Gi Guys,
Here is some information with respect to the BMW exhaust, air flow, back pressure and it's design which was written by Steve Dinan. After reading this, I concluded that our car's resonator "more than likely" hurts the car when it comes down to horse power and overall performance. Here is S.D's information on this subject. What's your take on this matter? Based on his research, we should ditch our car's resonator, right ???
Thanks for your replies and sharing your opinion.
START >>>
Exhaust Theory
There are two major areas of the complete exhaust system that are typically tuned for enhanced performance; the exhaust manifold .or header and the rear muffler(s). The exhaust manifold’s length, tubing diameter and the manner in which each cylinder is linked to the other is critical when attempting to maximize an engine’s power output. The manifold configuration can be manipulated in order to generate maximum power at low, middle or high rpm, changing the shape of the power curve accordingly. Naturally some compromise must be accepted when tuning an exhaust manifold for a street-car as the goal is typically to ensure balanced power output at low, middle and high rpm. This is in contrast to a race-engine where the exhaust manifold can be tuned specifically for maximum performance at high rpm.
After the exhaust manifold or header, optimum performance comes from making the balance of the exhaust system as short and large as possible. This approach will result in greater engine efficiency for maximum power, as well as minimizing the weight of the system. Probably the best example of an optimized, no-compromise exhaust system would be that of an F1 racecar. If you have ever had the opportunity to hear an F1 exhaust note, I think you will agree that it is best described as deafening. Clearly an exhaust system that even approached such a volume level in a performance street-car would draw far too much of the wrong sort of attention. Therefore, a modern street-car exhaust represents a number of performance compromises in order to achieve an acceptable exhaust volume, as well as meeting emissions standards.
In order to accommodate the various components and baffling necessary for a street-car, the exhaust system becomes longer and the flow of gasses more circuitous as noise and emissions standards are addressed. Each bend in the exhaust tubing, catalytic converter, resonator and so forth introduces restrictions to the exhaust flow, particularly at higher rpm where flow is most critical. Exhaust flow can actually reach hundreds of miles per hour when the engine is producing maximum power, which results in power robbing friction along the exhaust tubing
walls, particularly when the gasses must change direction. This friction results in increased backpressure that can be quantified with a pressure gauge. In addition to the friction issue, a tube or opening that is too small will result in extra backpressure as well. This backpressure restricts the amount of gasses that can be passed through the engine, resulting in a reduction of peak power.
I’m fairly certain that many of you have been exposed to a “bench racing legend” that would have you believe that increased backpressure will improve low rpm power and that low backpressure will increase high rpm output. Nothing could be further from the truth. An exhaust system is sized for maximum flow at wide-open-throttle and peak rpm. All exhaust systems are “oversized” for lower engine speeds (rpm), as backpressure is so insignificant that it can’t even be measured. Less back-pressure always results in more power at higher rpm, with no negative effect on lower engine speed performance. The amount of power that can be extracted from an
engine at a given rpm as a result of exhaust design is really limited by the exhaust manifold or header. After the header, less backpressure is always better.
The real challenge when tuning a street-car exhaust is to increase flow without making the system so loud as it becomes unacceptable or even illegal. It is also important to understand that vehicle manufacturers must meet more stringent maximum volume requirements than aftermarket manufacturers.
BMW’s current M-cars feature a distinctive quad exhaust tip design, punctuating the cars’ high performance image. This approach is very logical when applied to a “V” engine configuration because there are natural dual exhaust outputs with this engine design. >>> END.
-------------------------------------------------------------------------- :cheers:
Here is some information with respect to the BMW exhaust, air flow, back pressure and it's design which was written by Steve Dinan. After reading this, I concluded that our car's resonator "more than likely" hurts the car when it comes down to horse power and overall performance. Here is S.D's information on this subject. What's your take on this matter? Based on his research, we should ditch our car's resonator, right ???
Thanks for your replies and sharing your opinion.
START >>>
Exhaust Theory
There are two major areas of the complete exhaust system that are typically tuned for enhanced performance; the exhaust manifold .or header and the rear muffler(s). The exhaust manifold’s length, tubing diameter and the manner in which each cylinder is linked to the other is critical when attempting to maximize an engine’s power output. The manifold configuration can be manipulated in order to generate maximum power at low, middle or high rpm, changing the shape of the power curve accordingly. Naturally some compromise must be accepted when tuning an exhaust manifold for a street-car as the goal is typically to ensure balanced power output at low, middle and high rpm. This is in contrast to a race-engine where the exhaust manifold can be tuned specifically for maximum performance at high rpm.
After the exhaust manifold or header, optimum performance comes from making the balance of the exhaust system as short and large as possible. This approach will result in greater engine efficiency for maximum power, as well as minimizing the weight of the system. Probably the best example of an optimized, no-compromise exhaust system would be that of an F1 racecar. If you have ever had the opportunity to hear an F1 exhaust note, I think you will agree that it is best described as deafening. Clearly an exhaust system that even approached such a volume level in a performance street-car would draw far too much of the wrong sort of attention. Therefore, a modern street-car exhaust represents a number of performance compromises in order to achieve an acceptable exhaust volume, as well as meeting emissions standards.
In order to accommodate the various components and baffling necessary for a street-car, the exhaust system becomes longer and the flow of gasses more circuitous as noise and emissions standards are addressed. Each bend in the exhaust tubing, catalytic converter, resonator and so forth introduces restrictions to the exhaust flow, particularly at higher rpm where flow is most critical. Exhaust flow can actually reach hundreds of miles per hour when the engine is producing maximum power, which results in power robbing friction along the exhaust tubing
walls, particularly when the gasses must change direction. This friction results in increased backpressure that can be quantified with a pressure gauge. In addition to the friction issue, a tube or opening that is too small will result in extra backpressure as well. This backpressure restricts the amount of gasses that can be passed through the engine, resulting in a reduction of peak power.
I’m fairly certain that many of you have been exposed to a “bench racing legend” that would have you believe that increased backpressure will improve low rpm power and that low backpressure will increase high rpm output. Nothing could be further from the truth. An exhaust system is sized for maximum flow at wide-open-throttle and peak rpm. All exhaust systems are “oversized” for lower engine speeds (rpm), as backpressure is so insignificant that it can’t even be measured. Less back-pressure always results in more power at higher rpm, with no negative effect on lower engine speed performance. The amount of power that can be extracted from an
engine at a given rpm as a result of exhaust design is really limited by the exhaust manifold or header. After the header, less backpressure is always better.
The real challenge when tuning a street-car exhaust is to increase flow without making the system so loud as it becomes unacceptable or even illegal. It is also important to understand that vehicle manufacturers must meet more stringent maximum volume requirements than aftermarket manufacturers.
BMW’s current M-cars feature a distinctive quad exhaust tip design, punctuating the cars’ high performance image. This approach is very logical when applied to a “V” engine configuration because there are natural dual exhaust outputs with this engine design. >>> END.
-------------------------------------------------------------------------- :cheers: