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Old 08-27-2002, 08:42 PM
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Post crankcase ventalation system

Chevy used to make a vent system that was plumbed from the valve covers to the exhaust header. At the header their was a one way check valve. I think , the theroy was convergent/divergent. It was souposed to draw out vapors and expell them out the exhaust. I bring this up , because as a kid , i allways eliminated this system as being junk. I see where Summit sells this system as a add on kit. I was wondering what you guys think . Did and does it work?
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Old 08-27-2002, 09:14 PM
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This system is standard practice on drag cars where a vacuum pump is not used. It evacuates the cranckcase of pressure by way of the header, when the crankcase has a vacuum put on it it seals up the rings better for more power, and also it keeps the oil from blowing all over the valve covers, or so I think.
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Old 08-27-2002, 09:18 PM
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Works very well on race cars, not so well on street cars in my opinion. The problem is the check valve needs some sort of backpressure to open (with muffled exhausts) and this means a pressurized crankcase. Open header race cars do not have any backpressure usually and the system works best in that fashion. PCV is the best for the street to me anyway.
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Old 08-28-2002, 01:45 PM
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So ,then, i pose the question, what about the high flowing large exhuast systems being used today. They decrease back pressure don`t they? I understand your thinking the back pressure would force pressure into the crankcase.(If the oneway valve were to fail) However , it would seem to me the one way valve, in combination with the large size, full flowing exhaust systems(Flowmaster,etc,)would allow this system to work like it would on a set of open headers.(similar)And indeed if it decreases crankcase pressure, it would seal better as well.Less oil leaks , better ecconmey, performance,etc. I really want to work this out in my mind. You see when i take the 57 chev p.u. down for the camaro clip install , i want to change a lot of things. Rewire the truck, move the gas tank, lower the stance all the way around the truck. I`m doing my home work in advance.I have a 4 bolt 350 to build and i want to do it to near perfextion. (Dream) Motor. My dream motor i`m sure is not what some of you would choose.
I want to build a balanced , 350, that is near stock.(run on regular) I have 202 cast iron heads to use, and want to do everything i can to get gas mileage out of it. The 57 chev p.u. weighs a bunch. Any way that is why i am intrested in the evacuation system! Any other ecconmey ideas out there? I have burnt up 2 700-r4 transmissions, they were great for gas mileage. 1600rpms at 65 was too cool!! But they could not stand up to the built 350 in the truck now. Or rather to all the burn outs~!!!!!Thanks guys
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Old 08-28-2002, 02:14 PM
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slider, come on! just stick your stinkin pvc valve in your valve cover hole LIKE YOUR SPOZED TO, (that would be the rear of the pass. side) run a hose like 4 inches long to the bottom of your air cleaner and FUHGETTABOUTTIT BRAHHDAAH!!!! <img src="graemlins/nono.gif" border="0" alt="[nono]" />
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Old 08-28-2002, 02:32 PM
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The problem Slider is that street cars have low flowing exhaust volumes at typical speeds encountered on the street. These systems work on a venturi principal and depend on volume flow to extract crankcase gases. Without this volume the backflow valve closes and the crankcase must then pressurize to overcome exhaust system pressure, however little this is (&lt;1 psi typically with large exhaust systems). With a race car that never idles and has absolutely zero backpressure you can actually draw a vacuum on the crankcase and increase power, street cars will rarely reach this mode until highway speed. I think a combination system would be ideal but I have never attempted to construct one, shouldn't be too hard just use both systems on one vehicle.

Hmmmm...note to self...invent the perfect crankcase breather system and make millions. :p
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Old 08-28-2002, 04:58 PM
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Now it makes sense to me!!! Light bulb!!!Now i know why i threw them away as a kid!!! Gee thanks! So what about x stye or equalizer type exhaust sysetems then? Are they of any use? The principle of scavenging worth the effort?orthe cost?
Slider in Wa.
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