Exhaust noise solutions

[abently]

I'm interested in that software. I've been thinking of using something like Adobe Audition myself to sample my exhaust and work out sizing of resonators to cancel the prominent frequencies.

PM me your email and I'll send it to you. If you can host it on here even better as its only about 1mb.

[cambelt]

Does anyone know any companys in Brisbane that builds custom mufflers?
Motoline in melb got my 2 custom 3 in baffled mufflers made somewhere up brissy way (genie?). They cost me $480 each custom made for a MX83.
Dave

[the_random_hero]

Does anyone know any companys in Brisbane that builds custom mufflers?
Motoline in melb got my 2 custom 3 in baffled mufflers made somewhere up brissy way (genie?). They cost me $480 each custom made for a MX83.
Dave

We do, just did a nice stainless jobby for some GT40 Replica's. PM me and I'll send you some details.
My advice - biggest resonator you can get and at least a 14" straight-through muffler on the rear.

[Draven]

I also went through linden @ roadrunner for my 2j exhaust. People at the track complain that my car is too quiet for how fast it goes (which is basically what I asked for - quietest exhaust that wouldn't impede power production).

3.5", 5" metalcat, and 2 very large mufflers as close to the back as I could get them. Basically avoid straight through/cannon mufflers, get a good cat and 2 large mufflers, and she'll be sweet.

[cambelt]

What brand mufflers are they Greg , I gotted ripped with these custom jobbies at $960 , i still want it quieter .
Dave

[Draven]

You'd have to ask linden. I know they weren't especially cheap - not $960, but not cheap... I was willing to pay more for better quality.

[Talasas]

I'd like to hear more specifics as well, as I'm building a custom exhaust for my 4AGTE which will be 2.5". I'm basically after the same setup, as quiet as possible without too much restriction. Many of the 2" 4AGE exhausts I've heard are really loud yet the factory 2" SX exhaust is really good with a 2" diameter cat, ~12" long muffler, ~12" long resonator and a huge rear muffler. This is what I would like to use as a guide, however finding a resonator has been really hard. Would it be better to keep looking or just use another muffler? The two things that have been hardest to find in fact are a 2.5" resonator and a centre-in/centre-out muffler in 2.5".

[cambelt]

I wonder if linden would kindly chime in.
Dave

[TERRA Operative]

Absently, do you have any decent ways of working out the dimensions of resonators needed?

The formula below will allow you to work out dimensions, but it's only for regular Helmholtz resonators (like a bottle), not glass packed resonators with the perforated tube through the middle.

fc=(c/2π) x √(Sb/(L x V))

where

fc = resonant frequency
c = speed of sound
Sb = area of neck opening
L = length of neck
V = volume of resonator


Is there any way of calculating the size of glass packed resonator required, or is it a case of 'suck it and see'?

[Draven]

Talasas: if you're going 4a-gte, the turbo will quieten things down a bit anyways.. I'd just go cat + 2 mufflers (although to 4a is a bit of a drone-master)

[Cuzzo]

I run one hot dog and a rear muffler semi-flow.

Otherwise known as semi-offset?

Centre in one side out

[Gary]

I wonder if linden would kindly chime in.
Dave

fair call if he doesnt though

people make a decent living off this very subject, giving advice or spelling out how to do what it is theyre paid to do, for free, is very counter-productive.

annoying at times, specially when you need help with things like wiring, but its the way it all goes

[abently]

fair call if he doesnt though

people make a decent living off this very subject, giving advice or spelling out how to do what it is theyre paid to do, for free, is very counter-productive.

annoying at times, specially when you need help with things like wiring, but its the way it all goes

Unfortunately that's the truth. Its slowly but surely turning into a science though which is good.

The only problem still is that simulators like LMS Virtual Labs is still very expensive to buy and require a lot of training (mucking about) before you can even start to play around with it for what you want.

[forey]

with my 1j gt35R. its a 3inch turbo back/CAT there but bashed out/trust 3" in out offset muffler at the rear.
Its easy quiet enough putting around off boost, not sure how loud it is in top revs as the screamer blocks everything out haha

[abently]

Absently, do you have any decent ways of working out the dimensions of resonators needed?

The formula below will allow you to work out dimensions, but it's only for regular Helmholtz resonators (like a bottle), not glass packed resonators with the perforated tube through the middle.

fc=(c/2π) x √(Sb/(L x V))

where

fc = resonant frequency
c = speed of sound
Sb = area of neck opening
L = length of neck
V = volume of resonator


Is there any way of calculating the size of glass packed resonator required, or is it a case of 'suck it and see'?

I can scan something tomorrow and upload it.

Like I mentioned already, without getting too complicated with baffles, perforated baffles, empty areas, extended in/out tubing, etc, the following rules apply.

The larger the ratio between the perforated tubing raidus and muffler radius, the better sound attenuation will be everywhere.

The greater the rockwool density, the greater the sound attentuation will be everywhere also except for 0-250Hz range, where it is a little less.

After 25% perforation open area, the results are not much better. Offset perforated holes, ie distance between holes in y plane is less then distance between holes in x plane also offer additional improvements, only a little but every bit helps. Luckily the Truck muffler shop gets these as standard so its cheap.

So ideally, if you can fit a 10 or 12" wide muffler somewhere even if its only 10 or 12" in length, then I would do that. I think realistically you would need one of these packed lightly and then one at the end as big as can fit packed extremely dense (for the high-rpm exhaust noise).

You will find its the first order harmonic (<100Hz for most vechicles) that is the loudest (dB).

I will get the exact density numbers for you guys tomorrow also.