[The Nightman]

I need to tee into the ~1/2" OD plastic brake booster line to get the 330i's exhaust flap control working onto my 328i. I have the factory tee but I'm not sure how to splice into the plastic line:



I also don't think I can retrofit the 330i brake booster line because it has different connectors for the vacuum pump end.

I was thinking of heating the tube up to get it to expand but not sure if that'll work. Any ideas are appreciated

[lowrydr310]

First check and make sure your 330i exhaust flapper isn't rattling before you try to get it working. That was the case for mine. Under load at low RPM the flapper would rattle badly.

Fixed with a variation of the 'golf tee' mod, splicing the hose just before the flapper actuator and inserting the release pin from my new belt tensioner to block it off. Flapper stays open all the time now and there's a mildly deep tone now, nothing obnoxious even highway cruising.

[The Nightman]

Originally Posted by lowrydr310

First check and make sure your 330i exhaust flapper isn't rattling before you try to get it working. That was the case for mine. Under load at low RPM the flapper would rattle badly.

Fixed with a variation of the 'golf tee' mod, splicing the hose just before the flapper actuator and inserting the release pin from my new belt tensioner to block it off. Flapper stays open all the time now and there's a mildly deep tone now, nothing obnoxious even highway cruising.

Thanks for the heads up. How do you check for the rattle?

I had ran the 330i exhaust with the valve always open but cold starts and highway droning were too annoying with catless headers. I'm hoping that I can run the 330i exhaust again with manual control over the muffler valve.

[lowrydr310]

I have no idea how to test if it's rattling.

Didn't realize you have headers. With the stock catted manifolds there's no highway drone with the flap open.

[mattanderson]

I have been curious about this, as a "dual mode" exhaust is appealing.

For the wiring, are you just going to wire up a manual switch?

[Efthreeoh]

I'd cut the line first then warm the ends and insert the T-fitting.

[The Nightman]

Originally Posted by mattanderson

I have been curious about this, as a "dual mode" exhaust is appealing.

For the wiring, are you just going to wire up a manual switch?

Yup. Normally, the vacuum controller in the trunk receives constant 12v and the ground is controlled by the DME. When the controller is powered, it opens and allows vacuum to close the muffler valve. I was just going to get a toggle switch to control the valve. Maybe a relay is better?

Now knowing about the rattling issue though, I might keep the valve open by default and just shut it when cruising on the highway

[The Nightman]

If heating the plastic doesn't work, another alternative is to replace the hard plastic section with a silicone vacuum line, which I can tee into easily. I assume it won't collapse under vacuum because the 330i brake booster line has rubber sections, but who knows. I'm hoping the plastic line was chosen because it was cheaper or easier to assemble. Doesn't seem to be an issue on N54 examples

Rubber section on 330i brake booster line:


ECS silicone replacement brake booster line for N54:
https://www.ecstuning.com/b-ecs-part...025515ecs03kt/

DIY replacement with 3/8" ID hose:
https://www.e90post.com/forums/showthread.php?t=1406884

[fastboatster]

can you try a brake booster line from the n54 335i? n52 and n54 seem to have the same vacuum pump side connector.

[lowrydr310]

Originally Posted by The Nightman

Yup. Normally, the vacuum controller in the trunk receives constant 12v and the ground is controlled by the DME. When the controller is powered, it opens and allows vacuum to close the muffler valve. I was just going to get a toggle switch to control the valve. Maybe a relay is better?

Now knowing about the rattling issue though, I might keep the valve open by default and just shut it when cruising on the highway

If you have manual control the rattling might not be a problem, especially if you plan to just close it on the highway. It was just under heavy load at low RPM I'd hear the rattle like coming up the hill by my house at 25MPH. If left it in a lower gear at higher RPM I wouldn't hear it. I am going to plug the vacuum line back into the flapper now to see.

The 335 also has a flapper on one of the mufflers. Mine rattled worse than my 330. There's an aftermarket rebuild kit with an upgraded bushing, but not worth the $125 for a quiet(er) exhaust.

[The Nightman]

Originally Posted by The Nightman

I also don't think I can retrofit the 330i brake booster line because it has different connectors for the vacuum pump end.

For posterity, ruling out the 330i brake booster line as the 330i vacuum pump (11667519457) has a different barb from the 328i vacuum pump (11667558344).

Originally Posted by fastboatster

can you try a brake booster line from the n54 335i? n52 and n54 seem to have the same vacuum pump side connector.

Maybe, I had assumed the N54 routing would be too different from the N52 but I didn't compare them side by side. That would be a simple swap

N52:


N54:


I'll try heating up my existing plastic line and fitting the tee. If that fails, I'll replace the plastic section with a vacuum line. Just paranoid about a soft line collapsing so I'll stick to something that meets DOT FMVSS 106VL.

[The Nightman]

Originally Posted by lowrydr310

If you have manual control the rattling might not be a problem, especially if you plan to just close it on the highway. It was just under heavy load at low RPM I'd hear the rattle like coming up the hill by my house at 25MPH. If left it in a lower gear at higher RPM I wouldn't hear it. I am going to plug the vacuum line back into the flapper now to see.

I wish we knew the "logic" used by the DME to determine when to open and close the muffler valve.

It it's any easier, you can unplug the wire connector to the vacuum controller in the trunk to keep the valve open.

[mattanderson]

Originally Posted by The Nightman

I wish we knew the "logic" used by the DME to determine when to open and close the muffler valve.

That's my other question, has anyone retrofitted the valve and used the stock wiring/DME logic for a full OE retrofit? I haven't been able to find it, if so. I'm guessing we'd need to find the correct wire + possibly add some coding.