Name that exhaust peice!
 

Alright... directly behind the muffler, a little further back than the middle of the car, there is an exhaust component which rattles like a mofo. What is this component? is it a resonator, or another catalytic converter? Can i replace it with something universal, yet equivalent, while retaining the emissions standards? Thanks
-Ross

its the 3rd of 3 CATS

argh, i feared that's what it was. how about my other questions? how easily can it be replaced with an aftermarket unit?

Sounds like you're talking about the resonator (SOA primary muffler). It's usually the one to make noise. Take it to a muffler shop to be sure. I can be replaced with a straight pipe or a suitable glass pack if you want to preserve the exhaust design. :D

picture --> http://www.subaruparts.com/diag/?mod...category=440-A

Sounds like a resonator to me. The car does have 3 cats but usually the noise comes from the resonator after the cat. For most people, it looks like a cat. I don't know what the deal is but on the 94s that I owned, resonator had gone south and I had to replace it with a straight pipe. 92 is running great. (knocking on wood). Although the striaght pipe mod only costs me 20 bucks.

Lwin

ARGH... speedy's told me it was a resonator first, then he told me it might be a cat... but by what the two pictures show, its just the primary muffler. So I guess i'll replace that with a straight pipe tomorrow
Thanks guys!
-Ross

RESONATOR rattles
 

I had mine removed a year ago. It's loss has had no ill effects. Most muffler shops want to replace the whole system. Shop around and you'll eventually find someone who knows that it's just a resonator and will cut it out and weld in a piece of straight pipe. My exahust system is still going strong at 211,000 miles. Minus the resonator, that is.

What does the resonator exactly do? Is there a weight difference b/w that and a srtaight pipe? I'm thinking about exchanging mine with a straight pipe now, too...

-scooch

"The extensively tuned system resulted in a low back-pressure, racing type exhaust design..."

and

"The overall design not only enhances exhaust efficiency contributing to the high output of the engine, but it also creates a pleasant, very sporty exhaust note."

Oh my oh MY this is lame. Brand new SVX had the exhaust note of a reedless clarinet. Racing type exhaust design, yet no manual transmission? Ah, sure. It appears that whoever was in charge of SOA PRODUCT PLANNING in March of 1990 was not at all up tp the task. The numbers on the diagram were obviously done by someone with little to no training in drafting, or the graphic arts.

Seeing this (http://www.subaru-svx.net/forum/atta...=&postid=47622) makes me wonder what delightful products the fools who failed at marketing the SVX have killed in the crib recently.

Please show us more! :)

Removing the resonator????
 

Hi Scooch.
The effect, of removing the resonator and useing a straight pipe, would be a tapering off, of the torque curve after about 4500. That top end rush that gets us overtaking quickly and safely would be lacking somewhat around 5500 to 6500. This is because of the pressure rise in the header pipe, acting back into the cylinder to foul the inlet charge when the valve opens,

Not having the resonator in place means that the exhaust pressure plug has to travel down to the rear muffler to expand, so the ambient pressure at the exhaust ports will rise earlier in the rev range than it was designed to. Of course the amount that you notice the loss, depends on how much time you spend on the razors edge.
The best fix for a resonator rattle, is to replace it with another one, the same as you would do with any other part that was faulty.
It does not have to be a Subaru replacement, any resonator or glass packed that will fit, is better than nothing, the bigger the volume the better.
This is a bit involved but it's probably why it's function is so misunderstood
Harvey.

Exhaust system design.
 

Vern, I do agree with your thoughts on the exhaust note. As agressive as the passing of wind at a dinner party.!:rolleyes:

But I do agree with the discription of the design and function. This is a very well thought out system. I don't think it could be improved and still fit under the car. The rear muffler is the only section that may be altered to change the sound, without degrading the engine's output.

This is how the exhaust system functions.

The SVX as you know is a flat six, of two banks of three cylinders. Each bank has it's own three branch header leading into a single pipe, this joins with the pipe from the other bank of cylinders to continue down to the muffler.
The engine has a 120 deg crank, this means that for every revolution (360degs) the engine fires three times, 120degs. apart, two revolutions(720degs) to fire all six cylinders. If we look at one bank only for simplicity, we have three cylinders that fire 240degs apart.
You would know that the exhaust is expelled during the exhaust stroke by the piston rising pushing the gas out of the cylinder. Unfortunate this is not quite the case, when the exhaust valve opens 55degs before bottom dead centre on the end of the power stroke, two things happen. First a positive sound wave is released (like popping the cork on a bottle of bubbly) travelling at about 1700ft/sec to the end opening of the pipe where it is replaced with a negative pressure wave which travels back up to the valve.
If the pipe length and the engine rpm match, this negative pressure will enter the combustion chamber in time for the inlet valve to open thus inducing the inlet flow.
The other thing to happen when the exhaust valve opens at the end of the power stroke, is a gas pressure of about 60 to 70 psi. is released this "gas pressure plug" travelling at about 300ft/sec exits the cylinder under it's own energy. This has to be out of the cylinder by .the time the piston starts to rise on the exhaust stroke otherwise we will use power to push it out.

Also if this pressure is even say 4 or 5 psi the rising piston will compress this gas in time for the inlet valve to open forcing it back up the inlet tract fouling and heating the inlet charge.

Well where does the resonator fit in, or expansion chamber to give it it's right name. If we look at our bank of three cylinders firing every 240 degs apart, this is about 20mil/sec, and the gas plug has time to travel down the pipe and dissipate, but when the rpm increases to 5or 6 thousand the time is only about 6.6mil/sec, to short for the gas plugs to push the long column of gas right down to the end of the exhaust pipe, for while this pressure exists in the pipe it will be acting on the piston robbing us of power.
So the answer is clear we need a shorter pipe for the higher rpm. Not easy to do on a car but we can put a chamber on the pipe up closer to the cylinder where this gas plug can expand into and have the gas plug and the sound wave act like they have reached the end of the pipe . This drops the pressure which bleeds down out the tail pipe, in time for the next gas plug 6mil/sec later.
I think you will now agree that the resonator does perform a vital function in allowing the engine to deliver good power right up to the red line.
At least that 's the way I see it.:cool:
Harvey.

Go Gettim, Harvey :eek: :p :D

for oab---
"OHH!! I see!!" said the blind man to his deaf wife...
as he fell down the stairs..

Re: Exhaust system design.
 

Oh yeah? :mad: Well, what about, ah... er... Oh look at this shiny keyring. So shiny, and it has keys on it. I like shiny things.

(about how I am feeling right now after reading your well done post) :D

Re: Re: Exhaust system design.
 

Vern,you could try polishing the stainless steel muffler, till it shines.
That must be worth at least 10 to 15 hp, and every one would be able to see your shinny rear end. :D
Harvey.