Q. I have seen the short answers about PCV systems. I would like to hear from a professional. I think a PCV system is a must-have for evacuating acidic and moisture-rich vapors from the crankcase. On the other hand, at WOT and near 0 inch of mercury, the PCV ceases to exist and oil (crankcase vapors) emits at the breathers. I am aware of the guys who build with low-tension rings and compensate with crankcase vacuum. I think a simple solution is a remote breather that won’t puke oil on hot headers and catch fire. Or design an engine with no blow-by. What’s your take on this?
A. You’re spot-on, Al. The best, for many reasons, is a no-blow-by engine. It’s amazing what the OEs have been able to do in the past decade with cylinder wall finish, piston ring design, and piston ring land configuration. When it’s right you have just about a zero blow-by engine. They had to do it for emissions regulations and they ended up benefited by increased performance and durability.
The positive crankcase ventilation system utilizes engine vacuum to evacuate crankcase vapors from the engine and ingest them with the intake air and fuel. You’re correct, as the engine vacuum drops (increase load) the PCV becomes inactive and all the ventilation is through the breather system. This is true at WOT, but we drive our cars on the street 99 percent of the time in high-vacuum conditions, which purge the crankcase of vapors through the PCV.
To reduce emissions, the vehicle manufacturers had to reduce the amount of this pressure, as it brought oil vapors from the crankcase and burned it in the combustion process. This was done by improving the cylinder wall finish in both the texture of the honed wall and the straightness and roundness of the cylinder. This made it much easier on the piston rings to follow the cylinder and seal. This allowed the ring designers to reduce the thickness and radial tension of the ring. This increased engine performance by reducing the parasitic loss of the rings dragging up and down the cylinder walls. Everything listed above was a major benefit. We’re down to production engines with 1.2mm-thick top and second rings with 3mm oil rings. To give you some idea how much of a reduction this is, a standard old-school small-block Chevy had 5/64-, 5/64-, 3/16-inch ring packages. If you convert this, a 5/64 ring equals 0.078 inch and a 1.2mm top ring equals 0.047 inch! That is a huge reduction in mass and drag.
In a performance, non-emissions application, an external breather for the crankcase is a simple solution. The main thing you need to make sure is that your engine oil reaches 212 degrees all the time to boil off the moisture that builds up in the engine oil from condensation. This is mostly where the vapor comes from on a properly sealed engine.
Yes, a zero blow-by engine is the best to keep the combustion gases from contaminating your engine oil. Total Seal top piston rings are the best we’ve come across for attempting this goal. They are great for racing engines, but for an everyday street car you may be lacking the long-term durability. Total Seal has two-piece top ring packs for just about every engine combination today. Keith Jones is a good friend who’s been at Total Seal for the past 12 years. He’s spec’d out every set we’ve used, and they do deliver on their name. Give him a call at 623.587.7400 for more information on your application, and he’ll give you the straight scoop. CHP