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Quiet 3" System Is There Such A Thing

dog25t

By dog25t,
in Engines & Forced Induction

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TiTAN Grand Master

TiTAN

Posted
Posted

My soarer is loud as f**k with its 3.5" system

Has a big hooker aerochamber at the back and a custom mid muffler (its small cause f**k all room with a 3.5" pipe)

What mufflers are you guys using on the quieter systems?

4" dump, 3.5" cat, 3.5" mid muffler, 3.5" massive 18x12x6 rear muffler.

Both just off the shelf straight through glass packs from an exhaust shop, did a little shy of 400kw just fine on a 35r years ago, dyno sheets somewhere in the rb30 threads I believe.

Kinks Grand Master

Kinks

Posted
Posted

Low frequency components (~120Hz) seem to be the main frequencies transmitted into the cabin and the source of exhaust drone. An uninterrupted exhaust diameter from front to back (think 3" straight through) seems to be prone to resonances around low frequencies. The only way to break up the low frequency resonance is to make the length of the constant 3" section shorter. The way of doing this is by changing the exhaust diameter in the middle with a full size centre muffler. This is why basically every quiet exhaust has a full size centre muffler. A hotdog resonator in the middle won't do much, they are too small to change the pipe tuning.

I had a Fujitsubo catback in my R33 and it had full size centre and rear mufflers, very quiet system. I'm about to buy something very similar for my R34.

discopotato03 Grand Master

discopotato03

Posted
Posted

Mine is 3.5 to the back of the cat and 3 through two large strait through mufflers to atmosphere .

One thing you can do is to put a "soft" part in the system to isolate engine vibration from the exhaust system . Most of you would have seen those spring loaded carbon ring and cup joints many transverse front wheel drive cars have . Because the across car engine rocks back and forth under acceleration (torque reaction) the exhaust can't be rigid or it'll act as a tie bar .

This clever joint allows engine movement whilst staying sealed , it also isolates to a degree engine noise and vibration .

Big diameter tube is very rigid and tents to transmit lots of vibration and noise into your cabin . I got my one off exhaust fitted with one of these spring loaded cup joints behind the cat and roughly where the gearbox exhaust hanger is . That way the front of the exhaust system is supported the length of the rigid engine and gearbox but allows movement south of there .

A bit of mucking around but it does work .

A .

XGTRX Veteran

XGTRX

Posted
Posted

Mine is 3.5 to the back of the cat and 3 through two large strait through mufflers to atmosphere .

One thing you can do is to put a "soft" part in the system to isolate engine vibration from the exhaust system . Most of you would have seen those spring loaded carbon ring and cup joints many transverse front wheel drive cars have . Because the across car engine rocks back and forth under acceleration (torque reaction) the exhaust can't be rigid or it'll act as a tie bar .

This clever joint allows engine movement whilst staying sealed , it also isolates to a degree engine noise and vibration .

Big diameter tube is very rigid and tents to transmit lots of vibration and noise into your cabin . I got my one off exhaust fitted with one of these spring loaded cup joints behind the cat and roughly where the gearbox exhaust hanger is . That way the front of the exhaust system is supported the length of the rigid engine and gearbox but allows movement south of there .

A bit of mucking around but it does work .

A .

Is it the same as a normal flex joint?

discopotato03 Grand Master

discopotato03

Posted
Posted

Noise reduction is more important than ever with the laws being the way they are , which is why standard cars now sound like vacuum cleaners .

That "soft joint" also takes a lot of load off your turbine housings bolts/studs and very likely the manifold itself .

A .

discopotato03 Grand Master

discopotato03

Posted
Posted

No they are actually better things than the bellows type ones with the braided wire outer covering . The braided ones don't like really high temps and the word on the street is that they expand inwards creating flow restrictions .

With the spring loaded "cup" joints the only things that can fail are the carbon ring or the two bolts and springs but I've never seen the fasteners or springs give up . The other thing is that they are really simple to take apart and the usually the only consumable part is that carbon ring - which if in fair condition goes straight back in .

I had to insist the exhaust place that made my system fit one but it was well worth it . Truck exhausts sometimes use these kind of joints so big bore parts shouldn't be hard to get . Some better exhaust places may even have the press dies to make them .

The obnoxious hum/buzz/drone in aftermarket exhausts is often the exhaust pipe and mufflers vibrating/resonating particularly if the engines torque reaction is being restricted by 3 or 4 metres of big bore tube . The engine and gearbox mounts are there to dampen engine/trans NVH , but hang a long rigid tube off something solid like a manifold and or a turbo and you can expect noise and vibration issues .

My old Subaru RX Turbo had a 3" dump pipe and 2 1/2" behind the middle muffler , think 1800cc flat four with small port prehistoric heads and a little GT2554R turbocharger . In legal rally trim (Grp A cams/pistons/computer/exhaust) these engines put out a great snappin 190 hp at the flywheel .

Really that exhaust was too big for what I was doing but with straight through mufflers and one of these joints in the factory position it was NOT noisy - at all .

I'm not saying that these joints are a magic bullet but together with big can area straight through mufflers (no baffles) you can have an exhaust that doesn't wake the dead or irritate your cars passengers .

A .

  • Like 1
AngryRB Grand Master

AngryRB

Posted
Posted (edited)

How much can the "cup" joints flex/move ? Wondering if they could be used to help line up segments of the exhaust ( making home made exhaust here.. lol )

Anyone used this style flexi joint part? post-70965-0-07561700-1466814319_thumb.jpg

Edited by AngryRB

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