Crankcase Evacuation System

[skyshadow07]

I know this seems like an old timer mod but it worked and works. So how come no one uses the system anymore?

If you have never heard of this before, it's a system that is much like a catch can but after entering the catch can, there is a line out of the can that goes to a check valve. The check valve enters the exhaust at a 45 degree angle to cause a suction effect. The suction effect pulls on the crank pressure to reduce the pressure. Reducing this pressure can help make power and reduce blow-by

 

[RonPorter]

IIRC it was Smoky Yunick, many years ago, that came up with a system like that to create a negative pressure in the crankcase. I think he used a small pump, though.

 

[Majestic]

The catch can on our SVO vents back into the turbo inlet line. Keeps the can from accumulating too much. No idea if that's an ideal situation, but we get a lot less smoke from the can and it's been running that way for a year with no problems that I have noticed.

 

[SM105K]

IIRC it was Smoky Yunick, many years ago, that came up with a system like that to create a negative pressure in the crankcase. I think he used a small pump, though.

That is why a lot of the fast drag race guys use a vacuum pump set up to evacuate the crankcase under extreme boost.

I watch a younger guy on Youtube with the channel "itsjusta6". They have a very loose boost set up mod engine in his Twin Turbo GT350. The engine is built for big boost and the rings are gapped for 30 psi. However they are still working out the boost controller bugs, and turning up the boost. At the point of the last video they are only seeing 20 psi of boost into the engine right now. Since the rings aren't expanding to tolerance yet, they are having crankcase pressure issues. In the last pass, the engine yeeted the engine oil plug, threads and all. It will be interesting to see how they remedy this issue.

 

[luigisho]

In the last pass, the engine yeeted the engine oil plug, threads and all. It will be interesting to see how they remedy this issue.

I'll be checking this out.

 

[SM105K]

I'll be checking this out.

Here you go.

 

[skyshadow07]

Well hold on guys, don't want this convo to grow incorrectly. I'm speaking about an old school system where the outlet goes to the exhaust. This means boost in the intake would not effect it, it is attached to the exhaust, past the turbos. Our current (OEM and aftermarket) systems all pipe into the intake side, that's how ALL PCV systems vent in modern cars.

 

[robert francis]

Back in the 1950's, many auto engines had what was a called a "road draft tube" used to vent the crankcase to the outside air. Usually it was a metal tube attached to either the side plate of a in-line engine or the valley cover of a V8 engine, and the tube ran underneath the engine into the open air stream under the engine. The way it worked was that back then, engine crankcases were open vented to the atmosphere by crankcases "breathers," usually some kind of metal mesh screen inside a cap, located on top of the valve covers. When idling , the crankcase was under a positive pressure and just "vented" crankcase vapors out these "breathers" into the atmosphere. But when the vehicle was in motion - there was a low pressure area at the "draft tube" opening and this low pressure area would then "draw" fresh air through the "breathers" on the valve covers down into the crankcase, and the crankcase vapors would now exit out the road draft tube into the atmosphere.

How really "effective" this system was, I don't know. But I can tell you that every highway I drove on the 50's and 60's had "black streak" in the center of the lane in the road.