[LunarMyst]

My car makes a loud woosh sound under acceleration about 3/4 times when I push it, but it was quite till about 2 months ago. It sounds like I have an aftermarket intake, but I dont. 100% stock intake. Checked for leaks, none. No engine codes. Boost is at expected levels. No power gain/loss. Just more noise from. Any idea why this could be? Perhaps some charged air is supposed to get recirculated but it doesnt? AFAIK there is no intake resonator/silencer on these cars, air gets pulled straight into the intake box.

Car: 2013 335i manual M sport
Mods: JB4, downpipe, charge pipe, intercooler, light flywheel, gapped S55 spark plugs, MPE

[ae4007]

Might be a cracked intake pipe. happened to my car a while back and it made the intake sound very loud, if you follow the intake all the way down underneath the car, there is a spot where they break easily, very hard to spot unless you're underneath the car and have someone wiggle the intake from the top. When mine broke I took into the shop and the tech couldn't find it until I got underneath the car and pointed it out to him.

[LunarMyst]

Originally Posted by ae4007

Might be a cracked intake pipe. happened to my car a while back and it made the intake sound very loud, if you follow the intake all the way down underneath the car, there is a spot where they break easily, very hard to spot unless you're underneath the car and have someone wiggle the intake from the top. When mine broke I took into the shop and the tech couldn't find it until I got underneath the car and pointed it out to him.

Are you talking about charge pipe from intercooler to the intake maniforld? That one I upgraded and its not cracked or leaking. Or are you talking about intake pipe from filter box to the turbo?

[ae4007]

Originally Posted by LunarMyst

Are you talking about charge pipe from intercooler to the intake maniforld? That one I upgraded and its not cracked or leaking. Or are you talking about intake pipe from filter box to the turbo?

Intake pipe from filter box to the turbo

[SeanWRT]

I heard the woosh from 5k5~7k rpm, exactly like you described when I had a new tune a few months back. But at low and middle rev ranges, it was all fine and normal.

However the woosh was gone completely with a map update. I have to believe it had something to do with tuning.

Mine is a m2, the intake box has a hole opening at the bottom, identical to n55 MPPK.

[Mike@N54Tuning.com]

Originally Posted by ae4007

Intake pipe from filter box to the turbo

Thats a good place to check and also check for any boost leaks, but if you are holding boost properly I doubt that would cause a large woosh, as that would most likely cause a limp from boost to low code.

Does it do it on all maps? Map0?

Mike

[LunarMyst]

Originally Posted by ae4007

Intake pipe from filter box to the turbo

Checked intake tube, looks fine. Will hop under the car and check turbo inlet pipe when the weekend comes. Do you recall which part of it cracked for you? Is it around the point that connects it to the turbocharger? Somewhere in the middle maybe?

Originally Posted by SeanWRT

I heard the woosh from 5k5~7k rpm, exactly like you described when I had a new tune a few months back. But at low and middle rev ranges, it was all fine and normal.

However the woosh was gone completely with a map update. I have to believe it had something to do with tuning.

Mine is a m2, the intake box has a hole opening at the bottom, identical to n55 MPPK.

It is possible that the dealership updated ECU software at some point, but if anything, that would cause less noise. No?

Also checked my air filter box. Even though its an M sport model, the box has no opening for extra noise to be let out. (M sport PN - 13718616013)
It also initially came with regular air filter (PN - 13717602643), but when it was time to change, dealer installed M sport filter (PN - 13718616909). That should not affect the sound however.

My car is an early production F30 from 07/12 so maybe they did not have enough M sport intakes at the time? Not sure.

Originally Posted by Mike@N54Tuning.com

Thats a good place to check and also check for any boost leaks, but if you are holding boost properly I doubt that would cause a large woosh, as that would most likely cause a limp from boost to low code.

Does it do it on all maps? Map0?

Mike

Car hits 12-13 PSI on map 1 with 2 gals of E85 + 91 ACN. Makes noise in all maps, including 0, but the sound gets louder when boost is higher. Again, no error codes, no limp mode even after driving 150+ miles in map 0. When I dont push the car, there is no noise at all.

Thanks for replies guys! Really appreciate your input.

[ae4007]

Originally Posted by LunarMyst

Checked intake tube, looks fine. Will hop under the car and check turbo inlet pipe when the weekend comes. Do you recall which part of it cracked for you? Is it around the point that connects it to the turbocharger? Somewhere in the middle maybe?

Where it connects to the turbo

[ae4007]

It won't throw any error codes because the MAF is still reading air, it's just getting more air than the car thinks and sucking so much air causing the loud sounds

[Mike@N54Tuning.com]

Any updates?

Mike

[LunarMyst]

Unfortunately havent had the time to look under the car, but I put the engine cover back on, and it cut down on some of the noise which apparently came from injectors.

Still, the inconsistent intake noise is there half the time when the car is floored, but I dont hear it in 6th gear. Ever. Makes me wonder if its active sound pumping artificial noise into cabin. Tried to switch off active sound via JB 4 (menu 1) with no success. Need to look around the trunk also to see if my car has it, then try to disconnect it.

And of course check inlet pipe

Will keep u posted.

[LunarMyst]

So I did more digging around the internet and tried a few more things.

-Inlet pipe does not appear to be cracked.
-Some folks say their engines make more noise when running E85, so I tried running straight ACN 91
-Once again disabled JB 4
-Played more with comfort/sport modes
-Tried different ambient temperatures

In the end, it appears the humming noise is present between 2500-3000 rpms in sport mode, most pronounced in 5th gear, but comfort mode gives it less boost so it goes away.

My suspicion is that it has something to do with ignition noise due to ignition timing and pressure inside the cylinders. Upgraded spark plugs - NGK 97506 @ .22in, higher boost from JB4, and higher octane from E85 all contributed to this.

[LunarMyst]

Quick update after this thread got 2.5k+ views

Eventually it turned out to be resonance from light weight flywheel. New flywheel simply does not eliminate as much noise/vibration being passed from the engine through the drivetrain.
A partial fix for this is to use a thicker manual transmission transmission oil. This both quiets down idle gear chatter/rattle and helps with noise resonance.
Currently I run a combination of .5 qt Redline GL-5 75w140NS and 1.5 qt Redline MT90 and it eliminated about 60-75% of the noise compared to factory fill BMW oil.
It is worth noting that very thick gear oil makes shifting a cold gearbox harder, but after a warm up, it becomes smoother.

Hope that helps!

[n55david]

Originally Posted by LunarMyst

Quick update after this thread got 2.5k+ views

Eventually it turned out to be resonance from light weight flywheel. New flywheel simply does not eliminate as much noise/vibration being passed from the engine through the drivetrain.
A partial fix for this is to use a thicker manual transmission transmission oil. This both quiets down idle gear chatter/rattle and helps with noise resonance.
Currently I run a combination of .5 qt Redline GL-5 75w140NS and 1.5 qt Redline MT90 and it eliminated about 60-75% of the noise compared to factory fill BMW oil.
It is worth noting that very thick gear oil makes shifting a cold gearbox harder, but after a warm up, it becomes smoother.

Hope that helps!

Interesting.. thanks for the update. Hopefully it helps someone else we may come across the same thing.