Further to my last post on this one (thanks for the help!) I'm still having problems with this.

System is currently like this:

2.5ltr BMW straight 6

Aviaid 3 stage DS pump

2 gallon DS tank

Crankcase breather from cam cover to inlet manifold

2 x 12mm vent hoses from top of DS tank to breather tank - bottom of breather tank roughly level with top of DS tank.

Oil is coming out of the breather hoses at a serious rate of knots - currently looking at it in the work car park with a small river of oil running from under it. Not pretty. Tank less than half full - in fact, probably less than 1/3rd by now. This is happening at high engine speeds.

It has been suggested that it should be more like this;

Crankcase breather fitted with one way (out) valve, to allow crankcase vacuum to occur. (Alternatively routed to DS tank breaher, so that any air sucked in to the crankcase and thus out of the DS pump is exactly balanced out by what is sucked out of the DS tank)

1 x 19mm breather hose from DS tank to breather tank, to reduce air speed

Better DS tank with baffling around breather take offs.

Of this, what I can afford to do before Le Mans is:

crankcase breather to DS tank

19mm hose through DS tank cap to breather tank + one 12mm hose the same route - surely the lower the air speed the better!?

Any help much appreciated! (Especially if you come to my house in Manchester and fix it for me this evening while I drink beer in the sunshine and chant motivational catchphrases at you )

Dave

PS The other suggestion was that my piston rings are shafted and the engine is breathing. Can't afford for this to be true, so ignoring it. If there's any way I can test this though, please tell!

A compression test will give you an idea if the rings are shagged (hope not!). Is the crankcase breather blocked? If it is, oil will try to get out of every orifice - including the dipstick hole.
I was sold an engine which was 'breathing heavily' in need of a rebuild. That was a blocked breather pipe and the engine is still running 3 years later.

Dont think connecting your DS tank to the breather on the engine is a good idea, reckon you will end up with the crankcase fumes contaminating your oil.
Mac

The DS scavenge pump will suck a lot of the blow by gases from the crankcase into the oil tank anyway, some systems use no crankcase ventilation & rely on the above. I would suggest a cylinder leakdown test rather than a compression test which will show you where any compression leakage is.
Regds
Ian

My first thoughts is it is the design of the DS tank. This should seperate oil and air. The oil should drop to the bottom and the air to the top.

Thinking aloud...............why is oil pissing out of the breathers? Because there is higher pressure in the DS tank than the breather tank, (that is obvious because the pumps are pumping into the tank at twice the rate they pump out, so this should apply to all DS systems). Also there is oil at the top of the tank near the breathers. This must be happening because oil is going out of the breathers when it should just be air.

Also why does it happen at only high revs? Think what is different at high revs than low revs.....More oil is pumped and has to be controlled.

Try venting the crank case to atmosphere and see what happens.

On my DS system I vent the crank case into the top of the DS tank. the other goes to the overflow tank.......HOWEVER IT IS IMPORTANT WHICH ONE GOES TO WHICH I THINK. LOOK IN YOUR TANK AND CHECK HOW THE BREATHER OUTLETS ARE PLUMBED.. (mine is a Pace tank)

I hope you get it sorted and get to Le Mans.....one day i will go in my Minor.

John

Just a thought.........

try blocking off the cam cover breather pipe altogether, just have the dry sump tank vented to the breather tank. The 2 scavenge stages should shift enough air to keep up with the engine breathing, but if you have the camcover connected to the inlet manifold, at wide open throttle you'll lose inlet vacuum and the pump will never be able to generate any vacuum, it'll be pulling air in from the inlet manifold all the time meaning one hell of a lot of air going into the DS tank.