Another Question For You

I have seen this talked about alot, and I was just wanting to know how many of you really think that the Resonator is the main cause of the "rattling" noise that so many SVX's make? I really need to get rid of this, although i'm sure that THIS problem will have to wait until I get rich and can fix the other problem I'm having. Let me know.


Thanks, Allen

[svx_commuter]

Allen,

The rattle noise on my car is the heat shield between the header heat shield and the Y intersection. I let it rattle. Lets me know when the car is warmed up because then it stops.

[Seraph]

Originally posted by SVXtremist
I have seen this talked about alot, and I was just wanting to know how many of you really think that the Resonator is the main cause of the "rattling" noise that so many SVX's make? I really need to get rid of this, although i'm sure that THIS problem will have to wait until I get rich and can fix the other problem I'm having. Let me know.


Thanks, Allen

Allen,

On my car, I have changed gaskets, I have tried to find fault (as in noise) coming form the heat shield. Yes heatshield does make some noise but majority of them come form the resonator. Most shops refuse to take the resonator out (thinking it's another cat. SVX has 3 cats total. one on each side of before the "Y" and one right after the "Y". Then resonator. If they do take the resonator out and straight pipe it for you, the cost will depend on the shop that did the job. Mine took 30 bucks away.

Good luck

Lwin

[wasions]

There are lots of places that srones can hide under the car. When they get there, they rattle. Just to be sure, next time the car's on a rack (as it should be soon, according to your spring/shock post), take a little metal hammer and start tapping on things. You'll find the problem.

Steve

After posting more then once on this subject and talking to several mech I decided to just have my resonator removed for 30 bucks by the local shop. Not only is the ratlle gone but it has a nicer tone as well. Well good luck with your fixes.

Later
Chris

[dromano]

Wife's car had a rattle, knew it was a cat. Finally replaced the resonator, rattle gone!!!

Alright, thanks everyone. Seeing as I've already had the heat shield repaired, I think I'll ask around about having the resonator taken out and replacing it with a straight pipe. I'm not really good at Mechanical stuff, and I was just wondering what exactly the Resonator does? I know it's probably not important, otherwise you all wouldn't tell me to get rid of it but I'm just curious as to what it's purpose is. Thanks Again Everyone.



Allen

[wasions]

Uhhh. I think it, like, tends to resonate and stuff.

Glad to be of service.

Steve

[Seraph]

Originally posted by SVXtremist
Alright, thanks everyone. Seeing as I've already had the heat shield repaired, I think I'll ask around about having the resonator taken out and replacing it with a straight pipe. I'm not really good at Mechanical stuff, and I was just wondering what exactly the Resonator does? I know it's probably not important, otherwise you all wouldn't tell me to get rid of it but I'm just curious as to what it's purpose is. Thanks Again Everyone.



Allen

Chances are I am wrong but this is what I saw... It is a straight pipe made out of a mash so that the muffler section of the pipe and the rest of the pipe can bend and slightly give a bit under stress and lots of movement. I think that's its job. And over the years, the resonator's mashed interior would break down and start to rattle. Chances are I am wrong but I think that's what the resonator does on the SVX

Lwin

[immortal_suby]

There was a good post here a while back on what a resonator does and I will try to summarize it in simple terms. At lower RPM's your exhaust "waves" flow differently and in order to make more torque at the low RPM's the waves need a place to expand sooner than the length of your whole exhaust system. The resonator allows this by creating a place for the exhaust to expand without traveling to the end of the tailpipe.
So theoretically, if you were to hook an svx up to a dyno with a "properly functioning" resonator and test it against one with a straight pipe, the one with the resonator would generate more torque at lower RPM's.
Whether the burned out resonators that are in most of our high mileage svx's are helping or hindering is a question only a dyno could answer. I took mine off, looked inside and saw basically a straight through pipe with holes drilled in it. I shook it as hard as I could and nothing rattled inside. I was going to cut it open with a saw one day and take pictures of the innards but I threw it out instead. I put in a straight pipe and then later put in a glasspack only because it was too loud with the straight pipe (I do not have a stock exhaust system) I saw no seat of the pants power difference between the two.

[oab_au]

Hi Sube,
Pretty close.
I posted this on Yahoo, I think, but I'll put it up here.

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 about 50 to 60degs before bottom dead centre on the end of the power stroke (I don't know the SVX timings) 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 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.
I did warn that it was a bit technical. Phew!
all the best Harvey.

[Ron Mummert]

Originally posted by oab_au
Hi Sube,
Pretty close.
I posted this on Yahoo, I think, but I'll put it up here.

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 about 50 to 60degs before bottom dead centre on the end of the power stroke (I don't know the SVX timings) 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 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.
I did warn that it was a bit technical. Phew!
all the best Harvey.

Um... Phew & double phew. So, Harvey, to those of us who ripped off that rattlin' bad boy & replaced it with straight metal; what obvious effect should we notice? I can't tell any difference, but I don't do any acrobatics at the race track either. If I've lost 5 mph of top speed, it's worth getting rid of the public smirks in the shopping center parking lot when at 10 mph, the car sounded like a rattlesnake.
But, thanks anyway, I think. Ron.

[oab_au]

Hi Ron
The effect, besides the peace and quite, would a tapering off, of the torque curve after about 5500. 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, (I think this is what Cdigerlando was experiencing when he had the turbo on, an unaccounted rise in boost pressure at the top end).
Not having the resonator in place means that the exhaust pressure plug has to travel down to the 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.
Sorry this is so involved but it's probably why it's function is so misunderstood
Harvey.

[immortal_suby]

dang, I knew I was gonna foul that one up. I thought that you posted that here but I couldn't find it. Thanks for the lesson again.