T.O.O. Valve Cover Breathers

Posted by alloy_625 on May 05, 1998 at 20:10:13:

You've been talking about the slash cut tubes for the crankcase breather on Hondas and I noticed that Toyota on the 3S-GTE (Celica & MR2 turbo engine) uses a slash cut tube, BUT the angled face is facing the compressor and not the airbox leading me to wonder if it should be turned the other way so that the crankcase gets pressurized.. There is a problem with oil getting into the intake tract and I'm wondering if the significant airflow on boost is sufficient to start sucking air/oil out of the head.


Re: T.O.O. Valve Cover Breathers


Posted by T.O.O. on May 06, 1998 at 18:53:46:
In Reply to: T.O.O. Valve Cover Breathers posted by body on May 05, 1998 at 20:10:13:

While I'm not an expert on all (or any) foreign engines, I can tell you some things about air flow and fluid dynamics.
With the slash facing the out going air, it will indeed suck on the tube. A good example of this use is the tubes you frequently see welded into the collectors on normally aspirated "comp." eliminator drag cars. The tubes extend into the collector and the exhaust rushing past creates a vacume. These tubes normally lead to some Chrysler oriented "breathers" on each valve cover, and they do a very good job of creating negative crankcase pressures, allowing engine builders to use low tension rings, gas ported rings, and many other friction saving devices which are normally busy containing oil.
If the end of the tube is flush, or perpendicular to the flow, regardless of the amount of intrusion into the tube, it will still suck.
The only way to insure positive head pressure is to use a forward facing slash cut tube, or a tube bent to a right angle and the opening facing the on coming flow. These tubes would ideally "like" to be placed on the short side of the curve in the induction tube, as that's where the highest flow velocities will be. Remember: Regardless of application, if you want to "eye-ball" something to determine flow efficiency, the flow (bulk and highest velocities) will always seek the shortest path from entry to outlet.
I have seen many JR superchargers installed with the simple brass fitting screwed into the intake wall, placing the end of the fitting flush with the inner surface of the tube, and every one has had oil in the tube originating at the fitting. This is not a desirable condition. Honda didn't design the slash tube and place it on the inside radius of the intake tube just ahead of the throttle body for nothing..they wanted to place positive pressure on the upper part of the engine to force the oil vapors to travel through the canaster to the pcv valve.
If a factory Toyota has the tubes slash cut and not facing the flow, they're certainly enviting oil vapor to be sucked from the top of the engine, and sinse there's no metering valve, I'd have to say that you should ask the folks at TRD about "why", because I'm not here to argue with the "factory", and they obviously did it that way for some reason....................................T.O.O. ................................