Originally posted by RyaN95i4
Crankcase pressure will always build up inside the motor unless you have some means of relieving it. Remember, yours pistons have two sides -- they create pressure on both sides. The PCV only works under high vacuum situations, like idle and decel. Otherwise, it is suppose to be closed to prevent positive pressure entering. Running a check valve will help prevent boost from pressurizing the crankcase further, but it still doesnt allow crank case pressure that builds up normally any where to escape. Thats why your dipstick tube is getting blown out (and also why supras like to blow front main seals) the v8 guys have run vacuum pumps on track cars to pull that crankcase pressure out -- having the crankcase under constant vacuum also allows the rings to seal better and reduces drag in the motor...high horsepower v8 cars will see gains as high as 40-60hp using a vacuum setup. (as well as having much cleaner oil). Mechanical vacuum pumps are great because theyre pulley driven and give a linear relation in motor speed and how much vacuum is pulled, but theyre expensive and need frequent rebuilds. Electronic vacuum pumps can be had for less (smog pumps), but they dont tend to last long and its difficult to set them up so that they draw more vacuum at higher rpm/boost and less at lower rpm/boost. Another means to have a constant vacuum source is using slashcuts in the exhaust -- they generate vacuum through the bernoulli effect. This eliminates crankcase pressure and keeps the crankcase in vacuum. Moroso, Summit, Mr.Gasket, etc all sell kits that include slashcuts and check valves (to keep exhaust from entering the crankcase in case of a backfire). The supra crowd picked up on this method a while back too You can either just burn off the blow-by in the exhaust, or run a sealed catch can inline to avoid smoke from buring blow-by The problem with using the pre-turbo intake as your vacuum source is that very little vacuum is generated pre turbo unless you have a very restrictive intake. You can try to just vent the crankcase to atmosphere, but it doesnt appear to be an adequate means of relieving crankcase pressure -- take a look at the supras who blow front mains frequently and most of them will just be venting the crankcase instead of having some type of vacuum source to pull pressure out added benefit of having the crankcase in vacuum is that any oil leaks will suck in instead of blowing out -- meaning they will either be sealed or suck air in instead of blowing oil out. With my most recent build, I was researching all the different ways Ive seen pcv and catch can setups and the exhaust evac setup seems to be most ideal: constant state of vacuum that increase as the engine is driven harder (more exhaust flow creates more vacuum) and total isolation of blow-by and crank case gasses from the intake tract