Valvetronic and golf tee mod question

[chris82]

I was browsing around on YouTube and came across this video where a guy comments this. (I take no credit for this information):

BMW's response to the purpose of the flapper is that it is for noise reduction ( as with the 5 series), but in a mechanical perspective it is also necessary for the flapper at lower RPM's (under 2000) because the Motor is valvetronic and needs back pressure at lower RPM to aid with a faster tourque climb. This mod doesn't really sound much better and it causes the car to need higher RPMs to get to peak torque. If you need better sound from your 128 you should really go with an exhaust package."

That was a comment on this video:

Is that a valid statement?

Thanks

[Overpar56]

I would say bunk. From what I understand the performance exhaust doesn't have the flapper and just plugs the vacuum line into a fitting that goes nowhere.

I've noticed nothing different in power with it plugged. As for sound, it's not a lot different except at lower RPM.

[631twentyeighteye]

Ive ran with and without the flapper multiple times and have noticed nothing except for noise difference. He doesn't know what he's talking about.

[Pothole]

Originally Posted by Overpar56

I would say bunk. From what I understand the performance exhaust doesn't have the flapper and just plugs the vacuum line into a fitting that goes nowhere.

I've noticed nothing different in power with it plugged. As for sound, it's not a lot different except at lower RPM.

For the 125i the PE does have a flap.



Pic of my BMWPE.

[Dafttt]

Originally Posted by Pothole

For the 125i the PE does have a flap.

Kind of an oxymoron, isn't it? Glad you golf tee'd, those cold starts are half the fun.

[Dackelone]

Originally Posted by Overpar56

I would say bunk. From what I understand the performance exhaust doesn't have the flapper and just plugs the vacuum line into a fitting that goes nowhere.

I've noticed nothing different in power with it plugged. As for sound, it's not a lot different except at lower RPM.

Originally Posted by Pothole

For the 125i the PE does have a flap.



Pic of my BMWPE.

I think @Overpar56 was talking about the 135i PE vs OE exhaust. Yes, the 128i has a flapper valve even on the PE.

[Pothole]

Originally Posted by Daft Auto

Kind of an oxymoron, isn't it? Glad you golf tee'd, those cold starts are half the fun.

They really are! Love that sound! Also lifting off the gas really gives a nice gurgle.

Originally Posted by Dackelone

I think @Overpar56 was talking about the 135i PE vs OE exhaust. Yes, the 128i has a flapper valve even on the PE.

Ah thanks! I did not know that

[Dafttt]

Originally Posted by Dackelone

I think @Overpar56 was talking about the 135i PE vs OE exhaust. Yes, the 128i has a flapper valve even on the PE.

No flaps on mine. The hose connects to a dummy and doesn't seem to go anywhere.

[Pothole]

Originally Posted by Daft Auto

No flaps on mine. The hose connects to a dummy and doesn't seem to go anywhere.

Maybe the 128i version differs from 125i? Or maybe it's US spec?

No worries, you don't need it anyway.

[TheSt|G]

Also deleted the valve on the Supersprint muffler. I highly doubt they are making something that lost power.

[Dafttt]

Originally Posted by Pothole

No worries, you don't need it anyway.

Haha, rock on PE brotha!

[Dackelone]

Originally Posted by Daft Auto

No flaps on mine. The hose connects to a dummy and doesn't seem to go anywhere.

I think your right. Not sure why @Pothole 's PE has it. ?


Here is a great DIY for a PE on a 128i and what it takes. @MikeinAlexandria great DIY....

DIY: BMW Performance Exhaust on 128i cabrio
http://www.1addicts.com/forums/showthread.php?t=450937

[TheSt|G]

Originally Posted by Dackelone

I think your right. Not sure why @Pothole 's PE has it. ?

Perhaps TUV regs as Pothole is in the EU?

[Pothole]

I ordered mine from leebmann24.de. Germany that is, so TUV regs sounds plausible.

The fact that daft auto´s PE doesn´t have a flap pretty much wraps up this discussion..

[128Convertibleguy]

Originally Posted by Chrisar82

"...but in a mechanical perspective it is also necessary for the flapper at lower RPM's (under 2000) because the Motor is valvetronic and needs back pressure at lower RPM to aid with a faster tourque climb."

Is that a valid statement?

Thanks

Just adding information, not trying to change anyone's mind about anything.

There's been some talk about "backpressure". The purpose of restricting an exhaust at low rpm is not to add backpressure. Exhausts don't need backpressure. What they need is velocity. The momentum of exhaust can help scavenge the cylinder, and is used for that purpose. The performance linked purpose of restricting an exhaust at low rpm is to maintain velocity.

I have no clue whether the BMW flapper, at the very end of the system, does anything for that. But it's not impossible that it does. Some people have reported a perception that the golf tee mod reduces power at low rpm. Maybe they're wrong. Or maybe it does. The issue is not settled for me. For me, only a carefully done dyno test would settle it.

The above discussion applies to NA engines, only. I have no clue about turbo engines, I suspect it's a different story.

[Dafttt]

Originally Posted by 128Convertibleguy

Just adding information, not trying to change anyone's mind about anything.

There's been some talk about "backpressure". The purpose of restricting an exhaust at low rpm is not to add backpressure. Exhausts don't need backpressure. What they need is velocity. The momentum of exhaust can help scavenge the cylinder, and is used for that purpose. The performance linked purpose of restricting an exhaust at low rpm is to maintain velocity.

I have no clue whether the BMW flapper, at the very end of the system, does anything for that. But it's not impossible that it does. Some people have reported a perception that the golf tee mod reduces power at low rpm. Maybe they're wrong. Or maybe it does. The issue is not settled for me. For me, only a carefully done dyno test would settle it.

The above discussion applies to NA engines, only. I have no clue about turbo engines, I suspect it's a different story.

The closed flap increases back pressure. It's there to keep the car quiet, limit fumes, and warm the cats on a cold start.

[Taskmaster]

Originally Posted by Chrisar82

I was browsing around on YouTube and came across this video where a guy comments this. (I take no credit for this information):



That was a comment on this video:

Is that a valid statement?

Thanks

False.

[chris82]

Originally Posted by 128Convertibleguy

Just adding information, not trying to change anyone's mind about anything.

There's been some talk about "backpressure". The purpose of restricting an exhaust at low rpm is not to add backpressure. Exhausts don't need backpressure. What they need is velocity. The momentum of exhaust can help scavenge the cylinder, and is used for that purpose. The performance linked purpose of restricting an exhaust at low rpm is to maintain velocity.

I have no clue whether the BMW flapper, at the very end of the system, does anything for that. But it's not impossible that it does. Some people have reported a perception that the golf tee mod reduces power at low rpm. Maybe they're wrong. Or maybe it does. The issue is not settled for me. For me, only a carefully done dyno test would settle it.

The above discussion applies to NA engines, only. I have no clue about turbo engines, I suspect it's a different story.

Very interesting. Thanks for the input

[hotwheels]

PE for European 125i and 135i has the flap.
PE for American market does not have the flap.

I have an American PE for my 125i and it does not have the flap
Incredible sound.

No issue for valvetronic

[chris82]

Originally Posted by Daft Auto

The closed flap increases back pressure. It's there to keep the car quiet, limit fumes, and warm the cats on a cold start.

Forcing the exhaust gases through a smaller pipe would increase the velocity at which the gases flow out of the exhaust, thus the smaller exhaust acts as a 'vacuum', scavenging the gases from the cylinder. This would be used for lower RPM, but at higher when the engine produces more gases the exhaust opens back up.

This is starting to make sense. Only question is why would the PE not have it for US 128i?

[Dafttt]

Originally Posted by Chrisar82

This is starting to make sense. Only question is why would the PE not have it for US 128i?

Because it's useless and moot.

Thank you for your email to BMW Customer Information.

We can advise that the exhaust flaps adjust at differing engine speeds in order to make the most effective use of the exhaust silencer. When the vehicle is running at idle or at low RPM, the flap ensures that the exhaust gases use as much of the silencer's volume as possible, keeping exhaust noise down, e.g. when you're in slow traffic or driving in high gear.

Whereas when the vehicle is running at high RPM, the exhaust flow characteristics are adjusted by the flap to give the exhaust gases a more direct route through the silencer, thus using less of its volume. This also has the effect of allowing the engine to rev more freely as there is less restriction on the exhaust flow.

The primary reason for the flap is to make the most effective use of the exhaust silencer volume at differing engine speeds.

We trust this information is of some assistance to you but if we can help you further at any time, please do contact a member of the BMW Customer Information Team.

Yours sincerely

BMW Group UK
Elfriede McNeal
Product Information Advisor

Ellesfield Avenue
Bracknell
RG12 8TA

Tel: 0800 325600
Fax: 0870 5050 206
Email: customer.information@bmw.co.uk
Website: www.bmw.co.uk

[chris82]

We need to identical 128i. One with golf tee one without. Have someone test drive them without telling them which one is golf tee'd and see which they think is faster. Elimate the placebo effect