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Thread: Managing exhaust noise limits - teased from Japfest thread

  1. #21
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    Quote Originally Posted by yeager
    on topic?
    Use a valve, or get burned hands

    Decat silencer should make a little bit of a difference, but I find at full chat it just can't cope with the volume of gasses :totallydeaf:

  2. #22
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    Quote Originally Posted by JackaL
    Use a valve, or get burned hands
    Not keen on the ristrictiveness of a valve. I would be changing the silencer at the circuit, I would know the noise level before hand and throw on the relavent silencer the night before. In all honesty I don't think i'll need more than one because I think the combination of decat silencer, decat pipe and bung would give me some variation on noise.

  3. #23
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    Quote Originally Posted by yeager
    Not keen on the ristrictiveness of a valve. I would be changing the silencer at the circuit, I would know the noise level before hand and throw on the relavent silencer the night before. In all honesty I don't think i'll need more than one because I think the combination of decat silencer, decat pipe and bung would give me some variation on noise.
    Ah

    Personally I can't see how a bung and valve differ in restrictiveness. They both reduce the diameter of the exhaust pipework to create more back pressure, and therefore reduce volume.

    The only difference I can see is the bung is right at the end of the exhaust, so the engine can fill the pipework with gas before it becomes restricted - whereby with the valve it only has the pipework prior to the valve to fill before it becomes restrictive.

    How about fitting a valve at the last join in the exhaust, and running without a bung? At full-open, a valve would be very unrestrictive (compared to a bung). Otherwise, fitting the largest possible silencer would be the best option. I don't think a silencer could sap much power - so I wouldn't want to be changing them all the time when one would suffice :i'malazybastid:

    EDIT: Or buy another NUR back box, and plumb in twin back boxes - one per side

  4. #24
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    Back off topic - I saw you driving the pink machine to work on Friday Si I was in the Pug, and too tired/slow to flash you before you'd gone...

    You were nearly as late as me!

  5. #25
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    a mate just tested his dB level of the Megan Cat-Back on his S14 - with bung in and CAT he got ~78dB on a drive by measurement - this is with 0.8bar of boost on the stock engine though... regulations for street (we don't have any tracks) are so mad I'd need to hit a max of 76dB with the S13 to get trough which is ridiculous as about every other new or old sportscar is louder... but I'll have to match the original item...
    anyone fitted the complete silencing setup bren offers (i.e. donwpipe silencer etc)? and took a measurement?

  6. #26
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    Quote Originally Posted by JackaL
    Back off topic - I saw you driving the pink machine to work on Friday Si I was in the Pug, and too tired/slow to flash you before you'd gone...

    You were nearly as late as me!
    I saw you coming down the chesham road onto the 413 in my s13.

  7. #27
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    Quote Originally Posted by ATrull
    I saw you coming down the chesham road onto the 413 in my s13.
    With the black headlights? Ah, think I saw you too

  8. #28
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    Quote Originally Posted by JackaL
    With the black headlights? Ah, think I saw you too
    twat she is looking good!

  9. #29
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    I got 106Db with my Nur Spec and 2 3/4" downpipe. I threw the bung in and got 105Db although it's worth noting that I was parked a car's width closer to the wall for the second reading. With Pointblank's massive bung I got 90Db although the power suffered

  10. #30
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    Quote Originally Posted by ATrull
    you haven't heard the dissapproving shouting from my neighbouring streets when I fire it up at night without the bung
    Lol, and nor have you

  11. #31
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    Quote Originally Posted by Jez
    I got my silencer from Merlin Motorsport - you can view the range of silencers here: www.jetex.co.uk, in the universal parts section.

    I went for the biggest 3" silencer they do (Its a straight through design, so shouldn't impede flow too much) with a cat back 80mm Nur Spec. Never had a prob with noise so far.
    Why did you choose this make? Is the construction good? Did you slot the silencer into the same space an S14 decat pipe would go? If so, which unit did you get?

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

  12. #32
    S13 + 2bar = 475@wheels bren's Avatar
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    I said it would crack and said that the seam should be welded before it went on the car. Theyre pants and we are sending them all back.

    Bigtone got a Jetex silencer and he was still over the limit.

    Im going to order one Jetex U307600 and one U447600 (if it looks like it will fit) tommorrow and see if I can stick one into the front pipe (S14) and the other where the current (2.5") decat silencer lives.

    The last time I fitted one of our larger decat silencers it dropped the db reading by 7, on Sat it dropped it by just 4

  13. #33
    Flamethrower Jez's Avatar
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    Quote Originally Posted by yeager
    Why did you choose this make? Is the construction good? Did you slot the silencer into the same space an S14 decat pipe would go? If so, which unit did you get?

    http://jetex.co.uk/Jetexwebsite/univ...boxes3inch.htm
    I got the largest box at the bottom of that page. I got that make because I couldn't find anywhere else that did 3" silencers on their own. They're fairly well made and coated in tough paint/plasticy stuff that hasn't burnt off. There may well be better alternative but at the time that met my needs

    I made my own front exhaust section and incorporated that silencer into it. Its a bit big and my exhaust hangs down a bit low. Not really a problem. I don't think any of the Jetex range would be a direct swap for any nissan parts, so you'd need fabricate something to get it to work.

  14. #34
    S13 + 2bar = 475@wheels bren's Avatar
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    Its a pity that the holes are offset Did you fit that where the original cat would have sat?

  15. #35
    Flamethrower Jez's Avatar
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    Quote Originally Posted by bren
    Its a pity that the holes are offset Did you fit that where the original cat would have sat?
    Yeah, roughly. The fact that the holes are offset actually helps. Having said that - the section of the exhaust that I made is quite bodged...

  16. #36
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    Quote Originally Posted by bren
    I said it would crack and said that the seam should be welded before it went on the car. Theyre pants and we are sending them all back.
    shh i wasn't going to mention where I got it from! We didn't have time to do the welding and it seems we never needed the darn thing in the end! But Wild Trax is going to be very very concerned about noise...

  17. #37
    S13 + 2bar = 475@wheels bren's Avatar
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    Ive got to sort something before the weekend as we are at Croft on Sat so Ill post up the results

  18. #38
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    I saw a few cars going round the track - notabley the 240Z's - with extra silencers attatched to the end of their exhausts. they look a little dorky, but are easy to stick on for track days and do their job.

    Haven't looked for anywhere that supplies them, but I assume they are just normal silencers like the ones in the link Jez posted. Would have to have some form of adaptor pipe made up before being able to attatch it to the jap spec exit pipes, but could be a usefull idea?

  19. #39
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    With reference to what Angelus posted.
    Those noise baffles are completely useless for our cars. I put one on at Bedford, but first lap out i got black flagged...not worth getting at all. They seem to work on NA cars though.

    btw i've got Apex Single box cat back, de-cat and front pipe all courtesy of Bren.

    Cheers,
    Las

    *edit* also got black flagged at Donnington on Satuday..noise increased 1st lap to 100dB then 101dB then 102.5dB...nice comment from the steward..."yeah mate, we've had a problem with noise on these skylines...."
    Last edited by Lasitha; 24-05-2005 at 12:20.

  20. #40
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    Ah bollocks....

    Just been down to Goodwood to have my car noise tested. Very friendly and helpful people down there

    I mentioned that my car had a Skyline engine in it and they said that they have a lot of problems with Skylines and noise levels. An early bad sign was the guy shaking his head as I drove it up to him.


    Measured at 5300 rpm I achieved.....115 db

    I think I almost broke the fookin sound meter

    I have a NUR Spec R cat back rear system with a custom built twin 2.5" into 3" front pipe. The odd thing is that if anything it actually sounds quieter inside the car with the bung out than it ever did with the same exhaust on the CA.

    Jez, any idea what db's your car was before and after you fitted the additional silencer in it ?

    Ah bugger, not sure that I'm going to be able to get that down to sub 105 levels even with an extra silencer and to be honest it sounds so nice with the current setup I don't really want to. Silly low noise limits

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