Exhaust welding and cat delete
07-12-2011, 03:28 PM
#13
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It really depends on 2 things:
1) Change in the physical dimensions of the cat (specifically, length and diameter) and
2) What kind of baffling you have mounted downstream from the cats.
On our 12-valves, there are 2 mufflers mounted (in sequence) after the 2 cats are joined together by a "Y" pipe. The first muffler is actually the most important, since it is mounted directly under your ****. It absorbs most of the low-pitch rumble that causes buzz and shakes. The second muffler, at the rear bumper, quiets the high-pitched "ricey" tin-can echo effect that all small-displacement engines produce.
Andy, your success in changing the tone of your exhaust note is likely due to the fact that a N/A 944 only has one muffler mounted after the cats are joined. If you change (enlarge) the inner diameter of the cat body, you will "megaphone" the exhaust sound coming through the cat, and you will definitely hear (and also feel) an increase in the force of the sound vibrations travelling through the entire exhaust.
Grillage, if you do the REALLY smart thing and keep 2 mufflers mounted after the cats on your car, you might notice a slight change in sound coming out the tail pipe. But the change in sound will more likely be due to the fact that you have 2 properly functioning cats that are allowing your O2 sensors, EGR and MAF to function in harmony for the first time in probably a loooong time.
1) Change in the physical dimensions of the cat (specifically, length and diameter) and
2) What kind of baffling you have mounted downstream from the cats.
On our 12-valves, there are 2 mufflers mounted (in sequence) after the 2 cats are joined together by a "Y" pipe. The first muffler is actually the most important, since it is mounted directly under your ****. It absorbs most of the low-pitch rumble that causes buzz and shakes. The second muffler, at the rear bumper, quiets the high-pitched "ricey" tin-can echo effect that all small-displacement engines produce.
Andy, your success in changing the tone of your exhaust note is likely due to the fact that a N/A 944 only has one muffler mounted after the cats are joined. If you change (enlarge) the inner diameter of the cat body, you will "megaphone" the exhaust sound coming through the cat, and you will definitely hear (and also feel) an increase in the force of the sound vibrations travelling through the entire exhaust.
Grillage, if you do the REALLY smart thing and keep 2 mufflers mounted after the cats on your car, you might notice a slight change in sound coming out the tail pipe. But the change in sound will more likely be due to the fact that you have 2 properly functioning cats that are allowing your O2 sensors, EGR and MAF to function in harmony for the first time in probably a loooong time.
07-12-2011, 03:30 PM
#14
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Cats
What do you guys recomend replacing the cats with? I think mine also need to be replaced, but i obviously dont want to spend the money on a new cat from the dealership, and i also am leery about aftermarket cats because i dont want it to sound like ****. Any suggestions on an aftermarket cat that wont affect the exhaust tone/volume to significantly?
for just about 10 years.
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1995 Sport Audi 90 Quattro
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07-12-2011, 08:23 PM
#15
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It really depends on 2 things:
1) Change in the physical dimensions of the cat (specifically, length and diameter) and
2) What kind of baffling you have mounted downstream from the cats.
On our 12-valves, there are 2 mufflers mounted (in sequence) after the 2 cats are joined together by a "Y" pipe. The first muffler is actually the most important, since it is mounted directly under your ****. It absorbs most of the low-pitch rumble that causes buzz and shakes. The second muffler, at the rear bumper, quiets the high-pitched "ricey" tin-can echo effect that all small-displacement engines produce.
Andy, your success in changing the tone of your exhaust note is likely due to the fact that a N/A 944 only has one muffler mounted after the cats are joined. If you change (enlarge) the inner diameter of the cat body, you will "megaphone" the exhaust sound coming through the cat, and you will definitely hear (and also feel) an increase in the force of the sound vibrations travelling through the entire exhaust.
Grillage, if you do the REALLY smart thing and keep 2 mufflers mounted after the cats on your car, you might notice a slight change in sound coming out the tail pipe. But the change in sound will more likely be due to the fact that you have 2 properly functioning cats that are allowing your O2 sensors, EGR and MAF to function in harmony for the first time in probably a loooong time.
1) Change in the physical dimensions of the cat (specifically, length and diameter) and
2) What kind of baffling you have mounted downstream from the cats.
On our 12-valves, there are 2 mufflers mounted (in sequence) after the 2 cats are joined together by a "Y" pipe. The first muffler is actually the most important, since it is mounted directly under your ****. It absorbs most of the low-pitch rumble that causes buzz and shakes. The second muffler, at the rear bumper, quiets the high-pitched "ricey" tin-can echo effect that all small-displacement engines produce.
Andy, your success in changing the tone of your exhaust note is likely due to the fact that a N/A 944 only has one muffler mounted after the cats are joined. If you change (enlarge) the inner diameter of the cat body, you will "megaphone" the exhaust sound coming through the cat, and you will definitely hear (and also feel) an increase in the force of the sound vibrations travelling through the entire exhaust.
Grillage, if you do the REALLY smart thing and keep 2 mufflers mounted after the cats on your car, you might notice a slight change in sound coming out the tail pipe. But the change in sound will more likely be due to the fact that you have 2 properly functioning cats that are allowing your O2 sensors, EGR and MAF to function in harmony for the first time in probably a loooong time.
07-14-2011, 05:44 AM
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[Andy1212]"Yes I am aware of how exhaust tone and volume is created, I was just wondering how much of an effect flow through universal cats had on these cars exhaust systems."
No, you're not wondering how much of an effect flow has. Not by asking the question to which I responded: "Really? I used magnaflow cats on my porsche 944, and it made a huge difference in both tone and volume. Can anyone else confirm this?"
I gave you a solid, educated and direct answer to your question, and now you're telling me that's not what you were asking?
OK, let me try this again... but for your second question. Flow alone will not change tone. It will, however, change the efficiency and resultant "smooth" tone of your engine's combustion. But any change of sound created by switching cats is PURELY due to changes in the stoichiometric requirements of the engine. Different models of cats will throw different ratios of exhaust contents at your O2 sensors, which will tell your fuel injection system to alter its mixture.
That's it. Cats don't baffle. At least, they are not intended to baffle. They are intended to allow the most free rate of flow possible, SPECIFICALLY because they play such an important part in how well/poorly engines run.
Tanking into consideration that a N/A 944 only has a set of cats mounted prior to its single muffler, it stands to reason that it's possible that Ferdinand's engineers designed some accoustic-dampening traits into the stock cats. That would save the solitary muffler from excess vibrational stress, and it would also explain the change in tone you experienced when you switched to magnaflow. I don't know. I'm just speculating.
No, you're not wondering how much of an effect flow has. Not by asking the question to which I responded: "Really? I used magnaflow cats on my porsche 944, and it made a huge difference in both tone and volume. Can anyone else confirm this?"
I gave you a solid, educated and direct answer to your question, and now you're telling me that's not what you were asking?
OK, let me try this again... but for your second question. Flow alone will not change tone. It will, however, change the efficiency and resultant "smooth" tone of your engine's combustion. But any change of sound created by switching cats is PURELY due to changes in the stoichiometric requirements of the engine. Different models of cats will throw different ratios of exhaust contents at your O2 sensors, which will tell your fuel injection system to alter its mixture.
That's it. Cats don't baffle. At least, they are not intended to baffle. They are intended to allow the most free rate of flow possible, SPECIFICALLY because they play such an important part in how well/poorly engines run.
Tanking into consideration that a N/A 944 only has a set of cats mounted prior to its single muffler, it stands to reason that it's possible that Ferdinand's engineers designed some accoustic-dampening traits into the stock cats. That would save the solitary muffler from excess vibrational stress, and it would also explain the change in tone you experienced when you switched to magnaflow. I don't know. I'm just speculating.
Last edited by Loudgoldwing; 07-14-2011 at 11:11 AM.
07-14-2011, 11:33 AM
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With the condition your current cats are in, any new aftermarket converters will quiet it down. If you still have the factory resonator and muffler, you really don't have much to worry about in the sound department.
07-14-2011, 10:53 PM
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[Andy1212]"Yes I am aware of how exhaust tone and volume is created, I was just wondering how much of an effect flow through universal cats had on these cars exhaust systems."
No, you're not wondering how much of an effect flow has. Not by asking the question to which I responded: "Really? I used magnaflow cats on my porsche 944, and it made a huge difference in both tone and volume. Can anyone else confirm this?"
I gave you a solid, educated and direct answer to your question, and now you're telling me that's not what you were asking?
OK, let me try this again... but for your second question. Flow alone will not change tone. It will, however, change the efficiency and resultant "smooth" tone of your engine's combustion. But any change of sound created by switching cats is PURELY due to changes in the stoichiometric requirements of the engine. Different models of cats will throw different ratios of exhaust contents at your O2 sensors, which will tell your fuel injection system to alter its mixture.
That's it. Cats don't baffle. At least, they are not intended to baffle. They are intended to allow the most free rate of flow possible, SPECIFICALLY because they play such an important part in how well/poorly engines run.
Tanking into consideration that a N/A 944 only has a set of cats mounted prior to its single muffler, it stands to reason that it's possible that Ferdinand's engineers designed some accoustic-dampening traits into the stock cats. That would save the solitary muffler from excess vibrational stress, and it would also explain the change in tone you experienced when you switched to magnaflow. I don't know. I'm just speculating.
No, you're not wondering how much of an effect flow has. Not by asking the question to which I responded: "Really? I used magnaflow cats on my porsche 944, and it made a huge difference in both tone and volume. Can anyone else confirm this?"
I gave you a solid, educated and direct answer to your question, and now you're telling me that's not what you were asking?
OK, let me try this again... but for your second question. Flow alone will not change tone. It will, however, change the efficiency and resultant "smooth" tone of your engine's combustion. But any change of sound created by switching cats is PURELY due to changes in the stoichiometric requirements of the engine. Different models of cats will throw different ratios of exhaust contents at your O2 sensors, which will tell your fuel injection system to alter its mixture.
That's it. Cats don't baffle. At least, they are not intended to baffle. They are intended to allow the most free rate of flow possible, SPECIFICALLY because they play such an important part in how well/poorly engines run.
Tanking into consideration that a N/A 944 only has a set of cats mounted prior to its single muffler, it stands to reason that it's possible that Ferdinand's engineers designed some accoustic-dampening traits into the stock cats. That would save the solitary muffler from excess vibrational stress, and it would also explain the change in tone you experienced when you switched to magnaflow. I don't know. I'm just speculating.
And it is well known that factory cats are not designed to be "They are intended to allow the most free rate of flow possible, SPECIFICALLY because they play such an important part in how well/poorly engines run." The flow restriction of the cats is taken into consideration when designing exhaust systems with the backpressure requirements. I dont know where you are getting this information, but it is quite inaccurate..
But I digress, this is beside the point.
Last edited by Andy1212; 07-14-2011 at 10:58 PM.
08-13-2016, 02:29 PM
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So I am very much a newcomer to all things car modding but i got a question and will get to the point. Ive just recently got myself a 1995 audi 90 Q and am pretty sure one or both of my cats needs replacing and i would love to either fit some straight pipes or high flow cats with maybe some quality mufflers who knows? but I cant find for the life of me find any aftermarket exhaust systems or for that matter pretty much anything for the 90 and up until these forums found vary little about people modding audi 80 and 90. So my question is what have you guys used on your car as far as exhuast systems and what do you suggest? Any help much appreciated
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