[Berzerker]

Originally Posted by Info@mad-us.com

When the valves are closed 100% of the flow is traveling through the muffler. The size and packing material in the muffler will dictate how loud it is.

What he is suggesting is allowing some of the exhaust flow to travel through the muffler naturally even when the valves are fully open so that it regulates the sound and it's not just a raspy straight pipe. Bmw is doing this by closing down the valves to around 40% in (open mode) and forcing the air into the muffler causing some back pressure in the process.

The result would be similar to adding a resonator inline that is always doing its job regardless of the valve angle.

Doesn't this happen naturally anyway? I would imagine some of the air, even with the valves fully open, is still going through the muffler a bit since that pathway isn't closed off when the valves are opened. I understand more air would go through if the valves weren't fully open but I don't really understand what would change otherwise differently than what BMW does OEM-style.

[Info@mad-us.com]

Originally Posted by Berzerker

Doesn't this happen naturally anyway? I would imagine some of the air, even with the valves fully open, is still going through the muffler a bit since that pathway isn't closed off when the valves are opened. I understand more air would go through if the valves weren't fully open but I don't really understand what would change otherwise differently than what BMW does OEM-style.

I'm sure it does. It's more about offering a aftermarket system that takes some of the great things the oem muffler has to offer and just making it more suited for modified downpipes and midpipes.

The stock system gets pretty raspy with a midpipe and downpipes with valve 100% open.

It may be a nice option for those looking for more tone vs volume.

[cozye]

I’m thinking that the impact to having a larger connecting pipe to theoretically allow more exhaust through the muffler with the valves fully open will have a negligible effect. At that point in the exhaust system, there is no more restriction or back pressure at all, the exhaust is going to take the path of least resistance, and the path is already open to the muffler anyway. Increasing the size and direction of the pipe I don’t think would make any perceivable difference, unless you partially close the valve, which could easily be achieved by programming the valve controller to a partially closed amount. Or just leave the valves in the OEM position? They do open up some on hard throttle anyway.. Driving this setup myself with the AWE switchpath, I cannot think of any advantage of having the valve open “quieter” option of being an advantage. If I want it quieter I just put it back in OEM mode, and its still sporty when accelerating sufficiently

[Info@mad-us.com]

Originally Posted by cozye

I’m thinking that the impact to having a larger connecting pipe to theoretically allow more exhaust through the muffler with the valves fully open will have a negligible effect. At that point in the exhaust system, there is no more restriction or back pressure at all, the exhaust is going to take the path of least resistance, and the path is already open to the muffler anyway. Increasing the size and direction of the pipe I don’t think would make any perceivable difference, unless you partially close the valve, which could easily be achieved by programming the valve controller to a partially closed amount. Or just leave the valves in the OEM position? They do open up some on hard throttle anyway.. Driving this setup myself with the AWE switchpath, I cannot think of any advantage of having the valve open “quieter” option of being an advantage. If I want it quieter I just put it back in OEM mode, and its still sporty when accelerating sufficiently

Speaking on aftermarket systems. There is a difference in testing using a 90 Deg connecting pipe compared to Y pipe style angled connecting pipe. A higher % will run through the muffler.

Piping diameter is likely to not have as much of an impact on sound however, for those wanting less restriction in a closed valve mode an angled connecting pipe and a larger diameter is going to be positive.