The only problem with that is it will only pull vapors/fumes from that rocker cover. It wont evacuate the crankcase nor the opposite rocker cover. If you can imagine the fresh air entering the engine on the p***enger side through the breather, flowing down through the head into the crankcase, then being drawn into the drivers side valve cover where the PVC valve is pulling the vapors from inside the engine crankcase into the intake to be burned. Simple and effective. Anything less and the oil gets dirty much faster. Chris
Yeah Dhondagod hit it perfectly. Also to note this not only scavages the fuel/crankcase vapors but attempts to put the crankcase in a vacuum which helps against oil seal blow outs and cuts down on oil seepage at seals
There's a old school rodder here in oregon bay area that uses a 7 lb. pvc valve on each rocker arm cover, with no breather other than the air cleaner. I've argued with him about it saying it would not vent the crankcase, but he uses it on several of his small blocks and swears it works and gives more engine va***n?
Sounds the the old school guy is trying to copy a pan vac system racers use. If he had a belt driven Vac pump to pull from the valve covers it would pull a good vac from the crankcase and give good ring seal.
Sounds like a load of **** to me. Pulling va***e without venting the crankcase somehow will pull in the weekest gasket or seal in the engine. When I was in tach school, the instructor did a cl*** demo blocking the crankcase breather and putting a va***e guage in the dipstick tube. If i remember correctly, the va***e guage was reading like 20 lbs with the engine running. After removing the obstruction from the breather oil began to streem out of the front main seal.
I amazed someone a little while back by changing how thier crank vent was connectted and showing how much better the engine ran as a result. I have to admit even I was surprized that it could make such a big diffrence. If there is a seal or gaskit that can not stand full manifold depression it wants changing anyway, the lower you can get the air pressure in the cases the less oil mist stays in suspension, and hence the clearer the motor runs. Race boys do indeed use a pump, no there is no vent back to atmosphere, idea is to pull the cases to an even greater depression than available at the manfold, at the very high speeds thier engines go, pumping and windage losses within the cases become significant, so ****ing the air out becomes worthwhile ! As a general rule you can't go too far wrong running a couple of pipes (one from each cover ) straight back to the manifold, a one way valve ( PCV ) in each line will stop any possitive pressure from accidentaly reaching the cases ( a 'pop back' ). The '**** through' plan was and is often used, where fresh air is drawn from a pipe in the airbox in one cover, through the bottom and then drawn via the pipe in the other cover in to the manifold, so that's air which is coming from outside, not going through the carb and then going straight in the in motor, effectively an uncontrolled air leak, well only limitted by the PCV anyway, not an ideal way of doing things, but often used none the less. The important thing is to insure that what ever you come up with the net effect is that the cases end up at lower than atmospheric pressure under all throttle conditions.
This may help some. This is the crankcase ventilation on a 49-53 flathead Ford long before the PCV systems. This seems to be the most misunderstood part of a ventilation system. Many people think of it as a pressure release point. It is not. Engineers designed their systems to get air flow though the entire engine including the crankcase. Look at how the air comes into the top oil fill breather. (that is why the breather has a filter element to keep out dust and dirt and the road draft tube at the bottom has none) It travels down into the lifter gallery, past the cam and crankshaft into the lower crank case, up through the front tube back through the intake manifold and down through the road draft tube on the out side of the engine into the air stream below the oil pan. The point is that there is air flowing through the entire engine. With both ends on the same V/cover, there is no air flow in the crank case. All of the moisture and acids that is developed in the lower end stays there and they are not eliminated from the engine. They are left there developing sludge and harmful acids. The purpose of any road draft or PCV system is to rid them the engine. Race cars that don't get much mileage probably won't show any long term affects over a few racing seasons. You can put more miles on a street car in a week than a race car will see in years. Racing solutions don't always work in long term street applications. Apples and oranges.....
Actually on a race vaccuum system we use a vaccuum regulator attached to a valve cover. Pulling vaccuum without a vent at high rpm will **** the oil off the rods and mains. When this system was "new" we had a customer that was pulling straight vaccuum with no breather/inlet and blew up 2 motors, added the regulator and never had another problem.
Am I reading this correctly? You had 20" of vacuum in the crankcase and the engine was sealed and running? Then allowing the engine crankcase to breathe by opening the breather started oil streaming out of the front main seal? I'm a bit confused here. ~~~~~~~~~~~~~~~~~~~ What the heck is a vacuum regulator? A new one on me.
http://www.dragraceusa.com/tech/AerospaceTechstory/aerospaces_vacuum_advantage_inex.htm Very good article on using a pump, looked for a picture the vac regulator, but no dice.
Well yes that explains it nicely, and it does say 'An adjustable relief valve is also included,' ie they use a simple valve limit the vacuum. However this is not contantly drawing fresh air into the cases, it's only there to limit the number of in/mg of vacuum in the cases, because a pump unlike manifold depression can just keep pulling more vacuum, untill the oil pan and rocker covers collapse. While the use of pumps to pull the blow p*** g***es out of the cases is definately race only, the general princibles are the same, if the vacuum is manifold derived rather than provided by a pump then it's limited anyway, so therefore the limit valve used with the pump is not required. Otherwise it's the same game, with the same aim of reducing the pressure in the cases. I have one for you, the pressure in the headers with a tuned exhaust goes negative for a fair part of the cycle, so it's not unknown for racers to use the negative part of the exhaust pressure cycle to provide the **** from the cases, if you want to search for more on this Mike at 'Eurospares' site has stuck a load of stuff on how to make that one work.
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