With so little going on today I was thinking last night about a question that came up. Two of my cars have PCV values on one value cover and a oil fill breather on the other. New cars have an oil fill cap that is not a breather cap sealing the crank case breathing system. Is it proper to have a breather cap on an engine a PCV value?
On an older V8 the PCV valve was on one side of the engine and there was a breather cap on the other. A modern engine is not set up like one of our engines. no reason to make the comparison, we do what works for us. On a car with the front fill like a GM I don't like a PCV valve and a breather on the filler. I prefer my PVC vales on one side and breather on the other so that it actually has to suck through the crank case.
I just use a breather on the valve cover, I almost never hook up to the carb cover. Factory most cars did it this way.
Believe it or not a lot of the fellas still use the hose to the air cleaner and swear by it. That was why I mentioned it. One of the things that bothers me and probably shouldn't is the guys that use the old blocks and stuck the PCV valve in the road draft tube hole. Then they use a front fill intake and use a breather cap instead of a sealed type cap. I am probably way off base but in my mind all that does is ventilate the lifter valley.
there is an "open" PCV system, and a "closed" PCV system. The open one has a breather with no hose to the air cleaner. The closed one has the hose. The difference is that the open system will vent vapors to the atmosphere when there's too much blowby for the PCV valve to handle (like when you stomp on the gas pedal, or when the engine gets tired). The closed system burns these vapors. With a few old hot rods driving around occasionally with open systems, it's not a big deal. But having 100 million cars like that, makes for rather dirty air in big cities. That's why the closed system was required on new cars by the fed gov't in the late 60s.
Porknbeaner, you're right it will ventilate the lifter galley well, but the whole system(crankcase to valve covers) is still connected by drain holes, push rod slots, etc. Better than sealed up tight, and letting crankcase pressure try blowing out anywhere it can.
The engine in my convertible, a 455 Oldsmobile engine had a hose that went to the air cleaner on the left bank and the PCV valve in the right bank valve cover. This the way that I set it up when I built the car
In my feeble mind I believe that may not be a bad thing. It relieves the crankcase pressure, evacuates the blowby gases(because there are enough connections between the pan and valley) while avoiding the oil mist in the pan area. Seems best not to suck that into the intake. As a matter of fact I'm working on an old flathead Mopar six and am trying to decide whether to use the road draft hole, or make a new port in one of the valve covers, for that very reason. There is very little oil in the valve area in those so that could avoid all that mist from the crank throwing it all around. edit to add: I also think I'll use a sealing type oil cap, weld a tee into the fill tube and route it to the air cleaner base. All this plus the full flow filter mod in hopes of keeping the oil clean a free of water vapors.
We used to use a vacuum pump from a Ford on cars that we thought were going to have too much crank case pressure build up. its been a while since I set one up that way. They actually make expensive race pumps but the Ford pump is the cheap way out. Ok that has nuthin to do with the thread but it jumped in my head and now its gone. Thanks
I might be totally wrong, but didnt mid 60's Corvettes have a PCV valve screwed into the carb base with the other end of the hose attached to the oil fill tube at the front of the intake (which had a non vented cap on it)? The valve covers had no breathers. Does this sound right? If so, how was air getting in on that arrangment?
Yes but those blocks still had road draft tubes out the back of the block but instead of going down to the ground they were plumbed into the air cleaner. At least the 65 327 I worked on in the early 80's was set up that way.
Chevy used the rear hole in the block and the oil fill holes for the PCV system, until they changed the block design in the late 60s, and went to holes in the valve covers. They both work ok.
Your right pork it is not an ideal setup,the best is the fresh air in one valve cover and crankcase fumes out the other so the whole crankcase is ventilated but it is better than nothing for the guys who unable or unwilling to put holes for the necessary fittings in the valve covers.
Not to hijack the thread, but I'd like to add a 2nd valve cover breather on my car. The driver side I have a breather/oil fill. On the passenger side, I have a PCV valve going into the carb base. I was looking for a breather that would still allow the use of a PCV valve in it, any ideas? It may even help the OP and others here.
If you put a breather near the PCV valve, then air will take the path of least resistance, and go from the nearest breather to the PCV valve. The PCV valve won't really do anything. You might as well just have two breathers, and change the oil often.
OMG! Is that a Chevy engine I see in that Ford. The Ford lovers have you in there crosshairs. Be forewarned. You must be a Hot Rodder.
A LOT of newer cars DO have a pcv system. Most of them vent into the air cleaner housing and the pcv valve is actually built into the valve cover. If you need a new pcv valve you don't just buy a 3 dollar valve and pop it in. You buy a 100 something dollar valve cover and replace it.
On the hemis there was a piece of rubber (?) sheet attached to the valley cover that hangs down across the valley in theory blocking the direct flow under the cover making it go through the crankcase.
I think that Ford and MOPAR both used a breather looking deal with a PC valve in it. I actually run a valve in my pass cover (like you) and double Almquist mushrooms on the driver side on my old motor. Seems to work for me.
I bought a PC Valve for a 65 Chevelle V8 because it screwed into the carb base. I tapped and threaded the adapter for the carb change we are using on the Howard 5-2 manifold. It's feed line comes from the old side breather on the side of the crankcase. We just have a breather oil fill cap on the rocker arm cover. Hoping the system will work.
The "Closed PCV system" typically picks up fresh air from just outside the air filter, and under heavy load (or a worn engine) will blow oil laden air onto the filter, soaking it with oily blowby. I like to modify this system so that the fresh air intake is inside the filter, and excess blowby is directed straight down the carb throat:
^^^^^ I had an off topic car that was plumbed like that. Trouble was when oil that collected within hose got puked out it was like a James Bond smoke screen.
A smoke screen would be fine with me! But I only found a few ccs of water in the line when I took it off and poured it on me without thinking about that it's a liquid trap.
When it's working correctly the vapor is sucking thru to he line to the valve into the intake so this is a good system. I'll bet there's not much smell.