PCV under the boost issue ...

**Tim@NCTSLLC** · 06-08-2011, 09:57 AM

This whole topic seems to have become far more confusing then it really should be. You really do not need some really expensive components to put together an effective system. Unless you are running some really high boost pressures, then you should not be venting to the atmosphere. Even so, venting to the atmosphere is usually indicative of other issues in the engine.

Back when I was racing offshore powerboats, my 28’ Cigarette was running a pair of 600 crank HP, normally aspirated Chevy 383 stroked small blocks. In an offshore race, the engines see brutal conditions, basically running at 5400 – 5800 rpm or more for an hour non stop. I was puking oil out the breather caps. One of the big contributors was the oil pump itself. I was running a high pressure, high volume pump. Running this pump design (high volume) was putting far to much oil up into the head and valve cover area.

Initially I solved the issue with carbon fiber valve covers with two 6” tall breather towers on each valve cover. Thank goodness for the sponsor that provided them, imagine buying 4 carbon fiber valve covers, and eight carbon fiber towers! Eventually the issue was cured by switching to a high pressure pump only, opening up the oil drains in the heads, and coating the valve train area and inside of the block to facilitate oil drain back to the pan.

Point is, part of the issue may be choice of oil pump, and the need to address oil drainage in the heads and possibly coating the inside of the block to speed up drainage. Add some boost pressure and likely some ring blowby from elevated combustion chamber pressures, and yep, you can have a big mess. My 383’s were NA motors, but were running 11.5/1 compression ratios.

The sketch below illustrates a simple setup to control pressure in the crank case bleeding past the PCV when the manifold is under boost. There are no vents to the atmosphere, and it is very important to connect the breather line to the inlet side of the SC or Turbo so you are pulling crankcase vacuum when not in boost so the PCV system will function correctly.

I do not run a catch can on my Turbo 300C, and I did not run catch cans on my other two turbo 5.7 Hemi vehicles either. But, all three were running stock internal 5.7’s, and no more than 10 psi boost. Nothing wrong with running a catch can, but I would hesitate to say they are a must have in all cases. If you are going to run them, make sure they are placed correctly as illustrated below.

The check valve that I use on my Turbo 300C was put together with parts from the hardware store. I will put together a list of what is used along with some pictures of how it goes together. If there is interest, then I will make assembled units available at a minimal fee to cover assembly. If I order the individual components in bulk, then I can likely put them together complete for $18 - $20 each.