02-25-2013, 07:47 PM | #45 | |
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02-25-2013, 08:47 PM | #46 |
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For me, difference is definitely there. I live on a small hill so I have to go up the ramp everyday. And that's where I can definitely feel a bit of a power gain. In short, comfort mode is like sport mode accel up ramp now
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02-25-2013, 09:16 PM | #47 |
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As long as you are happy and nothing is broken, I am happy.
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02-26-2013, 01:06 AM | #48 | |
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Overall, the exhaust note is more sonorous but the difference is not as significant compared to the same mod on the E92 335i I used to own. |
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02-26-2013, 02:40 AM | #49 | |
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Let's start from NA (yes I know. We are all turbos now. But bear with me for a little....) Back pressure actually prevents exhaust gas flow and and impedes proper scavenging on the engine cylinder cycles. What the NA engine needs maximum exhaust gas VELOCITY, so that it creates temporary vacuum which sucks out residual exhaust gas still in the cylinder. The easiest way is to squeeze the gas in a tube that is at the correct diameters. I did say correct, there is a sweet spot to tune the exhaust speed. If the pipe is too wide, the gas slows down and scavenging becomes less effective as the vacuum is not as long. If the pipe is too narrow, well, you have excess back pressure which makes it more difficult to suck residual gas out from the engine. This is also one of the reason why, when one simply replace exhaust systems on a NA car with bigger pipes, people will generally feel lost of low-end torque because the exhaust at low rpm is not moving fast enough for scavenging, hence engine is less efficient. Improper tuning and exhaust matching can also cause exhaust gas moving too fast, which sucks not only residual burnt gas, but also sucks out some of the air that just entered the chamber and unburnt fuel. So, in NA, simply replacing exhaust without adjusting engine tune almost always results in less performance....... Now for Turbo cars like ours, scavenging the exhaust gas out of the chamber is less of a problem. Why? Because we have blowers force feeding the chamber with compressed air!!!! And contrary to what people may say about back pressure "creating loads on the turbine to shorten spooling", that is not at all correct. The turbo units essentially is a turbine ran by differences between intake pressure and outflow pressure. The intake is from the exhaust manifolds from the engine and the outflow is everything back from the turbine. So if you create back pressure behind the turbine, it will make the turbine harder to turn, thus in turn makes turbo lag worse....... So the bigger the exhaust pipe from turbo-back, the lower the pressure (limiting up to atmospheric pressure in theory) at the turbine outflow port. In theory, the turbine fan should be easier to turn, and thus lowering spool time of the turbo? Is my understanding somewhat correct on this?
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02-26-2013, 12:59 PM | #50 | |
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Now, I wanna get X-Pipe for this thing, but something I can swap in and out myself without visiting the shop. |
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02-27-2013, 01:29 PM | #51 |
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Only the S63 engine has twin scroll turbos. The N63 settles for regular turbines.
The analysis re exhaust is correct. However, peak HP is controlled by max boost. There is no way holding open the exhaust flap is making more power. Perhaps there's a slight reduction of back pressure reducing turbo lag, but I doubt it's enough to feel. The louder exhaust note is just fooling your mind. |
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02-27-2013, 01:37 PM | #52 | |
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02-27-2013, 08:09 PM | #53 | |
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02-27-2013, 09:34 PM | #54 |
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Let me know if check engine light pops up because of that mod, so I can quickly remove it before sending it to the dealer.
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03-04-2013, 08:21 PM | #56 |
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If you jack your car up and lay on the ground while doing it, then it would be easier. Another trick is, pre-bend the zip tie, so you don't have to squeeze your hand through the crack between exhaust and diffuser to get it loop back.
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03-04-2013, 08:28 PM | #57 |
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So I just push the flap in with something and then tie the control arm to the nearest stationary piece? Holding the loop sounds effective, gonna hunt for a jack now asking all my neighbors since I'm in an apartment lol
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03-04-2013, 08:43 PM | #58 | |
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I used a piece of stick to yank the flap open and hold it open while installing zip tie. When flap is in open position, actuator arm will be in retracted position where you can loop zip tie around the link from actuator to the flap to keep it open. If you have trouble with zip tie which I did, then you can use some sort of steel wire instead. It would be easier with steel wire because you can easily bend it and it holds shape. Zip tie keeps swinging back even after I pre-bend it. |
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03-04-2013, 09:52 PM | #59 | |
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It sounded meaaannn on the cold start, and now at normal cruising it sounds a little louder with the same tone of stock, however it screams when you pass 3-3.5k+ Thanks Edit: Heres the result! http://a.yfrog.com/img14/2792/n3axka...ojnamdnphn.mp4 Last edited by markeh; 03-04-2013 at 10:13 PM.. |
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03-04-2013, 10:33 PM | #60 | |
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03-05-2013, 01:04 AM | #61 |
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It could get quite painful on the fingers holding the actuator while manipulating the zip tie in those tight crevices between the exhaust tip and the muffler. Glad that you pulled it off finally. Enjoy the result.
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10-15-2022, 01:22 PM | #62 |
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