check valve behind pcv
 

Might be a good idea for all the people that are running boost to put a check valve behind the pcv valve and the crank case.last night i took the hose off and checked how easy it is for boost to leak out this inlet. there is no resistance at all and i could blow and suck air through this opening.should only be able to push air through but not come back.:iono:in my mind this means boost can leak out and into crank case:mad0260:Thanks to JAMESM who brought this to my attention with one of his old threads:thumbup: I am going to put a check valve in today and do a test drive to see the difference in boost pressure with and without valve. Might even put one on the brake booster line as i dont think it is a good idea for pressure to be going into booster then when braking, booster has to go back the other way when it is under vacume. Dieaframe is flexing one way then the other.please correct me if i am wrong:thumbup:

The PCV valve will keep your crank case from accepting manifold air. When there is pressure in the manifold it closes, just like a check valve.

http://civilianjeep.info/Strenk/Emis...v_function.gif

I thought the brake booster line already had a check valve in it?

The brake booster definitely has a check valve in it, but I am still of the opinion that our PCV or Positive Crankcase Ventilation hose off the back of the manifold has nothing in it to prevent pressurizing the crankcase with boost.

@King Tut how does the PCV hose connect to the intake manifold? if it attaches to a threaded hose barb fitting you can probably find an OEM PCV valve off of something else to thread in there.

seems odd that they would do that, though, nearly all the N/A cars I've seen still have a one-way PCV valve of some sort.

There is a fitting that screws into the block/crankcase and then there is a molded rubber hose that goes from that fitting to the plastic fitting on the back of the intake manifold. Nobody has shown proof that there is any kind of check valve or one way valve on that fitting that screws into the block. There definitely isn't one in the hose.

Subbed

@King Tut normally there isn't any check valve on the block, just on the intake manifold.

how are people routing their PCV hoses such that it pressurizes the crankcase?

http://i.imgur.com/5iPTJ9U.jpg

@King Tut when running an oil catch can for the rear PCV, does it matter if the check valve goes before or after the occ?

Would you also place a check valve on the hose that runs from crankcase vent (under the AC compressor) to the intake pipe? Mine's a sprintex setup.

That depends on whether your catch can is setup to withstand boost. I wouldn't want to chance it, so I would place the check valve between the catch can and the intake manifold.

The intake pipe never sees boost, so no need to worry about a check valve on that hose.

since i have found out there is no check valve in the manifold and have since put one in there the boost on my car has gone up about 1.5pounds and is pulling even harder than before.now all i have to do is build a 3" mid pipe with high flow cat and see if i can get some more "boost" out of this thing "ye haa".

What size check valve did you use?

+1, details please

This works fine: http://www.usplastic.com/catalog/item.aspx?sku=64175