QGMika

Any comment on this?

"Disclaimer: You may ignore this post if you dare, but you will be risking performance and engine damage.
I am not a BMW/MINI technician, but you should not reroute the PCV from a vacuum source to atmospheric only. I don't know how this got started in the "tuning world" but it is a no-no.

The crankcase vacuum created by the tube running from the PCV to the suction side of the engine (behind throttleblade) is REQUIRED for the piston rings to seal properly. This greatly (immensely) reduces blow-by and provides a tight combustion seal. Some studies have shown this to be the primary sealing method of the rings since most modern day engines use low-tension rings to reduce parasitic drag.

Also, since the MINI is a positive pressure engine, blow-by (air bypassing the piston ring seal) could pressurize the crankcase if the rate of air out of the atmospheric vent (that 10mm silicone hose) is less than the air going in. This will cause leaky seals, poor idle and light throttle driveability. It will also pump oil the other way, pushing oil past the rings and into the cylinder, causing combustion contamination.

Racers pay big bucks for specialized crankcase vacuum pumps to increase performance and reliability beyond the typical PCV system.

A oil catch can on the crankcase vacuum leg is used to strip the oil out of the air stream. The oil catch can on the valve breather side is to catch oil that may slosh into the tube from high g-forces, or overfilling, and not recirculate it into your incoming clean air supply."

Audi2ptzero

BTW the hose leading to my catch can for an audi is 1", so its much larger then the 10mm they talk about on the mini.

QGMika

uum?

WJM

for the mini the vac on the back side helps keep the seals biased (think of it like a wiper blade) which helps them not pass oil though

on a turbo car... it is about pressure deltas acress the seals... if you apply pressure to one side, and vac to another side then you basically are sucking oil through at a rate of P1 + P2
if you vent p2 to atmospher you lower the total pressure to P1.

given that most of us running catch can, have also raised the boost to 20+ psi... that's the reason

Gldnrkt(GT3076R)

umm..ya..what will said....lol

QGMika

well the mini is supercharged..and i dont really understand your explanation, could you elaborate?

WJM

situation 1.

Engine under vac...
thus negative pressure in the combustion chamber on the piston down stroke.

the check valve in the crankcase system opens and the backside of the piston sees vacuum from the intake manifold. This basically makes the pressure on one side of the piston the same as the other side.

the seals are essentially balanced and at a "zero" position

situation 2
Engine under boost... Positive pressure in the combustion chamber. How can you minimize the pressure behind the piston now? Well normally that is when the pcv opens and the air in the crankcase is sucked through the pcv valve, putting yet again a vac on the backside, allowing the piston to downstroke easily.

the seals under this situation get pressure on one side and vac on the other...this causes the seal to bias downwards from the zero position.

As you raise the boost level...this bias will become more extreme (more boost P1 + more vac P2 = total pressure on the seal Ptot=P1+P2)

If you add an oil catch can vented to atmosphere, you eliminate P2. So now all the seal sees in P1 while under boost.