Breather Concepts, ...taking one from Jake Options

[yeahmag]

I'm considering blocking off my head vents and running a -10 or -12 breather solely from the oil filler/breather to a Morosso breather tank (or the like). The idea here is to keep the crankcase at a lower pressure than the heads so the oil tends to move from high pressure to low (aka from the heads to the case).

Anyone else doing this yet? If so any comments or pictures?

Thanks!

[HAM Inc]

BTDT. A single -12 line from the chimney is all we ran on our F-Prod car. The oil will return more quickly from the heads to the crankcase with no head vents.

This was a hot topic here on World a year or so ago. I was amazed at how many people got down-right hostile at the suggestion that head vents were not only unnecessary but counterproductive.

The drain back slots on a type 4 are restrictive. If the heads are vented the crankcase pressure interferes with the oil draining back from the heads. Close off the head vents and the pressure differential between the rocker chambers and the crankcase goes away allowing the oil to flow through the narrow slots without interference from crankcase pressure.

[ChrisFoley]

...
The drain back slots on a type 4 are restrictive. If the heads are vented the crankcase pressure interferes with the oil draining back from the heads. Close off the head vents and the pressure differential between the rocker chambers and the crankcase goes away allowing the oil to flow through the narrow slots without interference from crankcase pressure.

The drainback slots on a type 4 crankcase aren't narrow, nor are they restrictive.
Their cross-section is at least as large as the cross-section inside a pushrod tube,
and they're shaped in a manner that ensures adequate flow without any likelihood of becoming hydro-locked.

Crankcase pressures are unlikely to ever be above 1.01 atm., vented or unvented.
It doesn't take much of an opening to bleed off that pressure. The diameter of the opening affects velocity of flow far more than volume.
Those very low pressures have little to do with preventing oil from draining back from the heads.

A venting system ensures equal pressure in the 3 chambers of the engine when they're all connected to a central cannister that's open to the atmosphere.
No differential will exist.
On the other hand, when only the crankcase is vented, there will certainly be a pressure differential due to the constant supply of oil into the rocker boxes.

Anecdotal evidence to the contrary (factory design changes, etc.) notwithstanding, there's no proof that unvented heads are beneficial to oil control in comparison to a well designed breather system on a carbureted T4 engine.

BTW, the cross-section of three -8 hoses is greater than the cross-section of one -12 hose.