Crankcase ventilation question

[andrew_mx83]

Hi Techheads

I'm making new cam covers for my 7m and would like to avoid having hoses and shit coming out of them unnecessarily.
The factory setup has a 1" breather hose coming from a high point in the block, which goes into one cam cover at the front. Once inside the cam cover the gas is able to move around inside the oily area of the head, and exits via a 10mm baffled fitting at the rear of each cover.

It is my understanding that the PCV system is solely venting crankcase pressure, as a result of blowby. I cant really see any gasses leaking past the valve guides and VSS to generate any significant pressure in the head.



So my question is, does the gas really need to be bought upto the head by this 1" hose before it exits the engine (to intake manifold/catchcan etc), or can i add baffling at the outlet on the block and extract the gasses there instead?
Being a belt driven engine there is no large cavity for a timing chain and aside from the oil drains, the head and block of the 7m dont really share the same "atmosphere"

[cambelt]

Andrew the answer is yes , the early m,s and 2 m,s had the breather on the passenger side of the block on that machined area above the engine mount , it was a 1 inch pipe that went downwards .
Dave

[andrew_mx83]

Awesome, thanks Dave

[SHEPPO3930]

the 4age doesn't have an external "gas pipe" it only has the oil return passage down the exhaust side of the block (between cyls 2 & 3). all the crank pressure vents up into the head via this passage, then up and out through the cam covers. since 4age's don't have issues when boosted, maybe there's hope for your 7M? might be worth a look?

[andrew_mx83]

hi sheppo i was under the impression that 4a's DID have breathing issues when boosted?

i was actually chatting about this idea with a mate who plays 4a's and we discussed the idea of adding a vent in the block or sump to vent the blowby gasses straight from the crankcase rather than it having to travel up through that oil drain from the head.... which really doesnt seem like the greatest solution when you think about it, cant be much room left for the gas with all that oil draining down.
i think the 7m's external hose is a much better way to do it. but then i ask why you need this hose to take it up into the cam covers at all? why not just deal with the gasses straight out of the crankcase?

[dnegative]

4AGZE's run fine on 12psi with the stock breather, my half shagged motor ran sweet with decent blowby and 8200rpm so the stock PCV setup seems to work fairly well.

Does the hose double as an oil drain?

[SHEPPO3930]

Maybe look at a PCV on the hose from the block so under vacuum u don't draw crap in from the catch can? When people fit catch cans to EJ20ET's there's usually a pipe straight from the bottom end to the catch can, along with a pipe from each head.

I've played with 4age turbos a bit and not noticed any major breathing problems up to 19-20psi boost pressure. But someone with more experience might have some additional info.

[andrew_mx83]

Ok, thought i had read somewhere about people fitting 2 intake cam covers for better breathing or something?

good to hear that the soobies take a pipe from the block to the catch can.

i dont think the hose acts as an oil drain, its way too high up. the oil level would have to be half an inch above the cam cover gasket line and i think you would have other issues by then...

[andrew_mx83]

oh yeah will have a look at a PCV valve as well, but im not sure that the crankcase would ever see vacuum in a wet sump application, unless you were breathing the vapours back into the inlet manifold (and who does that?)

[bermy]

oh yeah will have a look at a PCV valve as well, but im not sure that the crankcase would ever see vacuum in a wet sump application, unless you were breathing the vapours back into the inlet manifold (and who does that?)

If you care about oil consumption, you should. The purpose of the catch can is to keep the vapor from entering the manifold while still using manifold pressure to lower the crankcase pressure. True that in a wetsumped engine it'll only create partial vaccum under low load/low throttle position, but it helps the rings seal better, helps oil from going past the rings and helps the seals and gaskets to keep oil inside the engine. If you simply vent the gas outside, blowby gas will create positive pressure inside (depending on how your rings are sealing) and it will actually do the opposite, force oil to go to the lowerpressure zone, past the rings and past the seals and gasket. Partial vaccum inside the crankcase also helps the efficiency of the engine by lowering air resistance of the rotating assembly. The tip of the counterweights on a 4A-GE crankshaft travel at over 200km/h @ 9000rpm... get your hand out the window in a car travelling at that speed and you'll appreciate how much resistance that it. Truth on a wetsumped 4A-GE by the time the engine hits those RPM level crankcase pressure will probably be around atmospheric pressure but at lower speed and load it will help fuel economy and performance