Thread: Crankcase Breather Options

Originally Posted by 110Landy86

I have teed the 8 mm outlet from the cover to the intake preturbo

The turbo specialist the that did my set up ran a line from the rocker cover to pre turbo. Ben's right a Mahn filter In between will extend the life of the turbo.

Originally Posted by mark2

Is it correct that on an NA engine, the tappet breather is actually a filtered air inlet, which allows flow through the crackcase via the road draft outlet? My engine appears to have some sort of valve or restrictor at the intake fitting which only allows one way flow from the intake ie into the tappet cover.

Regarding the open draft tube, is there any reason to worry about dust entering the crankcase via here? What about deep water?

As far as dust goes not a problem deep water shouldn't be a problem as long the engine is running I have a port on my snorkel and can hook up my syphon hose if I thought it was needed


AM

All fixed, thanks for the info guys☺

Resurrecting this thread somewhat....

When fitting my turbo, I plumbed the vents as many others appear to have done, as follows:
-8mm rocker breather to just before turbo inlet
-large crankcase vent to relocated oil separator and road draft tube
-inlet manifold connection to boost gauge

I've noticed that there is now no oil dripping from the road draft tube, as it used to do when n/a. The outlet tube which vents to atmosphere is clean. This seems unusual as the turbo is only going to increase blow-by. There is a fair amount of oil at the turbo inlet which can only have come from the rocker breather.

My conclusion: a partial vacuum is being created at the turbo inlet (I can pop the restriction indicator on a hard pull with the safety element fitted) which is drawing crankcase gases through the rocker breather into the turbo inlet.

So what? - you're probably thinking. As I see, it this means that the vacuum at the rocker breather is potentially causing unfiltered air to be drawn into the crankcase via the road draft tube (doesn't seem like a good thing). Air is essentially flowing in the reverse direction through the large open tube.

As I mentioned in an earlier post, I believe the fitting on the n/a inlet manifold is for the purpose of providing a filtered air inlet to the rocker cover to assist gas flow through the crankcase and allow blowby gases to exit via the road draft tube. Common thinking appears to be that the 8mm hose on the rocker is an alternate point of gas exit to the side fitting on the block, but I don't think this is the case for a n/a engine. The very small restrictor in the manifold fitting supports this idea, which provides a filtered air inlet without creating a venturi effect. Old road draft systems often had a wire screen inlet breather in the filler cap.

The immediate question now is what to do with the 8mm hose between the rocker fitting and the turbo inlet. I can see 4 options:

1. remove the hose and block both the rocker fitting and the turbo inlet fitting
2. fit a check valve to allow filtered air to flow into the rocker cover - one way flow should prevent oil and vapour entering the turbo.
3. block the turbo inlet fitting and fit a small filter (eg fuel filter, sintered metal fitting etc) to the 8mm rocker hose which will allow filtered air to enter the crankcase and blowby to exit via the road draft tube.
4. put the hose back in the original configuration ie between the inlet manifold and the rocker and block the turbo inlet fitting. I know that in theory this will pressurise the crankcase under boost, however the restrictor at the inlet manifold fitting is about 0.5mm in diameter, which is tiny compared with the 32mm diameter of the block vent. The flow at 20 psi through such a small restrictor surely wouldn't pressurise the crankcase when it can vent through the much larger block fitting.

The more I think about it, I lean toward option 4......
Thoughts welcome please.

Originally Posted by mark2

My conclusion: a partial vacuum is being created at the turbo inlet (I can pop the restriction indicator on a hard pull with the safety element fitted) which is drawing crankcase gases through the rocker breather into the turbo inlet.

So what? - you're probably thinking. As I see, it this means that the vacuum at the rocker breather is potentially causing unfiltered air to be drawn into the crankcase via the road draft tube (doesn't seem like a good thing). Air is essentially flowing in the reverse direction through the large open tube.

Agree this is possible. I think Dougal may have somewhat proven this by sucking sump oil into his turbo.

Originally Posted by mark2

As I mentioned in an earlier post, I believe the fitting on the n/a inlet manifold is for the purpose of providing a filtered air inlet to the rocker cover to assist gas flow through the crankcase and allow blowby gases to exit via the road draft tube. Common thinking appears to be that the 8mm hose on the rocker is an alternate point of gas exit to the side fitting on the block, but I don't think this is the case for a n/a engine. The very small restrictor in the manifold fitting supports this idea, which provides a filtered air inlet without creating a venturi effect. Old road draft systems often had a wire screen inlet breather in the filler cap.

Disagree. My understanding is the crank case will be positive pressure from blow-by, especially if you have a turbo. The turbo inlet will be negative pressure. If you connect these together, flow direction can only be from positive to negative.


In short, I propose you buy a Provent with a check valve for oil return.

My crank case and rocker cover both vent to a Provent.