[tartopomme]

335i exhaust valve in the left muffler , why ?

[SROC3]

this is so that under low rpms, there is enough back-pressure to give you more low-end torque. When enough pressure builds up the valve opens and both exhausts are utilized.

Hope this answers your question

great "traction control" avatar by the way!!!

[tartopomme]

I am not sure because when i start my engine, i checked :

cold engine a idle : closed
hot engine at idle : open

why ?

[SROC3]

I think that it actually does that too so that the back pressure adds to the ability of the engine to heat up more effectively. The valve may seem open, but is not completely open until the car reaches a certain rpm range. Its all about back pressure to give more torque at lower rpm ranges.

[SteveMD]

It has nothing to do with back pressure, torque or power. It is to reduce noise at low RPMs.

Do a search for 'Golf Tee Mod' and knock yourself out.

[Chio]

totally agree with SteveMD I have the golf tee mod done now and it is just louder. the response and everything is great! if anything it feels better!

[m3power13]

I tend to agree with SROC3. Many of todays in-line 4 sportbikes use the exact type of butterfly valve in their exhaust. It is used to control power at various RPM ranges, through backpressure. I highly doubt it is because of sound related issues. There is a video on the forum displaying the sound after using the golf-tee mod and the car hardly sounds different.

Also, many folks on the forum who have done the golf-tee mod have reported negative throttle response and loss of low-end grunt. This is the exact symptom those in the motorcycle world have experienced when removing their butterfly valve from the exhaust.

It makes no sense that it would be for sound. The E46 330i sounded amazing when started up at idle, a deep intoxicating sound. The 335i sounds blah in my opinion. If anything it needs to be louder.


BTW, Chio, you have had an amazing collection of BMW cars. :rocks:

[tartopomme]

cold engine a idle : closed
hot engine at idle : open

warm up of the cat ? no ?

[m3power13]

Originally Posted by tartopomme

cold engine a idle : closed
hot engine at idle : open

warm up of the cat ? no ?

That sounds logical also.

[tartopomme]

If it was for the sound, at idle hot engine the valve will be closed too.

[SteveMD]

Do a search. It is mentioned in BMW training.

It is to reduce noise at low RPMs.

For an E46 but here you go: http://autorepair.about.com/library/a/1d/bl104d.htm

The electrical function of the exhaust flap operation is controlled by the MS 41.1 module.

At idle speeds, up to 2500 RPM: the exhaust flap is closed with vacuum applied to the actuator. This causes the exhaust gas to pass through the long resonator pipe, reducing the low frequency noise that is generated.

Above 2500 RPM: the exhaust flap opens. This allows the exhaust to pass through the short pipe which maximizes the back pressure effect to provide the best performance.

In the event of electrical or vacuum failure the flap will rest in the open position providing maximum exhaust throughput.

Therefore plugging the pipe simulates a vacuum failure and provides max back pressure.

It's for noise reduction. Specifically low frequency resonance at low RPMs that some less informed 'near-luxury' car drivers may not be too keen on. Not all 3 er owners want to cut the zorst off at the headers like us

Golf tee it and the car sounds great at idle.

[Chio]

I was at the dealer this week and we had to 335 with the same about of miles the other one did not have the Golf tee mod. Mine was a little louder and when you drive on the highway you can also hear it more not much at all. in the morning this thing sounds like a bear growling it is killer with both pipes open..

If you dont believe me try it and report back...

[tartopomme]

I don't try because at idle my valve is open (warm engine), no need the golf tee.

I rev the engine and check the valve, the valve is always open.

On my car, the valve is only closed at start with clod engine.

[vAnt826]

Why the hell would you want back pressure from your exhaust anyway?

It seems like there are many people who just keep reposting it, but don't know why.

There is a reason why upgrading your exhaust to a much more free flowing exhaust gives you more power. LOW END AND TOP END.

Logically I can't grasp the concept that plugging your exhaust gases will give you more power.

[OpenFlash]

Exhaust backpressure is always an evil thing in turbo engines. Turbos are powered by the pressure differential between both sides of the exhaust turbine. The bigger differential, the better response time. You want max exhaust pressure on the inlet side of the turbine. For the most part, you do this by sizing the runners in the exhaust manifold properly and by coupling the turbo as close as possible to the exhaust port. The exhaust pressure on the other side of the turbine is kept low as possible by simply using the least restrictive exhaust system possible given the set of real-world constraints (noise, emissions, fitment, etc,.)

Cheers,
shiv

[SteveMD]

Originally Posted by vAnt826

Why the hell would you want back pressure from your exhaust anyway?

It seems like there are many people who just keep reposting it, but don't know why.

There is a reason why upgrading your exhaust to a much more free flowing exhaust gives you more power. LOW END AND TOP END.

Logically I can't grasp the concept that plugging your exhaust gases will give you more power.

Again, the valve is not there for varying back pressure. It is there to reduce noise.

[Chio]

SteveMD is right when i start the car up in the morning the drivers side is 2x as loud as the pass. side.

[bnj]

And this is a brilliant solution. Shows some class. There is a difference in Bmw and rícer performance. You do not need to sacrifice to sound like a ricer but you are still faster as it does not hold you back at all, when you want to GO.

[SROC3]

Shiv?

[bnj]

The exhaust diameter requirement depends on the power. Below 2500 rpm half of the exhaust system volume is non-restrictive and at that point any additional volume is not going to help. As Shiv said, the backpressure is always evil - never good, but at very low revs, there is no back pressure. The back pressure emerges along the high power output / high flow from the engine. Then you need to have a large non-restrictive exhaust.

[Chio]

Originally Posted by bnj

And this is a brilliant solution. Shows some class. There is a difference in Bmw and rícer performance. You do not need to sacrifice to sound like a ricer but you are still faster as it does not hold you back at all, when you want to GO.

It gives the car a nice sound and whythe hell would i want to make it sound like a "ricer"!! As for class it does not sound much louder than stock just better. GEEZZ!!! This is a mod that had been done by the the E46 guys for sometime. I just got off of the phone with a master BMW tech and it is only for sound.
the same this was on the S4 when they were first produced it was just for sound and it really does not change that much then about 3 months in they deleated it.

[Chesmu]

Originally Posted by SteveMD

It has nothing to do with back pressure, torque or power. It is to reduce noise at low RPMs.

Do a search for 'Golf Tee Mod' and knock yourself out.

forget golf tee... calvino has done this in the 330...it's in the diy section.