Exhaust Recommendation

[R32Abuser]

Since visiting several exhaust places I have come across some conflicting arguments about what's best to quieten down my car to a legal level.

First of all, on the exhaust side of things I have the following:

• RB 25/30 using an R32 RB25DE head on a forged bottom end - 9:1 Static CR
  
• Std Intake/exhaust manifolds, valves, etc. etc.
  
• 256deg/8.5mm IN/EX Tomei Poncams
  
• GT3076R Turbo
  
• Bellmouth dump and 3" front pipe combined
  
• Highflow cat (tubular design) with a number I cant remember of cells
  
• 3" pipe back to a ~4" magnaflow resonator
  
• Magnaflow resonator onto a 3" inlet 3" outlet Jun BL 5" Oval rear muffler with a single 3.5" tip
  

In saying all this, the reason why I went with this setup was because 3 out of 3 well renowned/recommended exhaust shops here in Adelaide advised me to go with a middle resonator out to a big rear muffler.

Currently the sound volume is definitely not legal. I'd approximate it at around 96 dB at 3-4000 RPM.

This is comparing it to my older setup on my RB20DET (stock turbo, 3" turbo back, no middle muffler, rear cannon @ 97 dB).

The current setup is somewhat droney, loud, and difficult to be inconspicuous unless I'm in 5th @ 60kph doing 1700 RPM. In saying this, its a hell of alot quieter than it used to be when I first got the new setup back with the old exhaust system.

The consensus I get around here on the forums is to run as bigger middle muffler as you can, whilst keeping away from cannons/large tipped rear mufflers. I have recently read a recommendation to use as big a Borla/Hooker etc. muffler in the middle wherever it can fit.

Generally speaking, your typical middle/rear muffler (without going into brands) relies on absorption method to dampen/absorb the noise produced. Whilst resonators rely on destructive interference of sound waves to reduce noise. Is there a reason why I was recommended to use a resonator as opposed to a conventional big middle muffler? Is my centre resonator too small to work effectively in my current setup?

Any input is greatly appreciated as rather than spending the money AGAIN to help quieten it down, Id rather get it right...

Cheers,

David

[abr33]

I have a straight through 3 inch, with highflow cat, and a varex, open is 102 ish db, shut 77. It is engineered. Laws in sa may be different to nsw though. Keep in mind you cant use alot of power with it shut or bad shit will happen.

In my drive by tests i was 10 db lower than a hilux that drove past before me.

[R32Abuser]

Varex mufflers are in contravention of the ADR legislation unless fitted from factory.

R33's I believe had an option for a "valve" in the exhaust, but Im unsure whether this would warrant the use of a Varex muffler.

In any case, I have a 32, which didn't come with any "valve" from standard; so its a no go for me.

[GTSBoy]

Yuh, I'd tend to think that the engineer who signed off on the Varex probably shouldn't have. Instant defect in SA, and they're not as fussy in SA as in other states!

[black bnr32]

consider integrating a hemholtz chamber or a hidden apexi valve. dynomax makes an integrated mechanical valve muffler that may 'pass'.

also consider adding in a short dual exhaust section with an integrated x-pipe for sound wave cancelation purposes. another idea is a short section of unequal length dual pipes (more sound wave cancelation stuff).

i suspect you were recommended using a resonator (instead of a muffler) for sound quality rather than quantity.

[jangles]

Varex mufflers are in contravention of the ADR legislation unless fitted from factory.

R33's I believe had an option for a "valve" in the exhaust, but Im unsure whether this would warrant the use of a Varex muffler.

In any case, I have a 32, which didn't come with any "valve" from standard; so its a no go for me.

Is everything else engineered? Also current exhaust isn't 'legal' so why isnt varex an option?

[abr33]

varex is a grey area, he said in his eyes, theres no difference in me having a quiet exhaust on and going home and swapping to a huge loud one. Only the time factor. Also not having the controller kept in the car is a good idea. And the idea of an engineers certificate is to override affected ADR's I believe.

[AngryRB]

ive been having this same problem and have 3 1/2inch dump and system, ive just put a 3inch oval muffler on back and its suprisingly quiet, is a xforce muffler, decent size, the inside of it fish tails so must force the gas into the packing.

I am also interested to know what resonator or muffler to put in middle, the noise level is acceptable now and only really drones a bit at 2000rpm and in higher gears where its loading up slightly.

Ive noticed that an XR6 turbo's exhaust splits the pipe into two going into the cat, is this a good way off quietening it down and allowing good flow? you could have a cat that splits into a y section and then dual muffler at the rear or a massive muffler that has two pipes through it instead of just a single entry and exit, probably might burst the budget though.

[FordyR31]

My car has a full 3" turbo back exhaust and only has a cat and rear muffler. makes similar power to other cars with same mods except they have cannons... get a good rear muffler, mine is 84dB tested.

[ClutchBurndout-:(]

with turbos, bigger is better, so get the biggest you can offord.

[AngryRB]

no its not, bigger equals more noise,

Edited May 12, 2012 by SliverS2

[ClutchBurndout-:(]

no its not, bigger equals more noise,

well duh, you cant have your cake and eat it to.

Edited May 12, 2012 by ClutchBurndout-:(

[Piggaz]

no its not, bigger equals more noise,

Get decent mufflers!

[FordyR31]

Lol if the thread had been read he wants to reduce noise

[black bnr32]

http://www.supramania.com/forums/showthread.php?101230-Branch-resonators-ways-of-reducing-exhaust-drone

[ClutchBurndout-:(]

so he wants the fastest exhaust, with no noise? lol.

you can only have one or the other (usually)

ok this is what you want. Obveously you'r chasing power by looking at your setup, so obveously 3.5 or 4 inch is the go, or you can splurge on a twin system which is pretty much going to cost double. resonators (hotdogs) decrease drone, everyone should have one. baffled mufflers are going to slow you down, so go the big sports ones, and just get 2 of them. this should be a pretty quiet.

Edited May 12, 2012 by ClutchBurndout-:(

[R32Abuser]

[quote name=ClutchBurndout- ' timestamp='1336864848' post='6354154]

so he wants the fastest exhaust, with no noise? lol.

you can only have one or the other (usually)

ok this is what you want. Obveously you'r chasing power by looking at your setup, so obveously 3.5 or 4 inch is the go, or you can splurge on a twin system which is pretty much going to cost double. resonators (hotdogs) decrease drone, everyone should have one. baffled mufflers are going to slow you down, so go the big sports ones, and just get 2 of them. this should be a pretty quiet.

With regards to going 3.5 or 4 inch system - there isnt an immediate need to go this route for the power level I am chasing.

My current setup with the turbo I have has been shown to max out at around 300 ish RWKW on 98 fuel. I am currently making 281 RWKW on a lower reading dyno. Unless I change fuel to E85 (which I am not going to), the current exhaust setup has enough flow to suit. Going 3.5" is just unnecessary IMO.

A twin system is going to shut the car up, but its also going to cost the earth to replace the current system. From what I have seen, using a single setup, it is possible to get it down to legal levels or below. It's just a question of the muffler/resonator size and packaging constraints. Which is why I raised the thread to get some clarification on why I am being told one thing by an exhaust shop and reading a completely different argument on here.

Edited May 14, 2012 by R32Abuser

[scotty nm35]

To get rid of drone you would be best off tuning a Helmholtz chamber to cancel the unwanted exhaust frequency. Larger muffles will make the whole frequency range quieter but the chamber would target the frequency you want cancelled.

The maths behind reflective sound cancelling is quite complex so its best to make an adjustable length setup if you can. I doubt many muffler shops would help you with it though.

With regards to sizing, you would probably gain over 20kw going up to 3.5 inch at the moment, I gained 30kw but deleted the cat also.

[TiTAN]

just shove the biggest muffler or mufflers under it you can, 16-18" x 11-12" x 6-8" on the back with your existing middle muffler, if its not quiet enough make the middle muffler bigger, hotdogs don't do much in the way of noise reduction and your 5" rear muffler isn't what I would call a big muffler.

my 3" exhaust was legal (90db as tested by the rta and my engineer) and my 3.5" exhaust is just the same or quieter. the loudest thing when you put your foot down is the pod filter/Turbo.

[wolverine]

^^^ spot on