Gundo Hack today (with removal and re-install)
#32
09-08-2011, 02:10 PM
Gundo is the best sounding muffler awe cats
Gundo is the best sounding muffler out there, at any price. For the ultimate, mate that with AWE 200 cell sport cats.
I am thinking of adding awe CATs with gundo hack. How much louder will it be? Any increase in horse power?
I am thinking of adding awe CATs with gundo hack. How much louder will it be? Any increase in horse power?
#33
09-08-2011, 02:48 PM
DoninDEN
I spent a good part of my career working on automotive exhaust systems with the major auto producers and the OEM plants producing those systems. There aren't any pure stainless steels for automotive exhaust systems. They fall into two major catagorys, austenitic and ferritic with titanium on some specialty cars. An aluminized carbon system would be lucky to see three years in the rust belt. For cars not driven in the snow and that were driven long enough to get up to operating temperature they might last longer.
The main failure modes of aluminized carbon steel in exhaust systems are condensate trapped between the inner and outer wrap resulting in a general corrosion and eventual perforation, hole, in the muffler which is usually on the bottom due to the ponding of the condensate. The other mode is along the weld seam of the tubing. The free aluminum coating on the surface sacrifices itself to protect the weld seam. At some point this stops due to the distance from the weld seam. At that point the galvanic protection flips and the iron in the base metal tries to protect the iron/aluminum alloy layer which is between the free aluminum and the base metal. That is what causes the long straight red line observed on aluminized carbon tubing in automotive exhaust systems. It's as if the weld unzipped itself.
Another really quick way to get a failure is to weld a piece of austenitic, 300 series, to an aluminized carbon steel. The same galvanic process occurs but it is a stronger couple and it doesn't flip. We used to see lots of older VWs with the tailpipe stub missing. Those stubs were 304 and the muffler was made from aluminized carbon steel. They sawed themselves off the muffler. I won't touch on the weld wire issue.
The average muffler shop just doesn't understand what happens when you weld two different materials together. There's a reason the factories don't mix materials.
Mike said they could do stainless for $50 more. I asked about the stainless vs. the aluminized steel and he said that the stainless in exhaust systems is not pure stainless and it can rust over time. He said on normal long exhaust systems they expect the aluminized stainless to last 8 to 10 years. The rusting starts from the inside and that it is more of an issue for cars that sit for a long period of time.
The main failure modes of aluminized carbon steel in exhaust systems are condensate trapped between the inner and outer wrap resulting in a general corrosion and eventual perforation, hole, in the muffler which is usually on the bottom due to the ponding of the condensate. The other mode is along the weld seam of the tubing. The free aluminum coating on the surface sacrifices itself to protect the weld seam. At some point this stops due to the distance from the weld seam. At that point the galvanic protection flips and the iron in the base metal tries to protect the iron/aluminum alloy layer which is between the free aluminum and the base metal. That is what causes the long straight red line observed on aluminized carbon tubing in automotive exhaust systems. It's as if the weld unzipped itself.
Another really quick way to get a failure is to weld a piece of austenitic, 300 series, to an aluminized carbon steel. The same galvanic process occurs but it is a stronger couple and it doesn't flip. We used to see lots of older VWs with the tailpipe stub missing. Those stubs were 304 and the muffler was made from aluminized carbon steel. They sawed themselves off the muffler. I won't touch on the weld wire issue.
The average muffler shop just doesn't understand what happens when you weld two different materials together. There's a reason the factories don't mix materials.
Last edited by Alan C.; 09-08-2011 at 02:50 PM.
#34
09-08-2011, 02:56 PM
Oh Snap!
That fabspeed is looking better.
That fabspeed is looking better.
DoninDEN
I spent a good part of my career working on automotive exhaust systems with the major auto producers and the OEM plants producing those systems. There aren't any pure stainless steels for automotive exhaust systems. They fall into two major catagorys, austenitic and ferritic with titanium on some specialty cars. An aluminized carbon system would be lucky to see three years in the rust belt. For cars not driven in the snow and that were driven long enough to get up to operating temperature they might last longer.
The main failure modes of aluminized carbon steel in exhaust systems are condensate trapped between the inner and outer wrap resulting in a general corrosion and eventual perforation, hole, in the muffler which is usually on the bottom due to the ponding of the condensate. The other mode is along the weld seam of the tubing. The free aluminum coating on the surface sacrifices itself to protect the weld seam. At some point this stops due to the distance from the weld seam. At that point the galvanic protection flips and the iron in the base metal tries to protect the iron/aluminum alloy layer which is between the free aluminum and the base metal. That is what causes the long straight red line observed on aluminized carbon tubing in automotive exhaust systems. It's as if the weld unzipped itself.
Another really quick way to get a failure is to weld a piece of austenitic, 300 series, to an aluminized carbon steel. The same galvanic process occurs but it is a stronger couple and it doesn't flip. We used to see lots of older VWs with the tailpipe stub missing. Those stubs were 304 and the muffler was made from aluminized carbon steel. They sawed themselves off the muffler. I won't touch on the weld wire issue.
The average muffler shop just doesn't understand what happens when you weld two different materials together. There's a reason the factories don't mix materials.
I spent a good part of my career working on automotive exhaust systems with the major auto producers and the OEM plants producing those systems. There aren't any pure stainless steels for automotive exhaust systems. They fall into two major catagorys, austenitic and ferritic with titanium on some specialty cars. An aluminized carbon system would be lucky to see three years in the rust belt. For cars not driven in the snow and that were driven long enough to get up to operating temperature they might last longer.
The main failure modes of aluminized carbon steel in exhaust systems are condensate trapped between the inner and outer wrap resulting in a general corrosion and eventual perforation, hole, in the muffler which is usually on the bottom due to the ponding of the condensate. The other mode is along the weld seam of the tubing. The free aluminum coating on the surface sacrifices itself to protect the weld seam. At some point this stops due to the distance from the weld seam. At that point the galvanic protection flips and the iron in the base metal tries to protect the iron/aluminum alloy layer which is between the free aluminum and the base metal. That is what causes the long straight red line observed on aluminized carbon tubing in automotive exhaust systems. It's as if the weld unzipped itself.
Another really quick way to get a failure is to weld a piece of austenitic, 300 series, to an aluminized carbon steel. The same galvanic process occurs but it is a stronger couple and it doesn't flip. We used to see lots of older VWs with the tailpipe stub missing. Those stubs were 304 and the muffler was made from aluminized carbon steel. They sawed themselves off the muffler. I won't touch on the weld wire issue.
The average muffler shop just doesn't understand what happens when you weld two different materials together. There's a reason the factories don't mix materials.
#35
09-08-2011, 05:12 PM
Apologies for appearing dense, but is the upshot of your statement that:
(1) doing this hack at all is bad?
(2) doing this hack is bad with stainless steel?
(3) doing this hack with the material that the OP used?
Thanks.
(1) doing this hack at all is bad?
(2) doing this hack is bad with stainless steel?
(3) doing this hack with the material that the OP used?
Thanks.
DoninDEN
I spent a good part of my career working on automotive exhaust systems with the major auto producers and the OEM plants producing those systems. There aren't any pure stainless steels for automotive exhaust systems. They fall into two major catagorys, austenitic and ferritic with titanium on some specialty cars. An aluminized carbon system would be lucky to see three years in the rust belt. For cars not driven in the snow and that were driven long enough to get up to operating temperature they might last longer.
The main failure modes of aluminized carbon steel in exhaust systems are condensate trapped between the inner and outer wrap resulting in a general corrosion and eventual perforation, hole, in the muffler which is usually on the bottom due to the ponding of the condensate. The other mode is along the weld seam of the tubing. The free aluminum coating on the surface sacrifices itself to protect the weld seam. At some point this stops due to the distance from the weld seam. At that point the galvanic protection flips and the iron in the base metal tries to protect the iron/aluminum alloy layer which is between the free aluminum and the base metal. That is what causes the long straight red line observed on aluminized carbon tubing in automotive exhaust systems. It's as if the weld unzipped itself.
Another really quick way to get a failure is to weld a piece of austenitic, 300 series, to an aluminized carbon steel. The same galvanic process occurs but it is a stronger couple and it doesn't flip. We used to see lots of older VWs with the tailpipe stub missing. Those stubs were 304 and the muffler was made from aluminized carbon steel. They sawed themselves off the muffler. I won't touch on the weld wire issue.
The average muffler shop just doesn't understand what happens when you weld two different materials together. There's a reason the factories don't mix materials.
I spent a good part of my career working on automotive exhaust systems with the major auto producers and the OEM plants producing those systems. There aren't any pure stainless steels for automotive exhaust systems. They fall into two major catagorys, austenitic and ferritic with titanium on some specialty cars. An aluminized carbon system would be lucky to see three years in the rust belt. For cars not driven in the snow and that were driven long enough to get up to operating temperature they might last longer.
The main failure modes of aluminized carbon steel in exhaust systems are condensate trapped between the inner and outer wrap resulting in a general corrosion and eventual perforation, hole, in the muffler which is usually on the bottom due to the ponding of the condensate. The other mode is along the weld seam of the tubing. The free aluminum coating on the surface sacrifices itself to protect the weld seam. At some point this stops due to the distance from the weld seam. At that point the galvanic protection flips and the iron in the base metal tries to protect the iron/aluminum alloy layer which is between the free aluminum and the base metal. That is what causes the long straight red line observed on aluminized carbon tubing in automotive exhaust systems. It's as if the weld unzipped itself.
Another really quick way to get a failure is to weld a piece of austenitic, 300 series, to an aluminized carbon steel. The same galvanic process occurs but it is a stronger couple and it doesn't flip. We used to see lots of older VWs with the tailpipe stub missing. Those stubs were 304 and the muffler was made from aluminized carbon steel. They sawed themselves off the muffler. I won't touch on the weld wire issue.
The average muffler shop just doesn't understand what happens when you weld two different materials together. There's a reason the factories don't mix materials.
#36
09-08-2011, 05:32 PM
Join Date: Jul 2011
Location: Denver, CO
Posts: 1,117
Rep Power: 77 
1) Doing the Gundo is great! If a louder and more aggressive sound is what you want. I love it.
2) Using stainless is the best way to do it. I didn't do it, because I wasn't smart enough to ask.
3) I have no problem with the aluminized steel, as given the heat generated by the engine and the angle of the bypass pipe, condensation should not be a problem and if it is, it is at least a decade from now. More likely 20 years before it is an issue with aluminized steel. But I would still pay the extra $50 for stainless if I were to redo it today.
Bottom line: Nothing at all bad about it. You have not heard one person go out of their way to post that they did not like it, instead numerous people have taken the time to post that they love it.
It is louder and more aggressive, maybe tone it down with a smaller diameter bypass pipe if you are concerned.
Where do you live? Maybe there is someone nearby that can let you hear it. Essentially as I understand it, it is the Porsche Sport Exhaust without a baffle to switch it off. The Gundo costs a couple hundred the PSE coats a couple thousand. Your choice if you want the switch.
2) Using stainless is the best way to do it. I didn't do it, because I wasn't smart enough to ask.
3) I have no problem with the aluminized steel, as given the heat generated by the engine and the angle of the bypass pipe, condensation should not be a problem and if it is, it is at least a decade from now. More likely 20 years before it is an issue with aluminized steel. But I would still pay the extra $50 for stainless if I were to redo it today.
Bottom line: Nothing at all bad about it. You have not heard one person go out of their way to post that they did not like it, instead numerous people have taken the time to post that they love it.
It is louder and more aggressive, maybe tone it down with a smaller diameter bypass pipe if you are concerned.
Where do you live? Maybe there is someone nearby that can let you hear it. Essentially as I understand it, it is the Porsche Sport Exhaust without a baffle to switch it off. The Gundo costs a couple hundred the PSE coats a couple thousand. Your choice if you want the switch.
Last edited by DoninDEN; 09-08-2011 at 05:42 PM.
#38
09-08-2011, 05:47 PM
Join Date: Jul 2011
Location: Denver, CO
Posts: 1,117
Rep Power: 77
Oh, OK, I thought you were asking me because I was being longwinded! The switch would be nice and if I ever decide to to that, I will gave only been out of pocket $225. Then I will be looking at a ton of options. Cattman's been around the Mod block and he loves it.
#39
09-08-2011, 06:20 PM
If you do the mod use 304L tubing and a 308L filler rod as your first choice. You could use 409 with the same filler but if you drive in the rain or worse salt the 409 will turn a nice rusty red. Aluminized low carbon steel is not a 10 year solution.
#42
09-08-2011, 07:48 PM
Enjoy your Gundo's, they look to be very well done, and I've seen many botch jobs out there.
CATTMAN
#43
09-08-2011, 08:28 PM
304L is a low carbon austenitic stainless. The low carbon is beneficial in welded exhaust systems.
There are lots of grades of stainless steel used in tubing. 409 and 304 are two of the most common grades for exhaust systems. 304 is the better of the two.
There are lots of grades of stainless steel used in tubing. 409 and 304 are two of the most common grades for exhaust systems. 304 is the better of the two.
#44
09-08-2011, 10:00 PM
Join Date: Jul 2011
Location: Denver, CO
Posts: 1,117
Rep Power: 77
Rich, you live in Colorado, the aluminized steel is a viable 10 year plus solution for a 4" bypass pipe.
Do you plan to drive your 911 in the winter? I don't, but in any event we us mag chloride here. so exterior rusting will not be an issue.
My winter car is a '98 Land Cruiser. It has an aluminized steel muffler and has never been garaged the 8 years I've owned it. It has the original exhaust system stretching 9 feet under the vehicle and has never had an exhaust issue.
So while I agree stainless would be best, don't over worry about it.
If you want to hear mine, let me know. I'm in the Bonnie Brae area and office downtown.
Don
Do you plan to drive your 911 in the winter? I don't, but in any event we us mag chloride here. so exterior rusting will not be an issue.
My winter car is a '98 Land Cruiser. It has an aluminized steel muffler and has never been garaged the 8 years I've owned it. It has the original exhaust system stretching 9 feet under the vehicle and has never had an exhaust issue.
So while I agree stainless would be best, don't over worry about it.
If you want to hear mine, let me know. I'm in the Bonnie Brae area and office downtown.
Don
#45
09-09-2011, 09:39 AM
Don, with a 98 there is a chance that your system is made from aluminized 409. You couldn't tell the difference looking. There are some 2000 Taurus models with Al-409 running around that still have the original system on them.
No OE today would put an aluminized carbon system on a car and they could save a substantial amount of money doing it but they won't due to system life.
The mod to the OP's muffler may make 10 years as we have seen the odd outlier in studies done in the past. Certainly leaving a car outside in the winter is a plus. We found exhaust systems in Sweden, few garages, lasted longer than their counter parts in the US. Water and salts remain frozen outside where they will thaw and become a liquid inside thus promoting corrosion.
My point to all of this is to get it done right. Be knowledgeable on the way in and tell the shop what you want. Done right it will last every bit as long as the original system on the car. Hopefully someone reading this and contemplating the modification will use this information.
No OE today would put an aluminized carbon system on a car and they could save a substantial amount of money doing it but they won't due to system life.
The mod to the OP's muffler may make 10 years as we have seen the odd outlier in studies done in the past. Certainly leaving a car outside in the winter is a plus. We found exhaust systems in Sweden, few garages, lasted longer than their counter parts in the US. Water and salts remain frozen outside where they will thaw and become a liquid inside thus promoting corrosion.
My point to all of this is to get it done right. Be knowledgeable on the way in and tell the shop what you want. Done right it will last every bit as long as the original system on the car. Hopefully someone reading this and contemplating the modification will use this information.