Can you hear your blow off?

[SlicktopTTZ]

Originally Posted by imported_mega

I can hear it on my n54 but only if I'm passing and was almost at redline and between gears when the car I'm passing is right next to me

my car is bone stock

I like to do it next to highway barriers.

[woner]

I hear it all the time. Its louder now with bms stage 1. Also, if I blip the throttle in first the cars makes an awesome crackling sound as the rpms drop. The stock exhaust on the n55 sounds great, I just wish it was a bit louder.

[RPM90]

Just for clarity sake, because things get promoted in these forums as if gospel.

I'm sure you guys are hearing what you say you hear.
However, you are not hearing a "BOV", like a classic atmospheric type. I know some of you know this, but it seems some don't get this.

A real atmosphere BOV is night and day difference in sound and volume compared to a recirc DV/BOV.
With a DV the pressurized air is not being "blown off", it is recirculated, or returned, into the intake path. An atmosphere BOV does indeed blow off/out the pressurized air to atmosphere. That's why it's so much louder, and cooler.

Given that the N55 has no throttle plate, as it uses valvetronic intake control, it really is a unique system. With a standard throttle plate, once the plate is closed, the pressurized air leaves the BOV or DV, so that there is no more pressurized air going to the intake manifold. But, with valvetronic, the air intake to the combustion chamber is controlled by the action of the intake valves. So, imagine them as individual "throttle plates". This probably also adds to why the N55 can should hold boost better in between shifts, even with a manual trans.

I need to look into how this N55 engine works, more closely.
I'd also think that the DV is located in a different area compared to the N54. The location of the N55's DV could also lend to hearing it better/louder.

[jhuber]

If you like the sound get BMS DCI and an active autowerke blow off valve, you will have no trouble hearing that pshhh sound with that set up

[Xyloft]

Originally Posted by ErvGotti

BMW uses an TMAP instead of MAFS sensor. It judges pressure instead of volume allowing us to use BOV's without a problem. Alot of people run BOV's on the N54

in addition to having different types of sensors, there are two types of BOV's: internal (recirculating) and external (atmospheric).

if an external BOV is after the MAF sensor, you would run rich, since the BOV has just released metered air outside of the intake track. the STI intake setup is like this and it sounds like the VW Audi scene is similar. I belive the 4g63 (evo, eclipses etc) uses a MAP sensor and does not have a problem using an external BOV.

there is probably a few baffles/silencers on your intake track that help quiet the intake noise. if you can find/remove/replace them i'm sure the pressure release noise will get louder.

http://en.wikipedia.org/wiki/Blowoff_valve has a pretty solid descriptoin of the different types and intake setups

[1SerieStud]

Actually I can vouch for 4g63's...they also have a MAF sensor right at the intake mouth so no, you cannot properly run a bov vented to the atmosphere unless the car undergoes a tune to compensate for the loss of metered air. Otherwise, it runs rich in between shifts.

Originally Posted by Xyloft

in addition to having different types of sensors, there are two types of BOV's: internal (recirculating) and external (atmospheric).

if an external BOV is after the MAF sensor, you would run rich, since the BOV has just released metered air outside of the intake track. the STI intake setup is like this and it sounds like the VW Audi scene is similar. I belive the 4g63 (evo, eclipses etc) uses a MAP sensor and does not have a problem using an external BOV.

there is probably a few baffles/silencers on your intake track that help quiet the intake noise. if you can find/remove/replace them i'm sure the pressure release noise will get louder.

http://en.wikipedia.org/wiki/Blowoff_valve has a pretty solid descriptoin of the different types and intake setups

[Atropos]

with the windows down, yes.

[RPM90]

Originally Posted by 1SerieStud

Actually I can vouch for 4g63's...they also have a MAF sensor right at the intake mouth so no, you cannot properly run a bov vented to the atmosphere unless the car undergoes a tune to compensate for the loss of metered air. Otherwise, it runs rich in between shifts.

My 1990- 1st gen 4g63 sure did have an OEM BOV.
It sounded very cool.

In later uses, like the EVO, they changed to DV.
The 4g63 was put to pasture a couple years back.

[Xyloft]

Originally Posted by 1SerieStud

Actually I can vouch for 4g63's...they also have a MAF sensor right at the intake mouth so no, you cannot properly run a bov vented to the atmosphere unless the car undergoes a tune to compensate for the loss of metered air. Otherwise, it runs rich in between shifts.

Originally Posted by RPM90

My 1990- 1st gen 4g63 sure did have an OEM BOV.
It sounded very cool.

In later uses, like the EVO, they changed to DV.
The 4g63 was put to pasture a couple years back.

Thanks for the clarification guys my 2nd gen DSM was NA, so I wasnt too sure.

[Sylon]

Im still confused, lol. Anyone have a parts listing on the N55 engine or something? WTF does my car have? haha

[MarkR171]

Originally Posted by Sylon

Im still confused, lol. Anyone have a parts listing on the N55 engine or something? WTF does my car have? haha

Check realoem. They have the F10 535i with N55 engine.

[The1]

I have the DCI intake, i definitely hear the air being let back into the manifold. even just casual driving i hear it, but obviously way more noticiable at WOT.

as someone else said, it's a bit of a sneeze sound.

and yes, someone else was curious if it was louder with a tune. yes, when switching between maps on my JB3 you can hear it more clearly the higher the map. and you can also hear it spool up more the higher the map as well. when running maps 5 or 7, it whistles away nicely. (i like the sounds, but people more used to refinement might find the sound more invasive. my solution is for them to roll up the windows)

[RPM90]

Originally Posted by Sylon

Im still confused, lol. Anyone have a parts listing on the N55 engine or something? WTF does my car have? haha

It has a recirc-Diverter Valve type blow off, not a BOV that blows to atmosphere.

[shockin330i]

the n55 can not use the dci, and it does not have a bov. What you hear is the turbo spooling...

[woner]

the n55 can not use the dci, and it does not have a bov. What you hear is the turbo spooling...

The sound of a bov/dv is very distinguishable from turbo spooling. It's already been cleared up that our engines use dv's (diverter valves) which, to my understanding, operate much like bov's but do not vent to the atmosphere.

[BMW86]

I can't believe some of you guys think the 135i N54/N55 comes stock standard with a BOV!!

[1SerieStud]

Originally Posted by BMW86

I can't believe some of you guys think the 135i N54/N55 comes stock standard with a BOV!!

I can't believe you haven't gotten the point of this thread. Regardless of dv or bov, the whole point is on whether you can hear the blowoff/recirculation sound of the valve or not.

[thez99]

I cant believe its not butter!!!

[MarkR171]

Originally Posted by thez99

I cant believe its not butter!!!

[Jeef Beef]

Originally Posted by SlicktopTTZ

Ok, y'all must be deaf because I could hear the recircs release into the intake on my n54 stock. Don't tell people that they CAN'T hear it just because you don't know what to listen for.

Then, buy a tune, DCI and leave your cowling off. Sound like a breathing, sneezing, jet monster!

Synapse Synchronic coming up soon!

Yep, my DVs are freakin LOUD as with BMS DCIs. It's true that in stock form there was no noise whatsoever, but with the intakes, it does the full 'pssssstttttttttt-teeeeeuuuuuchhhhh' I love it when I drive through my uni on part throttle in 2nd gear, and then abruptly let off. Everyone turns around and expects an Evo/WRX, and instead they have this puzzled expression on their face as a bimmer drives past.

[The1]

I'm left the distinct impression that a lot of people in here don't know what a DV or BOV are. And as a result it seems like a lot of people are making stupid comments to one another.

Please stop busting each others balls about it. The difference between the 2 things isn't that big, so if someone makes a mistake and confuses them, do they really need the bad attitudes?

and to clear up for anyone who is lost on this subject.

A blow off valve normally vents directly out into open air, however there are semi-recurculating ones on the market that do half the air returned to the intake and half to the atmosphere. (i have not yet seen one available for our cars however)

A Diverter valve is basically a blow off valve, except, instead of letting air off to nowhere, it has a hose that goes back into the intake manifold, this can do 2 things for the car. 1, makes a much quieter operation, and 2, helps keep the car from running too rich between throttle on and off, and causing check engine lights, but it seems this isn't necessary on our cars so it's mostly for silencing purposes.

Generally the air filter box and the piping leading to the box have little baffles or resonators that are attached, this is to take away excess noise from engines. this is especially evident on the honda S2000 as a lot of people end up taking their cold air intake back off after they hear the car screeching. it is also the reason a lot of WRX/EVO folks put on cold air intakes because they like to hear the turbos spool and hear the Diverter Valve blow air back into the intake manifold, some however like the extra power.

I forget when DVs or BOVs were invented, maybe the 70s, but originally cars never had them and the result was a shorter turbo life and a lot of turbo lag between shifts as they help keep the turbo spinning at high speed for longer thus keeping them closer to their optimal boost range removing most of the lag.

Hope this helps a few people.

If anyone is still confused, don't be afraid to ask, we are all here to help each other and learn.

[The1]

Originally Posted by Jeef Beef

Yep, my DVs are freakin LOUD as with BMS DCIs. It's true that in stock form there was no noise whatsoever, but with the intakes, it does the full 'pssssstttttttttt-teeeeeuuuuuchhhhh' I love it when I drive through my uni on part throttle in 2nd gear, and then abruptly let off. Everyone turns around and expects an Evo/WRX, and instead they have this puzzled expression on their face as a bimmer drives past.

I like that expression. it just reminds me that i'm driving a car with a special engine and nobody knows what is under the hood