Mufflers - Design Input

[GeeTR]

There's other factors too, hot and cold air bypass ratios, minimising turbulence, hot section design and acoustic materials in the ducts, but thats all kinda irrelevant to this topic.

Sweet, iv seen a few blackhawks that all seem to use a corrugated style.

rb26s13 - thats what i was suggesting, but multiple holes instead of just one works better at suppression.

[rb26s13]

Sweet, iv seen a few blackhawks that all seem to use a corrugated style.

rb26s13 - thats what i was suggesting, but multiple holes instead of just one works better at suppression.

if you want to try multiple holes you could look at possibly drawing it up and working out how many halfinch or inch holes you could fit in the flange

[Sydneykid]

Are you sure that the noise is coming from the exhaust? That exhaust system looks plenty silencing to me. I have had several experiences with race cars where fiiting extra mufflers made very little difference to the total noise. On one car we stuck some carpet underfelt around the ar filter box and it passed the noise test without changing the exhaust at all. On another car we retarded the ignition and advanced the exhaust camshaft timing and it quitened it down enough to pass. So the answer may not be in modifying the exhaust itself.

Cheers

Gary

[GeeTR]

if you want to try multiple holes you could look at possibly drawing it up and working out how many halfinch or inch holes you could fit in the flange

The ones iv seen, looks to have maybe just less then 50% surface area worth of holes.

[skylinekid]

Ok.

Been having issues getting my car past the EPA test, needing around 90dB to pass.

So far its pulled 93dB at this point, Benno/Racepace have done a top job, considering the car has a 3.5" exhaust on it… it’s a fairly big gauntlet that’s been thrown down

The car is no louder than a HSV, I cant even hear it @ cruise, but when you have a 5200rpm test point for the noise test, it’s a ripe pain to get passed as some of you will know.

I've been doing lots of reading on muffler design and so on to get my head around it all a bit better as to what could work, and what does not.

Plus having started reading i need to keep on reading as im finding it all quite interesting so ill fit it to my purpose also at the same time

My requirements.

1. Not worried neccesarily about performance at this point.

2. Just need the car to be at a legal level - which does mean dropping 3dB

I know there are a few engineers lurking, does anyone have some diagrams I could look at that?

Or even some links that don’t have too much jargon speak in them?

At the moment i have:

Compliance/stock size cat (for a GTR i think)

Also two mufflers, larger and a smaller

Im not looking for the quick fix like sticking a baffle/restrictor plate

A restrictor was put in right @ the end (jap exhaust style) and it didn’t drop the dB reading at all, so there must be some forces at work I don’t get, as logic would tell me it should be quieter but the meter says it was not the case!

This thread could probably help a number of people, i know there is someone in QLD having issues too

Cheers

Ash

5200rpm WTF....... im in queensland and ive been defected for xaust and the test limit was 3200..... they tried to do it at 4500 im like wat are u doin he tried to tell me it was a 4 cylinder im like nahh mate its a 6 count the exhaust runners.... he was stumped and confused??? then tested at 3200rpm with a shocking tune measured 104.5db lol oops

[Gts-t]

My trust PEII is about 85 or 86db at 5000rpm.

[saliya]

Hey,

I know you said you're not looking for a quick fix but a sieve plate where the cat flanges

are will get you to the right level and nobody's going to pick you up for being 3dB over

without a calibrated meter. Put the plate in, get measured, remove it. Cheap. Nasty. Invisible. Easy

Because you're at 3.5" you're going to find it very hard to shut that up to 90dB without

a restrictor. The law of diminishing returns, and all that - you might spend a lot of time

and money, and be not really any closer. Stuff that you can try:

* go do your test on the hottest day you can; your car is louder when it's cold.

They're supposed to apply temperature corrections for test conditions that are not 25 deg. but they never do.

Might make 1dB difference between a 5-10 deg day and a 30 deg day. No effect on flow, no cost.

* put a dump pipe on the outlet pointing it at the ground. It makes a difference; maybe

0.25 dB at the test RPM because of the test procedure. No real effect on flow, very cheap.

* replace both mufflers with ones that are as big as will physically fit (you have room

to go up a little in the middle; and a lot at the back). You might get 1 - 1.5dB out of that.

Probably have to be custom to get the biggest ones you can. This will affect flow a little.

Those three things might get you to 91-92dB.

Other things that will reduce flow (and noise):

* line the inside of the section just aft of the cat with perforated sheet rolled into a tube

(weld it in!) - that's basically what an unpacked resonator has in it.

Extend the perf for as long as you have a straight bit of pipe. This will have a small effect

on flow and noise but won't make your exhaust lower. You might get 0.25-0.5 dB out of it.

* replace rear muffler with one that has internal direction changes - problem is it will likely

have to be custom since I doubt you'll find one in 3.5" packaged to fit under your car.

This will affect flow noticeably, will be moderately expensive, but will look good and be permanent.

* replace rear muffler with one that has actual obstacles (e.g. steel wool) and direction changes.

When I did this to mine (4"), it was still too loud (don't have the number) but more steel wool

packing would have brought the numbers down.

As you've found there aren't a whole lot more places that mufflers can be fitted under that car.

Good luck, and make sure to let us all know how you go!

Regards,

Saliya

[Ronin 09]

yeah i'd like to see an offset rear muffler like this (brought to you by MS paint)

[R31Nismoid]

RE: baffles/plates etc

Reason I don’t want etc is it's been tried and did not work, result was still 92-93dB.

Hard to believe I know, I was as surprised as a everyone else involved the reading did not alter substancially… rather did not alter at all!

Going to try a 45 degree dump pipe al-a-VL-Jet spec style and see how that goes this time deflecting some of the noise away from the pickup point of the microphone.

Its definitely not picking up the noise from anywhere else. Injectors you can hear ticking but that wouldn’t be 93dB @ the rear end of the car.

[Devils_Advocate21]

would splitting the rear into two exhaust outlets of similar diameter (smaller diameter) x 2 outlets so twin muffler/small cannon, reduce noise? you get the picture or similar level, dunno what your rear of the car exhaust looks like

[Shaun]

trident - do you know how loud yours actually is?

Because if it isnt under 90dB then its not gonna help me a lot, and with a cannon i'd imagine it wouldnt be close

This is what i have now... so the answer be nope

Hey,

Did racepace make the centre muffler for you?

Ive got the excact same problem as you (ie, not wanting to attract attention with a loud exhaust), but im having trouble finding room underneath the car for a large (offset) centre muffler (R32 gtst). Im surprised that your centre muffler is not offset in design, as the change in direction within the barrel apparently has a large effect on noise. Most people ive spoken to say that the straight through perforated tube oval centre muffler has little effect on noise compared to an offset muffler.

Anyway, im waiting for x-force to bring out their 3.5 inch 'Varex' rear muffler, which is oval in shape and has an electronically controlled butterfly that redirects gasses within the muffler to reduce noise when needed. Its not ideal, but its an expensive process when you experiment with different exhaust designs, as you know.

Shaun.

[rb26s13]

RE: baffles/plates etc

Reason I don’t want etc is it's been tried and did not work, result was still 92-93dB.

Hard to believe I know, I was as surprised as a everyone else involved the reading did not alter substancially… rather did not alter at all!

Going to try a 45 degree dump pipe al-a-VL-Jet spec style and see how that goes this time deflecting some of the noise away from the pickup point of the microphone.

Its definitely not picking up the noise from anywhere else. Injectors you can hear ticking but that wouldn’t be 93dB @ the rear end of the car.

Jun make a muffler thats 3.5 inlet.. nice stainless unit refered to as "spiral BL" from memory.. it has to be the quietest muffler i have ever heard might be worth a shot? however they are not cheap

[Ronin 09]

Hey,

Did racepace make the centre muffler for you?

Ive got the excact same problem as you (ie, not wanting to attract attention with a loud exhaust), but im having trouble finding room underneath the car for a large (offset) centre muffler (R32 gtst). Im surprised that your centre muffler is not offset in design, as the change in direction within the barrel apparently has a large effect on noise. Most people ive spoken to say that the straight through perforated tube oval centre muffler has little effect on noise compared to an offset muffler.

Anyway, im waiting for x-force to bring out their 3.5 inch 'Varex' rear muffler, which is oval in shape and has an electronically controlled butterfly that redirects gasses within the muffler to reduce noise when needed. Its not ideal, but its an expensive process when you experiment with different exhaust designs, as you know.

Shaun.

shaun, i have a R32GTR with (what i'm aware) the first 3.5" RacePace exhaust with custom mufflers on it...

I'll try and get a pic

[Shaun]

shaun, i have a R32GTR with (what i'm aware) the first 3.5" RacePace exhaust with custom mufflers on it...

I'll try and get a pic

Yeah, Id love to see it. Apparently racepace are very good at designing high flowing and quiet exhausts. Pity im in Sydney.

Is it quiet? Is it on a single turbo?

PS: Its difficult to compare the level of exhaust noise between different cars with different turbo set ups.

For example, my RB26 with single turbo and 1.06ar turbine housing will always be louder than a twin turbo RB26 because the turbos act as mufflers themselves.

Shaun.

[Ronin 09]

Yeah, Id love to see it. Apparently racepace are very good at designing high flowing and quiet exhausts. Pity im in Sydney.

Is it quiet? Is it on a single turbo?

PS: Its difficult to compare the level of exhaust noise between different cars with different turbo set ups.

For example, my RB26 with single turbo and 1.06ar turbine housing will always be louder than a twin turbo RB26 because the turbos act as mufflers themselves.

Shaun.

2860-5s

trust front pipes, tomei manifolds

it's pretty quiet - all you get on the road is tyre noise.

is probably a touch over 90db though - most likely like R31Nismoid's

[Shaun]

^^^^Thats a great looking exhaust!! Exactly what im after.

Its interesting to see that the centre muffler is not offset either. I wonder if there is a 'U' shape in the middle.

So you bought the car with the exhaust on it, or did they make it for you? Theyre super pricey from what ive heard, but they work.

Shaun.

[STATUS]

Ash, I have used V8 mufflers in a few cars i could not shut up, hooker mufflers do a nice aero chamber that works well in sizes up to 4".

http://www.rocketindustries.com.au/descrip...?partno=HK21506

[Ronin 09]

trent would you use that as the centre or rear muffler?

[Ronin 09]

^^^^Thats a great looking exhaust!! Exactly what im after.

Its interesting to see that the centre muffler is not offset either. I wonder if there is a 'U' shape in the middle.

So you bought the car with the exhaust on it, or did they make it for you? Theyre super pricey from what ive heard, but they work.

Shaun.

i don't know if it's got a "U" inside it, but probably not - it's not that long.

they built it for the car last year - previously it had a 3.75" Trust Power Evolution II that did over 105db...

nasty.

[STATUS]

trent would you use that as the centre or rear muffler?

centre