Carried over from the Valve cover baffle design thread. Dave brought up something I thought may be interesting.







That's certainly not dumb. I don't think airflow through the engine has been discussed in detail. It may not be an area that needs improvement. Slightly more modern engines, such as the 305 in my Firebird, don't appear to have any kind of baffling to direct air flow in any particular way. I'm interested in hearing about it if there is anything important to know.



One thing, if your observations indicate that it's blowing up through the timing cover and into the valley, it must be drawing air from somewhere. The only source I can think of is through the distributor hole. I will guess that the hot crankcase gasses rise to the top of the engine where they can be drawn out and the cooler air will make its way to the crankcase. I guess that would be convection.



There have been at least 3 different arrangements for crankcase evacuation. It will be interesting, if not pointless, to know how they actually compare. My shop manual has a diagram showing how it should flow for the trucks original setup. I'll dig that out.


Lawrenceville, GA

The two vent holes in the timing cover area and the larger hole at the back and around the distributor gear do help to vent any excess pressure generated by piston ring leakage back to the top of the engine. This pressure is obviously not near as much of an issue in an engine with a good ring seal as opposed to a worn engine where the rings are permitting some of the combustion pressures back into the crankcase and creating ‘blowby’. This generated pressure is also hotter than normal thus raising internal crankcase temperatures and in turn promotes the baking of oil residues to internal surfaces. The additional air being generated in the crankcase as a result of ring seal and/or the churning of air in general by the up and down movement of the pistons becomes evident when running an engine on the dyno with a lexan (clear) valley cover in place.

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Simple design theory says to keep air flow restricted to the top of the engine where engine heat will bring to the top any unwanted residuals such as moisture. Cool air also needs to be kept from the hotter regions of an engine if for no other reason than minimizing condensation. The ideal situation on a V8 is a positive crankcase ventilation system where fresh air goes in at the front of one valve cover and out the rear of the cover on the opposite side. Making any system more complicated than this simply adds more variables and potentially introducing more undesirable outcomes into any scenario. Giving it just a bit more thought says any added air flow to the lower areas of the engine will create a situation where additional oil particles will be carried to the top and out thru a PCV or crankcase evacuation system instead of the oil remaining at the bottom of the where it ideally needs to stay if in suspension. Keeping any fresh air inputs as far away from the oil sump also extends the life of the oil by minimizing or at least slowing down oxidation that occurs when large surfaces areas of oil is exposed to oxygen.

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On the race engines, I prefer to maintain a slight vacuum on the crankcase in which to minimize the movement of air that’s created by the movement of the pistons. In this environment, the air itself creates an additional drag on the engine.

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Here is a past thread regarding additional holes in the lifter valley.

Drilling additional holes for oiling and/or venting

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As always, just food for thought.

Lorena, Texas (South of Waco)