case and head vents, do I need to run a breather box? Options

[wayne1234]

Ok dual webber carbed 2.0, I think the PO had the head vents running to a T then to the oil breather near the oil cap... Is this right?? I did a search and now I'm really confused,,,,

[HAM Inc]

Good work Jake! But I can't but help wonder. Can you be more specific about the sort of computor you used. How can we be sure that Google didn't just make up these results. They surely have an agenda, everyone else does!

I have to admit that I have been sucked into this goofy discussion now and as a result I have to respond to Murray's assertion that cam loading doesn't change with speed.

Here's what I said:

The cam loading at speed is nothing like what it is at assembly. At near redline speeds the load on the cam at max lift (as the lifter goes over the nose of the lobe) may be 5 lb's it may be near 0. At speed the greatest load that the cam sees is when the lobe encounters the stationary valve train and has to get it moving...and in a hurry.

Here's Murray's response:

AND if you can be believed apparently a compressed valve spring has 5-to 0 ft lbs of torque at full compressed height.(valve fully open)(on the nose of the cam).... surely this too was a typo error...(seems like you guys are just digging your hole deeper). who knowes maybe you enjoy self induced flagulation.....Murray..

You missed the point Murray. Ofcourse I know that springs are displacement sensitive. Meaning a spring with a rate of 250lbs/inch will require 125lbs to compress it a .5". What varies with engine speed is waht is actually compressing the spring.

Let's consider an engine that is properly sprung to control the valves at 7000RPM's. When the engine is turning 7000rpm's the greatest load on the cam (notice I said the greatest load on the CAM) occurs when the lobe comes around and encounters the stationary valve train, which it has to get moving in a big hurry. Once the mass is moving inertia plays an increasing role over the course of the lift event. The more inertia the less the cam load.
Eventually as the mass approaches peak lift the load on the cam may be reduced to only a few pound. This is why we can draw no meaningful valve train information from turning an engine over with a torque wrench.
Other factors include the stiffness of the pushrod. If the pushrod is not stiff enough it will bow when the lobe comes around and encounters the stationary valve train. This bowing delays the opening of the valve and stores energy in the pushrod, to be released later in the lift cycle. As inertia takes over and the load transferred through the pushrod to the cam decrreases the pushrod unloads its energy and actually pole vaults the valve contributing to valve float. Did you catch all of that, Mayor?

Now, here's a question that hasn't been broached at all yet in this discussion that could be fun and interesting to the community. Why do we need to vent the crankcase at all, and why do some configurations require more venting than others?. The answer varies by application and engine specifications and is a lot more complex than it appears on the surface.
Mayor perhaps you would like to weigh in on this.