VTT Breather Cap Review

[matreyia]

Ok folks, here are my impressions and observations on the VTT Breather Cap after a month of usage.

1. no adverse effects noticed
2. no butt dyno gains felt
3. no smells
4. makes your bay look 'nonstandard' (good or bad is subjective)
5. installation is easy
6. engine temps not affected
7. engine revving behavior did not change in any way

I installed it because the marketing said that it helps with turbo oil drain, 'free up hp' <---- whatever that means, reduce valve cover pressure under boost.
I will keep it long term and see if any benefits are felt over stock cap. Here is a clip of what it looks like and additional comments about it.

 

[gmagnus7]

I have the cowl delete filters and started to smell fumes after I installed this. Once I upgraded my PCV valve like 90% of the smells went away, so I think the breather was in fact doing it's job and the stock PCV wasn't working very well to begin with (it had <5000km on it).

 

[matreyia]

I have the cowl delete filters and started to smell fumes after I installed this. Once I upgraded my PCV valve like 90% of the smells went away, so I think the breather was in fact doing it's job and the stock PCV wasn't working very well to begin with (it had <5000km on it).

I had the bms cowl filters before, but my cowl plate kept breaking in half due to the m3 cowl cutting modifications and water got into cylinder 6 spark plug and rusted it out. so now I replace all cowling with stock. I like the quieter ride too. The car is almost stock like and has the comfort of bmw except for when you mash the pedal and poop your pants.

 

[gmagnus7]

I had the bms cowl filters before, but my cowl plate kept breaking in half due to the m3 cowl cutting modifications and water got into cylinder 6 spark plug and rusted it out. so now I replace all cowling with stock. I like the quieter ride too. The car is almost stock like and has the comfort of bmw except for when you mash the pedal and poop your pants.

I'm actually planning to go back to the stock cowl too, just have to pull one from the junk yard. Mainly for aero reasons.

 

[E92-Ghandi]

I just installed this yesterday, didn't feel any difference either. I love the way it shows in the engine bay.

 

[fmorelli]

Squirrel factor - might look good with an Oetiker clamp.

Filippo

 

[matreyia]

Squirrel factor - might look good with an Oetiker clamp.

Filippo

Nope. Needs to be removeable.

 

[Gavin]

I wonder under load how much boost is being relieved through the cap,all of it?if so then that's a big plus

 

[matreyia]

I wonder under load how much boost is being relieved through the cap,all of it?if so then that's a big plus

No idea. But probably enough to let the engine not be as stressed as if it were capped. I mean my car doesn't feel like it's stopped up when I slam the pedal now like it used to feel. It just revs without incident or delay.

 

[gmagnus7]

I wonder under load how much boost is being relieved through the cap,all of it?if so then that's a big plus

If your PCV is functioning properly it should be zero, but most people don't have a properly functioning PCV system lol.

 

[matreyia]

If your PCV is functioning properly it should be zero, but most people don't have a properly functioning PCV system lol.

So in theory, it should not do anything if the car is healthy and is only there for backup safety?

 

[The Convert]

So in theory, it should not do anything if the car is healthy and is only there for backup safety?

Correct. It’s a fail safe so to speak.

 

[gmagnus7]

So in theory, it should not do anything if the car is healthy and is only there for backup safety?

Exactly. I personally think it's a good idea regardless of PCV setup. Especially with how sensitive the turbo drains are to PCV problems and crankcase pressure.

 

[iminhell1]

If your PCV is functioning properly it should be zero, but most people don't have a properly functioning PCV system lol.

Put some more thought into that.
What is the % of blow-by under load? (under stock conditions)
What happens when more boost/more timing (more cylinder pressure) is introduced? same percentage of blow-by?
How is the orifice of the PCV figured? (what it the flow limitations, vs time)


You'll find that the stock PCV is fine for low boost and moderate cylinder pressure if the rings are in good shape.
On older engines with miles and use, there needs to be more flow through the system to relieve the pressure in the crank case.

You also have to take into consideration if there is ANY vacuum leaks. The vacuum pump will quickly overwhelm the PCV. So leaks are a huge deal on this engine.
If the vacuum pump where external, not a big deal.

 

[gmagnus7]

Put some more thought into that.
What is the % of blow-by under load? (under stock conditions)
What happens when more boost/more timing (more cylinder pressure) is introduced? same percentage of blow-by?
How is the orifice of the PCV figured? (what it the flow limitations, vs time)


You'll find that the stock PCV is fine for low boost and moderate cylinder pressure if the rings are in good shape.
On older engines with miles and use, there needs to be more flow through the system to relieve the pressure in the crank case.

Lol okay. I put more thought into it and came to the same conclusion. How the hell can you expect someone to know the % of blowby, or the in-depth design of the PCV valve? I'm not a BMW engineer. Obviously with increased cylinder pressure there is more blowby as the pressure differential between the combustion chamber and crankcase is greater. Compression and leakdown tests are fine on my ~60k mile engine suggesting my rings are in good condition, and I'm not running crazy high amounts of boost. I had simply stated that the stock PCV valve (that was practically brand new) was allowing pressure to build up in the crankcase. Once I installed an upgraded PCV valve there was no more crankcase pressure, simple as that. I'm not saying that in "theory" the PCV is fine like your somewhat condescending comment, I'm saying that in reality it wasn't. Lot's of information on how garbage the stock PCV system is on these cars so how about you go do some research.

 

[fmorelli]

Usual problem. Measurements are necessary with a good understanding of how vacuum works on these cars. Seems that precious few have full command of both (myself included) and are speculating.

Filippo

 

[Jeffman]

I’ve had the VTT oil cap breather since it was introduced - what, two years now? I can’t seem to tell whether it’s doing anything. I’ve never seen any oily residue on the outside which would tell me there’s venting. It’s completely clean. I have stock original turbos pushing 22-23 psi, and I have both low and high side catch cans with RB PCV valve.

 

[The Convert]

I’ve had the VTT oil cap breather since it was introduced - what, two years now? I can’t seem to tell whether it’s doing anything. I’ve never seen any oily residue on the outside which would tell me there’s venting. It’s completely clean. I have stock original turbos pushing 22-23 psi, and I have both low and high side catch cans with RB PCV valve.

If you have a boost gauge that also measures vacuum and can reroute the reference line to a fitting in your VC, you’d be able to to watch and see if you’re seeing any pressure build in your crankcase. Typical way to do this is with a fitting in the oil cap though...

 

[Jeffman]

Good point. But I’m not messing with my valve cover. It took me an entire weekend two years ago to replace it.

 

[fmorelli]

Good point. But I’m not messing with my valve cover. It took me an entire weekend two years ago to replace it.

lol ... I just did my son's 335is last weekend. PITA for a valve cover gasket, for sure. Lots of little tricks, though, as you do them several times - those can really make a difference. This is one of the places I like my Z4 - sooooo much more room.

Filippo