exhaust note, what are the factors?

[BRZPDX]

so after going catless/FI, my car definitely lost the deep exhaust note. At under 4k RPM, the car got quieter (less drone) than previously with the catted stock header and being N/A. I've heard the turbo muffles the sound a bit.

I wouldn't call my car raspy, but after 4k when boost kicks in, its deafeningly loud.

Current exhaust set up is:
Custom made EL header/OP, catless
Invidia 2.5in catless front pipe
Invidia 2.5in resonated mid pipe
Invidia 2.5in axle back exhaust

I have heard the thickness of the wall on the exhaust can contribute to rasp. Thankfully the Invidia does not seem to rasp at all. The Hemoholtz resonator I heard was only for cabin drone.

So my question is, which exhaust has a thicker wall that prevents rasp, and what do you guys suggest to keep the noise level down at WOT? From my personal experience, uncatted Perrin 3in setup had significant rasp. I'd like to go 3in, but this automatically means louder? Can you weld more resonators in without causing further restrictions? Do the wall thickness of the exhaust really help keep the noise low/deep? Is it impossible to keep the noise level down without a cat or is it a muffler mechanism?

[JustBoostin]

When it gets deafeningly loud, that is most likely the wastegate you're hearing, especially if it is vented to atmosphere. Easy fix if that's the case. Get the dump tube recirculated into the exhaust.

[BRZPDX]

Originally Posted by JustBoostin

When it gets deafeningly loud, that is most likely the wastegate you're hearing, especially if it is vented to atmosphere. Easy fix if that's the case. Get the dump tube recirculated into the exhaust.

I hear the dump tube separately for sure. The wastegate more sounds like "psshssssssssss" and my exhaust is more like "vrrooommmmBBBAAAAAHHHHHHHHHHH!!!"

[wparsons]

I think you're mixing up the BOV and the wastegate... if you're running an open dump on the wastegate it'll do just what you're describing as soon as it reaches full boost. The BOV will make a pssshhhh noise whenever you back off the throttle.

Skip to the end of this for the open WG noise:

[ame="http://www.youtube.com/watch?v=_oBY2Y3mjHs"]Evo IX Open Waste gate external Dump in Tunnel - YouTube[/ame]

And this for BOV noise:

[ame="http://www.youtube.com/watch?v=HblCEQXQ8Q4"]hks super sqv (sequential blow off valve) sound - YouTube[/ame]

[BRZPDX]

I'm a car newb, but I know the wastegate dump noise is only at throttle, and the BoV is when the throttle body shuts (letting off the pedal) and make a noise when venting to atmosphere.

Yes I do hear the wastegate separately from my exhaust note. One is "Pssssssssssssssssssssssssssssssss" not "Pshhh" and my exhaust note is "vrooommmm(below 4k) BAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHH (past 4k)". The whole time the wastegate is "ssssssssssssssssssssssssssssssssss".

Fuck it I'm gonna GoPro it when I get a chance, this Pssss Psh BAAAAHHHHHHHH typing is not working.

Back on topic, to keep exhaust noise levels down, choosing a right axle back versus adding more resonators will decrease noise more efficiently correct?

[StormTrooper]

Basic concepts only: muffler does what the name suggests and lowers sound volume. Resonators remove or reduce certain frequencies. Wall thickness and material type will affect both but especially rasp or metallic sounds.

And coming from experience wastegate dumping to atmosphere is crazy loud. Like hear from miles away loud.

[wparsons]

Before you go record it, are you running an open dump on the wastegate?

The wastegate won't make a psssssssss noise, that's the turbo spooling. Did you watch the first video I posted, that makes the exact kind of noise you're describing and that is an open dump wastegate.

*edit* - found the pictures of your kit, it's 100% the wastegate dump making the noise you're describing.

Turbo spooling makes the pssssssssss noise
Open wastegate dump makes the baaaahhhhhhh noise
and since you're not running a BOV, there's no psssshhhhh noise.

You can put any exhaust you want onto the car, but until you merge the dump pipe back into the exhaust you'll never fix the noise.