50 replies to this topic

[TerrA LX]

From what i read im best of having a sealed system from both rockers to a tank then plumbed back to the mainfold. That way ill reduce the amount going into the manifold from my current setup and it will keep the greenies happier.

If you run it this way with no PCV valve you will have to re jet your carburetor and possibbly change the power valve to compensate for the extra un metered air flow to the motor.

Edited by ALX76, 18 June 2009 - 11:59 PM.

[ls2lxhatch]

Thats pretty much why the factory system vents into the air cleaner, when the revs go up and the manifold vacuum goes down the PCV valve closes off, the pressure from the crank case has to go somewhere.

The PCV opens when vacuum drops and closes as vacuum increases. The design of the Torana PCV valve is different to the one explained in the following article however the principals are the same.

Engine Breathing Systems

To avoid upsetting the fuel/air mixture, the PCV valve must regulate the evacuation of these blow-by gases and vapours (which will be minimal at idling speed but will intensify as engine speed is increased). Since manifold vacuum is highest at low engine speeds, the PCV plunger will be drawn forward to a position that will restrict crankcase ventilation to a minimum thus ensuring no unsettlement of the air/fuel mixture. As engine speeds are increased the manifold vacuum will drop thus reducing the �pull� on the plunger which will slide back to a midway position allowing a greater flow rate from the crankcase. Since the engine demands more air/fuel mixture at high engine speeds, the escalation of crankcase vapours into the combustion chambers should not affect performance.

[TerrA LX]

Thanx for clearing that up Ls2.

[ls2lxhatch]

ALX76 you are correct in saying that the system will vent through the air cleaner if crankcase pressure builds up due to insufficient venting via PCV. This will happen at higher revs with low manifold pressure in a stock engine.

I guess that explains the size of the breather tubes on A9X's engine.

[Evan]

ok , im a tad confused here.
I have a mild 355 used for %50 street use and %50 track use.
What system should i be using? Running VN heads and rocker covers, i was going to run one hose from a rocker cover with a PCV to the carb and the other side to a vented catch can.

The way i look at it, this is no different from the standard system , but instead of venting to the air cleaner, venting to the catch can.

Does that sound ok , or should i be running somthing different?

Evan.

[ls2lxhatch]

Let me start be saying I do not have any race engine or car building experience.

Every 308 based track engine I have seen has larger breather tubes connected to either the middle or front of both rocker covers and a catch can as per the above photo. I have not seen manifold vacuum and PCV valve incorporated in a race track breather system.

It is obvious that race engine builders do not consider the stock breather tube diameter or location adequate for track use. Unfortunately the race breather system is in many cases not legal and does nothing to reduce oil contamination.

For a car that is used for both street and the track, I think you have three options.

1. Run a race breather system with catch can and larger relocated breather tubes, change the oil more frequently and hope you do not get defected.
2. Run the stock breather system and hope that you do not suffer excessive crankcase pressure, power loss, oil loss and seal damage.
3. Run both systems, block off the race system when on the street and the street system when on the track.

[Tiny]

Can i also ask,
What contaminants go into the oil from that get breathed out?

I'm considering to make mine legal, Making a tube around the outside of the filter on top of the breather to suck back the oily vapor that comes out of the filter to make the air in the cabin better to breathe!
The catch can still catches the oily watery mess that comes out the breathers though

Very interesting thread! Thanks!

[TerrA LX]

You can run the (for want of a better word) factory system, even with bigger hoses if you want, all you have to do is filter the oily fumes entering the motor, whther it be a catch can or whatever it must be sealed from the air filter right thru to the manifold inlet. ie so the only escape route for fumes etc is into the motor.
Race cars do not run this type of setup because you are ommitting un metered air into the manifold.
The factory has compensdated for this in their selection/design of carburettor.

[TerrA LX]

Just remember with these systems you are not only seperating oil and air, you are also seperating contaminants ie H2O.
Keep that in mind for your drain back setup.

[TerrA LX]

2, Non standard cams usually won't work well with PCVs; the reduction in manifold vacuum confuses the valve and it is often open when it shouldn't be having the same effect as an intermittent vacuum leak. For these applications simply replacing the PCV with a small fixed restrictor works. Tune to suit the orifice size.

I have never had or build a motor with a big enough cam to warrent this but excellent point.

[Stedz_lc]

I also run a catch can, I must admit it does blow a fair bit of smoke when it hasn't been driven for awhile or if its done a few short trips but after half hour or so it clears up, thou 11:1 doesnt help this, i get the same thin as nurvus a small oil stain on the bonnet, not drippin or anything. Ive also found after a hard time ie at eastetnats etc i drain my catch can and its a bit creamy/watery (not a head gasket) i think thats just the moisture and hot oil, i also think thats wats burnin off when i havn't driven it for awhile. I have not had a problem with this setup!!! I did have just K&N breathers in the rocker cover's and all that did was make a mess in the engine bay!!
Cheer
Ed.

[TerrA LX]

I also run a catch can, I must admit it does blow a fair bit of smoke when it hasn't been driven for awhile or if its done a few short trips but after half hour or so it clears up,
Ed.

Oil mist and/or steam?

Oil must be pretty hot to smoke.

Edited by ALX76, 21 June 2009 - 06:02 PM.

[Stedz_lc]

blow by!