okay guys here it goes.... i took my PCV off my car and it was in proper working condition. what i did was duct taped the end of the PCV valve closed so no air can get in or out(very ghetto i know and then put it back in the hose. so essentially i blocked the line coming off the IM. i then left the hose coming from the black box venting into the atmosphere. my question is "will the crankcase properly vent into the atmosphere or does it need that vacuum pressure in order to get it out?" is this going to hurt anything running it like this? the reason i am doing this is because i was afraid that when under boost i was pressurizing the crankcase and creating blow-by and thus causing excess smoke out my exhaust. i always just figured my car was running a bit rich due to using a greddy blue box for management. another reason i tried this is because my idle would bounce from 1k-1500. now the idling is more stable. i initially thought that the irratic idle was due to slightly retarding my timing on the distributor, but i dont think that is the case. this is a homemade setup BTW on a D15b7. so my main concern is, "Is the crankcase going to properly vent without the aid of that vacuum pressure from the IM?" thanks for your time guys.

 

it will still went but obviously not as well under vacuum. under boost i couldnt see it hurting anything because its letting crankcase pressure out and thats where youll see the most blowby of course. only negative it that its probably gonna be shooting oil on the bottom side of your IM...oh well

 

hmmmm. i went down the street and back and beat on it a little bit and it didnt spew anything out, but i realize that was like 1 mile of driving. i might be rigging up a catch can system here in the near future. i just wanted to make sure there wasnt another valve in that black box or something weird like that, which would cause no pressure release without vacuum, since on a NA car there is always vacuum.

 

its oil vapor so it takes a while to show

 

I would just put it back to stock... you will get better gas mileage.

Your PCV valve only let air go though one way... to your IM. Under boost the valve will close. Under normal driving conditions (out of boost) it will pull a vacuum in your crankcase, promoting better ring seal.

The only thing about your PCV system is it wasn't designed for boost. Under boost you will see high crankcase pressures because it has no where to go once the PCV valve closes, except for the valve cover vent. If you wanted to do it right you would need to run a line from your valve cover to the intake side of your turbo (between the turbo and filter) as there will be a vacuum there.

There are still other alterrnatives to this.

1) run it strait to atmostphere, this of course is the cheapest way, and deal with the bad mileage.

2) Run a crankcase evac system, these connect to your exaust and use check valves and venturi (sp?) tubes. This is the most cost effective as you can still use the stock PCV sysem and it will pull vacuum under boost.

3) Electric vacuum pump, these were found on older gm cars to help with the braking systems.

4) Mechanical vacuum pumps, they are used on race cars and are driven by your engine.

5) Dry/Wet sump oiling systems, the most expensive way to go but the best also for other reasons.


But if you are not boosting really high, I would use the stock system. IMO

 

awesome, thanks for some good info man. i think i might just buy a new PCV and put it back together. but i was just driving it around and when i am WOT and boosting thru 1st and 2nd there seems to be less smoke coming from my exhaust. i run about 8psi on an IHIRHB5 because thats what the stock wastegate is set at. i would maybe do something with the intake pipe, but i run the filter right on the turbo so there isnt any piping, in which case i would have to make a intake pipe for it. my idling has gotten better. my PCV was in working condition but kinda dirty and im sure it had never been changed. the thing that sucks is that my motor has about 160K on it and i think they blowby is a little excessive compared to most. my compression is 155-140-140-140 she runs pretty good and still pulls alright though. does anyone else have some compression numbers for a sohc with that many miles for a comparison?? it has been boosted for about 10K of its lifetime. also ask around and if you know anyone with a D16 laying around hit me up. i could use a new project

 

i was reading a archieved post and a guy was saying anything over 130 and within 28psi of each other is acceptable, and EMERIKA said if you crank one cylinder more than the others it will throw readings off and i think we did crank a bit longer on that first one we did. so maybe they arent too bad. cyl 2-4 were all within a few psi. so i guess for the d15b7 those numbers are alright.