Sean,
I'd doubt that there would be anything like that amount of gas being moved through the breather, as the effective 'compression ratio' of the crankcase is very low.

If you hook up a pressure/vacuum gauge to the dipstick tube with the engine ticking over, the needle oscillates between about +2 psi and -1 psi, which fits with crankcase vacuum, with a good breather fitted, being less than 1 psi.

In fact, 60mm water gauge is less than 0.1 psi...

ken

Can anyone offer a convincing explanation as to why -0.1 psi under the pistons could have any measurable effect on the power output of an engine which has a BMEP around 125 psi?
( BMEP is the average pressure over a cycle in the combustion chamber of an engine. )

How it can improve starting is something else which escapes me.

i was just trying to save Taskos from hyperventilating

there is a displacement by the boxer set up what the breather needs to do is vent any excess blowby gasses via the carb without letting the pressure fluctuations mess with the carburation- No?

all i know is that good breather = clean drive.

When David got his long tool out and did the manomiter tests on our cars at reg day the blue one had a positive engine however it always started, leaked very little and was a rather strong engine. it was still going strong 9 yrs later on the way to Most where it kept up with Vick and Dot at 70mph mixing it with the nuts Belgian traffic

I believe that the vaccum was mainlydesigned for avoiding oil leakages on old/neglected engines.

BUT...
Theoreticaly...
Can anyone offer a convincing explanation as to why -0.1 psi under the pistons could have any measurable effect on the power output of an engine which has a BMEP around 125 psi?

At the issue of power losses, I think that if the system was airtight then the same underpressure would be overpressure depenging on stroke direction.
But if we take into account the gases escaping from the piston rings we may have a undessired and substantive possitive pressure.

In practice...
I find it harder to climb my local hill with a malfuncioning reniflard than a new one.

http://www.youtube.com/watch?v=8YlEpI00ouU

The BMW breather is the type fitted to the /5/6/7 boxers if I recall correct the reed valve modification was sold by Harman who did loads of stuff back in the day,they no longer trade.

Is the Visa reniflard the same as the 2CV one? If not, are they somehow compatible?
Wish you all a great weekend.

Ι would like to report that my plumbers one way valve didn't last for 1.000km.
The underpressure was 5cm at idling but zero to 3.000rpm.
So I've replaced the reniflard with a refurbished one according to Sean instructions.
Now it's 5-10 cm all the way.

The shower valve I fitted is still functioning even after several flat out trips to France and back,I don't seem to have as much oil loss/use so I guess it's okay.I would still like to rebuild the reniflard,just need to obtain a duff one to work on. Sean's method sounds a good route to follow.

How many would you like?

I'm going to do a decent pictorial thread showing how to rebuild one, I just haven't had the time at work to do it.