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      11-12-2010, 02:39 PM   #1
ecksreturns
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Akrapovic GT4 Full catless exhaust review

Hi guys. I just got the Akra GT4 full catless exhaust installed on my m3 . Wow! What a huge difference it makes , especially in combination with the ESS S/c.

I had the ER installed originally and loved the bass it added to the exhaust note. Then I added the Fabspeed HFC and X pipe. The setup was good for some time but then I realized that it did not suit the nature / character of the car (IMO) as it was too dramatic sounding even at low speeds.

I finally switched over Akrapovic , not only to unleash the remaining potential of an already S/C'd engine , but also as a Step 1 to making my M3 race-prepped for the upcoming F1 track at New Dehi,India.

The setup I have is a straight pipe from the header to the back with the Akrapovic mufflers. Drone is almost zero and the car is certainly very easy to drive around town with no overwhelming exhaust notes at low speeds.

At high speed the exhaust sounds awesome! Very metallic in nature . There is a noticeable increase in power and throttle response between 3-6k rpm.


I did however notice something strange however. After 3.5K rpm, there is a certain hissing sound coming from the back of the car. It sounds very much like the intake sucking air sound , but is definitely coming from the back of the car , so I attributed it to the exhaust. Now this is my first time with a straight pipe setup , so I was a little concerned. Although the sound is very likable by me , I want to be sure it is not abnormal. It comes on around 3-4K rpm and is very distinct, even with the windows rolled up and is audible only when the throttle is pressed. If I release the throttle , the hissing sound goes away.

I am going to take the car to the workshop tomorrow and try to see if there are any fitment issues , but would love to get input from fellow members on what this could be.
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      11-12-2010, 05:34 PM   #2
duk
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Wow congrats, pls keep us informed.
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      11-13-2010, 02:18 AM   #3
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Quote:
Originally Posted by ecksreturns View Post
Hi guys.

I did however notice something strange however. After 3.5K rpm, there is a certain hissing sound coming from the back of the car. It sounds very much like the intake sucking air sound , but is definitely coming from the back of the car , so I attributed it to the exhaust. Now this is my first time with a straight pipe setup , so I was a little concerned. Although the sound is very likable by me , I want to be sure it is not abnormal. It comes on around 3-4K rpm and is very distinct, even with the windows rolled up and is audible only when the throttle is pressed. If I release the throttle , the hissing sound goes away.

I am going to take the car to the workshop tomorrow and try to see if there are any fitment issues , but would love to get input from fellow members on what this could be.
I have take the same exhaust(pictures here http://www.m3post.com/forums/showthread.php?t=435942 ) with yours 1 week ago. it does the same noise in the same rpm dont worry. OR BOTH we have a problem
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      06-27-2012, 11:44 AM   #4
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I put on the AKRA Evolution recently... I also put on the Macht Snell Stage 2 filter/duct at the same time. I immediately noticed the engine sound coming back through the intake from 3-4K on my first drive (a loud raspy rattle/exhaust type sound that seems to be coming from right in front of the driver). I spent a good day trying to figure out if I had tightened down everything properly thinking it was an exhaust leak. But under full throttle, the sound would only happen from 3-4K - if it was a leak I would heard a sound across the RPM band... Being that I work as an air induction designer for Ford Motor Co., I started wondering whether the sound was actually engine noise transmitting back through the intake. We put resonators on the air induction path of every engine made to cancel out unwanted engine frequencies - there aren't any on the M3 and this is my guess as to the problem. The smaller original inlet helped squelch some of the sound, along with the more restrictive exhaust. Now that air flow is much improved, the sound is very noticable.

I then removed my new duct/filter from Macht Snell, put back on the stock filter and more restrictive duct to the intake - the sound was muted and definitely a bit quieter. Unfortunately, I could not take the loss of power and immediately put it back on. The only real test I didn't want to undertake was swapping the exhaust back to stock to really take a listen. So... I'm living with it, and I appear to be the only one in the car who notices it...


Quote:
Originally Posted by stefanos-ktm View Post
I have take the same exhaust(pictures here http://www.m3post.com/forums/showthread.php?t=435942 ) with yours 1 week ago. it does the same noise in the same rpm dont worry. OR BOTH we have a problem
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