Muffler centre pipe investigation - Bit of a surprise!

[cpitts]

After some hacking and slashing, I've come to the conclusion that the factory centre and Y pipe, aren't that bad! Now here's some justification for those crazy and completely opposite view to all performance tuners (typically exhaust retailers)!

Firstly:
The centre muffler is simply a resonator. Even better than that, it's a straight though pipe with a few holes drilled in it AND VERY dense fibreglass packing.



And when you pull all the stuffing out, you can see more of what I mean. There's no chambers, just re-enforcing for the can itself. So it'll always flow air pretty well. This straight through setup also explains why you hear crackle on over-run, there's not a lot between the dump pipe and mufflers to extinguish it.

Here's it empty:



Will be interested to hear feedback.


Oh, and Tangcla, sorry for killing it on ya. All in the name of science.

UPDATE:

Further to this initial investigation, I wasn't entirely convinced that it could be _that_ performance oritented, so I had a few more questions to answer:
1. I wonder if there's some form of diamter restriction in that centre muffler pipe, even if it is perforated. Answer: Nope, it IS straight thru!!!


2. Why is there a bump in the exhaust just before the join. Why's that there, is it to do with the split or pipe joins??? Answer: Nope, it looks like it's there to either create turbulence to even out the airflow to each muffler, or it's just there as a pure restriction to help slow things down. Either way, it's not a huge reduction in pipe diameter.


3. Just how poorly made is that pipe split? Surely it can't be that good being made to a cost, not a quality, can it? Answer: It looks pretty damn good actually! Split is perfectly centred, while it's not knife edged, it certainly is rounded and sufficiently thin. Not bad over-all!


Now I'm happy that the standard pipe is sufficient for what I'm doing. Diameter is big enough, split is smooth enough and mufflers will be offering little restriction, the big question is how restrictive is the stock dump on the stock turbo. I know it'll change spool up, but I'm wondering if I can hit turbo peak power without a dump change . . . . . . . I could in a WRX . .. . .

[ultrablue]

nice find

[tangcla]

Oh, and Tangcla, sorry for killing it on ya. All in the name of science.

lol, it's okay. so I guess I don't really need a different center pipe then

[moggy]

lol, it's okay. so I guess I don't really need a different center pipe then

I just wouldn't use that one!!

Bob.

[Arith]

Great investigative work, Craig! Thanks for the donation Clarence.

Craig, you gonna gut this one to use alongside your gutted mufflers?

[EJ25]

LOL at first I thought it was some animal.

[Arith]

LOL at first I thought it was some animal.

LOL! Yeah, I was thinking "Gez, did Craig stuff a small dog into that centre resonator?"

[cpitts]

The plan was to be that I'd open this up, it'd be a massive maze of rubbish (like the rest of the Subaru muffler items). I'd gut it, reseal it and then fit it up with the gutted mufflers for even more airflow from the 'stock' system. Looks like I'll not actually bother because it's pretty much an ideal scenario already. A straight through pipe from one end to the other with a few holes stamped into it. With what I was going to do to it doesn't really add anything to the setup other than to remove the sound deadening/packing.

I knew this wasn't going to be the case the moment I did the first cut along the muffler and saw fibres inside.

I brought this centre pipe of Clarence so he doesn't need to fix this up to make his car work again. Expendature in the name of science, just a bit more maintenance as far as the ATO cares.

[GTSPECB STI]

Craig I applauded your investigative efforts.

edit...that hair in the resonator looks disgusting and makes me ROFL thanks for sharing.

[sundayDriver]

LOL at first I thought it was some animal.

I thought the first line would be "I found a skunk living in my centre pipe."

[OzSTi]

Great work! I applaud the systematic, evidence based approach you are taking to modification.

Would someone define the difference between resonator and muffler in terms of design and function.

[cpitts]

Thanx for the feedback OzSti. This approach is the ONLY way to prove what you're doing is either right, or a waste of time/money. It's the scientist and engineer coming out in me.

As for the 2nd part of the question, this is how I see it:
Resonator:
Simply a chamber that change diameter of the pipe to change the resonant frequency/speed of the airflow, resulting in acoustic changes but nominal airflow disruption.
eg: the pic above, the pipe is straight through BUT the holes in the pipe let the exhaust pulses get pushed out into that dense fibreglass padding, removing the pressure waves from exhaust gas and ultimately from the rest of the system (including @ the tip where the noise comes out)

Muffler:
It's a chamber that the air goes INTO from one pipe and is then pushed through a range of pressure chambers in an effort to cancel out as MANY of the uneven engine pulse frequencies and send smooth clean air out of the muffler outlets which means nice quiet muffler dB readings.

Have a read of my muffler gutting thread for example pics. Mazes, mazes, mazes.....

[Sentinel]

After reading the topic and then seeing that first pic - I thought yep, that's a surprise alright, Craig's found his toupee in his exhaust!

Nice work mate!

[cpitts]

<snip> Craig's found his toupee in his exhaust!

Toupee!!! The amount of fluff that came out of that would shame most 80's glam rock bands! I could have some sensational teased up 80's rock god hair!

But that's not high on my list of mods.

[adz2.0r]

Jesus for a second there i thought you had sucked up a cat. hahaha