I have a 270 hp. solid lifter engine. It has a vented crankcase breather cap on it now. The original non - vented cap was in the parts box that came with the car. The intake manifold is covered with oil from the vented cap. If I change it back to non-vented will I have sufficient ventilation? This car is set-up as RPO 246 , but the rubber hose is NOT connected to the back of the carb. At the back of the intake is an elbow with a pcv and rubber hose with corbin clamps.Not a conventional road draft tube. Looking for suggestions.
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Re: 61 crankcase breather cap, vented vs non-vente
I am no authority, but on my 61', it has the vent tube going to the base of the carb, and a vented oil filler cap. I have never had any oil on the manifold, and the engine seems to be properly vent of fumes. There is a PCV valve in the line going from the crankcase vent tube opening, to the carb base...... -
Re: 61 crankcase breather cap, vented vs non-vente
I am no authority, but on my 61', it has the vent tube going to the base of the carb, and a vented oil filler cap. I have never had any oil on the manifold, and the engine seems to be properly vent of fumes. There is a PCV valve in the line going from the crankcase vent tube opening, to the carb base......Comment
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Re: 61 crankcase breather cap, vented vs non-vente
Peter -
The vented oil fill cap is the "intake" for the crankcase vent system, and the "exhaust" is the hose/tube into the base of the carb, where the crankcase vapors are sucked into the intake and burned. If you are showing oil vapor residue around the vented fill cap, I'd look for either a clogged PCV valve (if your setup has one) or a blockage in the hose/tube to the carb, either of which will turn the vented fill cap into the "exhaust" instead of the "intake" for crankcase ventilation. It's a circulating system, and if the carb end is blocked, crankcase pressure will blow the vapors out the "intake".Comment
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Re: 61 crankcase breather cap, vented vs non-vente
Peter -
The vented oil fill cap is the "intake" for the crankcase vent system, and the "exhaust" is the hose/tube into the base of the carb, where the crankcase vapors are sucked into the intake and burned. If you are showing oil vapor residue around the vented fill cap, I'd look for either a clogged PCV valve (if your setup has one) or a blockage in the hose/tube to the carb, either of which will turn the vented fill cap into the "exhaust" instead of the "intake" for crankcase ventilation. It's a circulating system, and if the carb end is blocked, crankcase pressure will blow the vapors out the "intake".Comment
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Re: Been wondering about this myself???
Barry -
I'd save the closed cap for the judging field and run the vented cap for normal driving as you've been doing. The closed cap was used only on solid-lifter 2x4's and F.I.'s "to reduce oil pullover at high rpm when used under racing conditions" (read high crankcase pressures due to heavy load/high-rpm causing both the oil fill cap and the road draft tube to be "exhausts" for oil vapors). Hydraulic-lifter engines used the vented cap, as they weren't expected to be used "under racing conditions", which kept crankcase pressures down so the vented fill cap/road draft tube vent system (crude as it was) would function as long as the car was moving, which generated a low-pressure area at the end of the road draft tube). I use the vented cap on my '57 270, with not a hint of oil residue anywhere 5,000 miles after rebuilding it, and keep the "closed" cap in a bag on the wall for judging, along with the original gas cap and radiator cap.Comment
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Re: Been wondering about this myself???
Barry -
I'd save the closed cap for the judging field and run the vented cap for normal driving as you've been doing. The closed cap was used only on solid-lifter 2x4's and F.I.'s "to reduce oil pullover at high rpm when used under racing conditions" (read high crankcase pressures due to heavy load/high-rpm causing both the oil fill cap and the road draft tube to be "exhausts" for oil vapors). Hydraulic-lifter engines used the vented cap, as they weren't expected to be used "under racing conditions", which kept crankcase pressures down so the vented fill cap/road draft tube vent system (crude as it was) would function as long as the car was moving, which generated a low-pressure area at the end of the road draft tube). I use the vented cap on my '57 270, with not a hint of oil residue anywhere 5,000 miles after rebuilding it, and keep the "closed" cap in a bag on the wall for judging, along with the original gas cap and radiator cap.Comment
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Re: correction RPO 242 not 246!!
I will test my PCV valve and connect the tube to the back of the carb as per RPO 242. This should create a vacuum that will draw air in the vent cap and not discharge oil. I'm getting tired of wiping oil off the intake. I like the idea of using the non-vented cap for judging only. Thanks for your suggestions, PeterComment
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Re: correction RPO 242 not 246!!
I will test my PCV valve and connect the tube to the back of the carb as per RPO 242. This should create a vacuum that will draw air in the vent cap and not discharge oil. I'm getting tired of wiping oil off the intake. I like the idea of using the non-vented cap for judging only. Thanks for your suggestions, PeterComment
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