A surprising extra benefit of ACM exhaust

Ateam · 12-09-2011, 08:49 PM

I cannot speak to many of the other ones out there, but I am sure most of them are a "straight pipe" to some degree with varying amounts of absorption material and different size/shape hemoltz resonators however the ACM mod is 2 straight pipes basically through the hemoltz resonator. This is such a more direct path than the zig zaggin tight turns of the OEM exhaust. SO obviously its nice and loud and sounds good BUT

I actually picked up 2 mpg on the freeway-was able to hit 27mpg going 70mph on the same road I go on almost every day, same temps out, same gas etc. I have driven over 25 times with this car and always try to see how much economy I can get on the long stretch of 20 minutes on the freeway. Consistently 25 is the highest i hit and usually end up at 23-24. I never saw 26 even for a moment, let alone 27!

I would like to take a longer trip and watch the mileage. I only went about 10 miles and then a HUGE long tunnel was coming up and had to have some fun so dropped the mpg down to 16 quickly!

Anyway anyone else get better mpg with the exhaust? Since I assume that means much less back pressure and more engine efficiency, I am curious if there is some decent hp gains with this (decent I mean 4-6hp for a rear which is good!) I know MOST cars do not make much power with a rear only but the zig zag stock design really must do a number on exhaust velocity at the end of the muffler system and cause some degree of back pressure that is alleviated with 2 straight pipes.

Bart@AUTOcouture · 12-10-2011, 09:50 AM

Awesome observation. Glad you are enjoying it! I love mine

Ateam · 12-11-2011, 08:13 PM

Wow, thought more people would be pretty stoked to gain an extra 2mpg on the freeway if they were commuters!

I would assume this is "proof" that airflow is better and less restricted which also should have a good effect on power.

I would be curious if some of the other exhausts that do not use a straight pipe also help mpg

This exhaust sounds like a lambo (only at much lower volume) its awesome!

12-09-2011, 08:49 PM	#1
Ateam Banned 88 Rep 1,105 Posts Drives: M3 Join Date: Sep 2011 Location: USA iTrader: (0)	A surprising extra benefit of ACM exhaust I cannot speak to many of the other ones out there, but I am sure most of them are a "straight pipe" to some degree with varying amounts of absorption material and different size/shape hemoltz resonators however the ACM mod is 2 straight pipes basically through the hemoltz resonator. This is such a more direct path than the zig zaggin tight turns of the OEM exhaust. SO obviously its nice and loud and sounds good BUT I actually picked up 2 mpg on the freeway-was able to hit 27mpg going 70mph on the same road I go on almost every day, same temps out, same gas etc. I have driven over 25 times with this car and always try to see how much economy I can get on the long stretch of 20 minutes on the freeway. Consistently 25 is the highest i hit and usually end up at 23-24. I never saw 26 even for a moment, let alone 27! I would like to take a longer trip and watch the mileage. I only went about 10 miles and then a HUGE long tunnel was coming up and had to have some fun so dropped the mpg down to 16 quickly! Anyway anyone else get better mpg with the exhaust? Since I assume that means much less back pressure and more engine efficiency, I am curious if there is some decent hp gains with this (decent I mean 4-6hp for a rear which is good!) I know MOST cars do not make much power with a rear only but the zig zag stock design really must do a number on exhaust velocity at the end of the muffler system and cause some degree of back pressure that is alleviated with 2 straight pipes.
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12-10-2011, 09:50 AM	#2
Bart@AUTOcouture BimmerPost Supporting Vendor 1006 Rep 4,619 Posts Drives: F95X5M \| E46M3 \| E92M3 \| E60M5 Join Date: Feb 2006 Location: South Florida iTrader: (5)	Awesome observation. Glad you are enjoying it! I love mine
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12-11-2011, 08:13 PM	#3
Ateam Banned 88 Rep 1,105 Posts Drives: M3 Join Date: Sep 2011 Location: USA iTrader: (0)	Wow, thought more people would be pretty stoked to gain an extra 2mpg on the freeway if they were commuters! I would assume this is "proof" that airflow is better and less restricted which also should have a good effect on power. I would be curious if some of the other exhausts that do not use a straight pipe also help mpg This exhaust sounds like a lambo (only at much lower volume) its awesome!
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