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  #11  
Old 28th December 2015
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I have looked at the tiny little poppet valves in the rocker box and I am telling you there are vent slots in the right side of the crankcase that allows the crankcase to pressurize the cam case and this forces pressure up the pushrod tubes into the head. This is PUMPING VOLUME so as the pistons fall on the power stroke pressure rises in the crankcase the cam case and the rocker boxes. The only way air gets in and out of the engine is through those two tiny breather bolts as the rest is sealed. The oil mist condenses in the rocker boxes which are VERY crudely cast and can get into the air cleaner as it runs around in the rocker box.
From what I under stand, this is totally normal and is designed to work that way, except the purpose of the stock umbrella valves is to separate oil from vapor and let only vapor get to the carb.

Quote:
The only way air gets in and out of the engine is through those two tiny breather bolts as the rest is sealed.
The umbrella valves, I assume are the same thing you are calling the poppet valves. I am saying their entire purpose is meant to minimize air flow in / out of the crank case, but leaving just enough air movement to push the oil around where it is supposed to go. But you keep saying air is pumped in and out, which is not entirely true, or at least misleading. If you take the one way valves out, a whole lot more air will be pumped in and out, but that is not how it is supposed to work.

This is a common complaint when the one way valves blow out, or with big displacement engines, leaking piston rings, or other problems, but with proper one way valves, stock displacement engines, and on rubber mount Evo's, it is not a common problem, and is easily fixable, usually replacing umbrella valves or adding external one way vent. Racing motors require a whole lot more to fix related problems. Street engines do not need racing engine solutions.
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Last edited by XLXR; 28th December 2015 at 07:47..
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  #12  
Old 28th December 2015
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I'd like to rig up a vacuum/pressure gauge to a properly maintained engine to see just what the pressures are. My guess is that the design is a few pounds of pressure on piston intake/power stroke and a slight vacuum on compression/exhaust stroke. Net average pressure maybe a pound over atmospheric... Just a guess. Anyone checked?
Joe
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  #13  
Old 28th December 2015
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It has been checked, but it changes so rapidly following piston movements, it is difficult to get a detailed reading of the up/down spikes without electronic measuring gizmos. Mechanical gauges are too slow for accurate results.
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Old 28th December 2015
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So, is the prevailing thought that I should just wait until I can do a cam chest vent?
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Old 28th December 2015
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having a positive pressure under the pistons are detrimental to performance. the obvious is wasted power having to move it around but the other thing, oil control can be affected. remember, the top ring is compression and the second is a dual purpose, aka, back up and scraper and the third oil control. if c/c pressure is high, oil will have a tendency to stagnate. if there is a negative pressure, the ring work better. most engines work well +3" > -5" and that is the way we setup commercial units. the positive pressure used in dirty environments.
big problem with case vent is oil control, taint any, you must use a catch can and lord help you if you live in cali. you will be issued a citation and a summons to fix it. the c/c vapors are not detrimental to performance unless you are a fuely, do not think they sell that at walmart. there are fixes.


20+k miles, no oily mess. stock umbrella's never changed, the cleaner mount and through bolts are modified and have larger flow area. all vapors are inline with air flow unlike the stock where the flow gets lazy and can drop out.
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Old 28th December 2015
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I understand how crankcase venting works. I also am of the opinion that I don't want it recirculated back to be ingested by the engine. My only question was if the holes in the stock vent bolts are big enough. You are arguing points that are not even close to the scope of the question.
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Old 28th December 2015
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Quote:
Originally Posted by nicksta43 View Post
I understand how crankcase venting works. I also am of the opinion that I don't want it recirculated back to be ingested by the engine. My only question was if the holes in the stock vent bolts are big enough. You are arguing points that are not even close to the scope of the question.
The word "stock" should be anugh of an answer,
the Mo-Co knows more about this engines than you would ever imagine.

The only time the small holes are restrictive, is on the very first down-stroke after a start up,

after that the umbrella check-valves prevent any high c-c presures,
as long as everything is in working order.


Tore


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Old 28th December 2015
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However I am planning on modifying part of the stock system. Changing the perimeters, those tiny holes work well with vacuum, but my question is do they still work well without that vacuum assist?

That's all I want to know.
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Old 28th December 2015
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Originally Posted by nicksta43 View Post
However I am planning on modifying part of the stock system. Changing the perimeters, those tiny holes work well with vacuum, but my question is do they still work well without that vacuum assist?

That's all I want to know.
There's negligible vacuum present on the atmosphere side of the throttle plate, which is where those breather fittings dump into.
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Old 28th December 2015
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Quote:
Originally Posted by nicksta43 View Post
However I am planning on modifying part of the stock system. Changing the perimeters, those tiny holes work well with vacuum, but my question is do they still work well without that vacuum assist?

That's all I want to know.
Those small holes are to prevent the low pressure inside the air-filter from sucking oil out of the engine,
so if you are going to vent into atmospfere, making them bigger will not hurt, but I bet it will neither help anything.

By "without vacum assist" I hope you don't meen getting rid of the umbrella valves, they are crucial to a working c-c ventilating system.

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