550i Muffler Delete questions - pls help
05-07-2014, 04:45 PM
#1
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550i Muffler Delete questions - pls help
Hi I'm looking to do an inexpensive exhaust mod.
I've searched the forum and have watched the vids so I'm sure this is what I want to do based on the $$. I want to keep the single sided outlet exhaust. I found a great deal on exhaust tips today with 3" inlet and 3.5" dual tips on ebay. I went to the muffler shop today and put the car on the lift and I have the following questions
1. Should I use a 3" straight pipe or a 2.5" straight pipe. It looks like either will work but which is better?
2. Should I cut the OEM exhaust and muffler right behind the rear axle or closer to the OEM resonator?
3. Will the exhaust tips I purchased today with the 3" inlet work with both 3" and/or 2.5" diameter straight pipe options? If I need to get an exhaust tip with 2.5" inlet then I will.
Thanks for the help.
I've searched the forum and have watched the vids so I'm sure this is what I want to do based on the $$. I want to keep the single sided outlet exhaust. I found a great deal on exhaust tips today with 3" inlet and 3.5" dual tips on ebay. I went to the muffler shop today and put the car on the lift and I have the following questions
1. Should I use a 3" straight pipe or a 2.5" straight pipe. It looks like either will work but which is better?
2. Should I cut the OEM exhaust and muffler right behind the rear axle or closer to the OEM resonator?
3. Will the exhaust tips I purchased today with the 3" inlet work with both 3" and/or 2.5" diameter straight pipe options? If I need to get an exhaust tip with 2.5" inlet then I will.
Thanks for the help.
05-07-2014, 05:32 PM
#2
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1) You should match the cross-sectional area of the existing pipe. Be careful though, the pipe is not cylindrical, so your A = Pi*r(2) formula won't directly apply here.
2) Up to you.
3) Probably.
I must say, it really seems like a bad idea choking down the nearly 4" diameter rear section to a 2.5" or 3" pipe.
2) Up to you.
3) Probably.
I must say, it really seems like a bad idea choking down the nearly 4" diameter rear section to a 2.5" or 3" pipe.
05-08-2014, 12:45 AM
#3
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1) You should match the cross-sectional area of the existing pipe. Be careful though, the pipe is not cylindrical, so your A = Pi*r(2) formula won't directly apply here.
2) Up to you.
3) Probably.
I must say, it really seems like a bad idea choking down the nearly 4" diameter rear section to a 2.5" or 3" pipe.
2) Up to you.
3) Probably.
I must say, it really seems like a bad idea choking down the nearly 4" diameter rear section to a 2.5" or 3" pipe.
Thanks for the reply. Wouldn't I still be reducing the pipe size if I down a cat back or a muffler delete because the inlet on the cat back is less than the OEM pipe as well?
I don't want to loss power but I hear and see good results on sound with a muffler delete without losing power or spending a grand. I just need the specs from someone with a 550 that's done it successfully.
05-08-2014, 02:32 AM
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One thing you should consider is that when you delete the muffler, you are reducing back pressure and when you increase the pipe you're doing the same. I've heard that back pressure loss can cause a reduction in hp. Also, you will need a good set of earplugs for you and you passengers because the drone is going to be crazy...
05-08-2014, 08:45 AM
#5
Senior Members
As a general rule, if you pull a muffler out, replace it with piping that uses the same cross-sectional area.
05-08-2014, 08:48 AM
#6
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One thing you should consider is that when you delete the muffler, you are reducing back pressure and when you increase the pipe you're doing the same. I've heard that back pressure loss can cause a reduction in hp. Also, you will need a good set of earplugs for you and you passengers because the drone is going to be crazy...
"
Destroying a myth.
Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.
"
05-08-2014, 11:31 AM
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(from: UUC MOTORWERKS)
"
Destroying a myth.
Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.
"
"
Destroying a myth.
Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.
"
It's the same stuff I've been telling people for years but nobody seems to get it.
Think about it.....if backpressure equaled horsepower, there would be huge restrictive mufflers on top fuel dragsters and other high-end race cars.
It's amazing how quickly misinformation can can be spread, and believed by unsuspecting people on these forums.
Last edited by 1970Gizmo; 05-08-2014 at 11:33 AM.
05-08-2014, 12:25 PM
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maybe this helps with your decision. As far as the sound, I love it but if you're like me, my fiancee doesn't like it but it's MY CAR, haha. Having the parents in the car might be too loud as well. Just FYI. It was $60 install, straight pipe. Planning on getting a muffler to replace the straight pipe.
this is the exhaust tip I got,
stock:
installed:
this is the exhaust tip I got,
stock:
installed:
Last edited by wises; 05-08-2014 at 12:37 PM.
05-08-2014, 01:55 PM
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[QUOTE=west;1538503](from: UUC MOTORWERKS)
"
Destroying a myth.
Some say that "an engine needs backpressure to work correctly." Is this true?
Yeah, luckily I said i "heard" that it can cause a loss... I've actually read several post here where members went to quads and felt a loss. When I added quads to my 535 I did not feel a loss until I added a second turbo muff to kill the drone. From the original quad setup to what I have now the car for a few hours felt a little less responsive. I don't notice it now.
"
Destroying a myth.
Some say that "an engine needs backpressure to work correctly." Is this true?
Yeah, luckily I said i "heard" that it can cause a loss... I've actually read several post here where members went to quads and felt a loss. When I added quads to my 535 I did not feel a loss until I added a second turbo muff to kill the drone. From the original quad setup to what I have now the car for a few hours felt a little less responsive. I don't notice it now.