, shouldn't you be using hearing protection?

Eh ?

It would be more of a problem if I had a seat behind the exhaust at 5300 rpm +
From inside the car its no-where near that loud.

**yeager** · 13-06-2005, 00:19

Originally Posted by nene

That does take me to my point though, at those sorts of volumes, shouldn't you be using hearing protection?

Sorry? I can't hear you

**nene** · 13-06-2005, 10:12

Something went past where I work off Rabans Lane on Friday, going (watch out for the sound effects

)

Originally Posted by Sound outside my workplace

vrrrooooOOOOOOM BANG VRRRRROOooo BANG vrrrrrrr pop pop pop-pop-pop-pop vrrrrrr pop-poppopopop

Was that you?

**yeager** · 13-06-2005, 10:41

Nope not me...

SM · 13-06-2005, 10:53

Good work, looks like I'll also have to invest in one of those big Jetex silencers.
Anybody have anyproblems with the big one being offset? (bottom one)
Has anybody tried the 630mm long one, not oval, non-offset. (second one)

http://jetex.co.uk/Jetexwebsite/univ...boxes3inch.htm

**kkydd** · 13-06-2005, 10:59

it looks like I will also have to buy one due to the police in the north of scotland having a zero tolerance on performance exhausts, my only hope it to make it as quite as a standard exhaust.

I was also thinking of enlarging the exit on my bung so that it will reduce back pressure a little but still quiten the system down.

**glens14a** · 13-06-2005, 12:15

I have a Jetex U447600R on my system 3" bore stainless steel 125mm x 250mm
It's made a big difference as I have a 4 branch/elbow and no cats

SM · 13-06-2005, 12:22

Originally Posted by glens14a

I have a Jetex U447600R on my system 3" bore stainless steel 125mm x 250mm

Sure? thats the 630mm version
U457600 is the 250mm one.

**glens14a** · 13-06-2005, 12:47

Originally Posted by SM

Sure? thats the 630mm version
U457600 is the 250mm one.

your correct it's a U457600R

**PhilMorrison** · 13-06-2005, 13:01

I fitted the largest of the Mild Steel universal Jetex box's last week, it's made the car far to quiet

.. It's not actually sapped that much power though. Definatly slower, but not to bad. To fit this box where the cat would normally, I had to get a bit inventive with the floorpan with the aid of a 20kg sledghammer

**sroberts** · 13-06-2005, 13:06

On a intersting note, it would be interesting to get dB reading for Dans titanium GP Sports exhaust. Its a single box system and its far far quieter than my nur spec and appears to not sap power.

Si

**Jolly F** · 13-06-2005, 13:25

Isn't anyone, especially people running big power concerend by changing silencers effecting the fuelling of the car?

People have mentioned a loss in power which will be straining things and car specific maps on stand alone management wouldn't compensate for this?

I've also got a concern of the screamer pipe which is loud. What can be done about this?

SM · 13-06-2005, 13:43

Feed the Screamer back into the exhaust somewhere further down the exhaust, or get a long 2" silencer for it.

Fuelling should only be effected on MAP-sensor equipped cars, then only nominally, the VE will only alter slightly.

**Drifter** · 13-06-2005, 15:30

Originally Posted by bren

We have a selection of silencers here now to try out

I have the Scorpian de cat from Bren. With Front Pipe, main cat and Apexi GT Spec I got around 114dB. With the Scorpian in it was the same, maybe 115dB

**kkydd** · 13-06-2005, 15:38

Drifter that can't be right, you are saying with the GT spec zorst with cats in gave 114dB, thats is louded than a jet plane on takeoff.

**mambastu** · 13-06-2005, 16:41

Originally Posted by Jolly F

Isn't anyone, especially people running big power concerend by changing silencers effecting the fuelling of the car?

People have mentioned a loss in power which will be straining things and car specific maps on stand alone management wouldn't compensate for this?

Can't speak for everyone else but I've noticed mine runs slightly richer in certain parts of the rev range with the new quiet exhaust so I'm going to re-map it slightly.

**Drifter** · 13-06-2005, 17:52

Originally Posted by kkydd

Drifter that can't be right, you are saying with the GT spec zorst with cats in gave 114dB, thats is louded than a jet plane on takeoff.

Not measured very technically though. 3000rpm and tested close to the tip with a *cough..cough* Nokia mobile phone

It certainly doesn't sound loud, just a very deep rumble, kinda like an earthquake

Thread: Managing exhaust noise limits - teased from Japfest thread

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