muffler/exhaust change =HP loss

[3Twenty8xi]

I recently changed my muffler and exhaust pipe on my 2007 328xi. I got the sound I was looking for..not too loud, but i noticed a decrease in performance . I feel a loss of power when accelerating..Im thinking maybe the size of the pipe I added has to do with the problem. Any suggestions on size or input on what would be best to do? Thanks in advance. :help

[AZG1164]

....changed them to what? More info needed.

[mattjw916]

the seat-of-the-pants dyno is rarely correct...

[Takashi]

I recently changed my muffler and exhaust pipe on my 2007 328xi. I got the sound I was looking for..not too loud, but i noticed a decrease in performance . I feel a loss of power when accelerating..Im thinking maybe the size of the pipe I added has to do with the problem. Any suggestions on size or input on what would be best to do? Thanks in advance. :help

If the exhaust is louder to the stock exhaust, you have lost some energy to sound.

[mattjw916]

man, those F1 cars must not make any power at all then since they are so loud...

/facepalm

[AZG1164]

If the exhaust is louder to the stock exhaust, you have lost some energy to sound.


man, those F1 cars must not make any power at all then since they are so loud...
/facepalm

Winner.

[3Twenty8xi]

Not enough backpressure = low end torque I think

[Razor2010]

If the exhaust is louder to the stock exhaust, you have lost some energy to sound.


ROFL :lol:lol:lol:lol:lol:lol:lol:lol:lol:lol:lol:lol:l ol:lol

[Takashi]

man, those F1 cars must not make any power at all then since they are so loud...

/facepalm

It sounds funny but if you think more indepth, energy generated in an engine is either transferred to do work, transferred to heat, or sound. Race car engines are noisy but they are fitted with bigger engines thus the energy loss is compensated.

[mattjw916]

I'm not an automotive engineer but I'm willing to bet that is not a significant factor relatively speaking.

As I understand it (again, I'm not an expert) the reason why internal combustion engines are so loud is that the wavefront of the flame-wave as combustion occurs is exceeding the speed of sound, hence a "crack". Multiply that many thousands of times based on the engine speed and you have some serious noise.

To combat this most cars have baffles in the muffler which make the exhaust gases snake their way through canceling the pulses out (crappy explanation but you get the idea). High performance mufflers will often have no baffles at all such as in glass packs where the gas passes through a perforated mesh and sound deadening material (common on performance motorcycle exhausts like my Ducati for instance). Really good performance mufflers (powerful and quiet) will have limited baffles and sound deadening material so you get the high flow for top-end power but don't attract the attention of johnny-law in the process.

[floydr]

It sounds funny but if you think more indepth, energy generated in an engine is either transferred to do work, transferred to heat, or sound. Race car engines are noisy but they are fitted with bigger engines thus the energy loss is compensated.

F1 engines are 2.4L; kind of puts a crimp on your "bigger" argument.

Race car engines are loud because THEY DON'T HAVE A MUFFLER. Look, you're ignoring heat. As the exhaust gas pressure waves bounce around in the muffler/exhaust system and get mixed, they end up mostly cancelling each other and transfer their sonic energy to heat. Think about the 2nd law of thermodynamics.

The fewer baffles, the less gas mixing, the more sound exits the exhaust pipes.

[GuyEsberg]

If the exhaust is louder to the stock exhaust, you have lost some energy to sound.
Nice logic on a faulty premise. There is not a direct correlation between power and sound, at least in real-world terms; there are too many other variables that come into play. I've never run across increasing engine size (or output for that matter) to compensate for increases in engine or exhaust noise, whether in internal combustion or other motive power sources. As others have replied, the issue is most likely due to non-optimized back pressure.

[Georgere]

from my sportbike experience, when you change exhaust you need to remap fuel map and open up air input (i.e. install thinner air filter that would let more air in) and this is at the very least. the right job is all of the above plus bigger headers plus more (forgot the name of other parts).
by changing exhaust only you definitely loose somewhere in the power-band