Thread: Crank Case Ventilation fully explained. (Naturally aspirated edition.)

Your the man Cliff.

The Dash English Lesson

^ Ha ha, win!

Good read

Great thread Ben learned some new stuff too .

My old engine had lots of blow by, my intake manifold was soaked in oil all the time. After doing a new engine swap, stock setup worked just fine.

The Roller Rocker valve covers will probably be a good step to reducing oil blow by. Though Rob mentioned that RR"s do get a lot of blow by...

Just checking, but all your pics show only positive feed out from the crank case to the intake pipe and feed back into the motor via the throttle body.

1 is there definitely a restrictor in there? i haven't seen one in any JDM stuff i work on, well noticed anything anyway. or any sort of fire suppressor, Maybe that is a USD thing and something to do with your EGR system?

2 My understanding is that on a high manifold vacuum situation when fumes are been drawn through the PCV valve this hose from the intake pipe supplies fresh air back into the crank case to reduce the amount of concentrated blow by hydrocarbons as a too high an amount of fumy air entering the combustion chambers, especially at low rpm would result in fouling of plugs, misfires or erratic idle.

I realise at low vacuum situations such as WOT that the PCV valve will be closed and blow by pressure in the crank case will be forcing fumes into the intake pipe, But this pipe is also a fresh feed back into the crank case

I know. This is a problem. I'm still working on some diagrams that will show more completely what happens as far as air entering the system from the intake pipe.

On any USDM engine I've worked with there was a restrictor. It's integral to the intake boot. Maybe this is not present in JDM engines, but I bet it's there. I believe it is to keep the idle down, because as you explain and I'm going to explain further, air is sucked in from the intake into the engine bypassing the throttle plate and the idle control valve so it has to be controlled somehow.
Restrictor pics:





The fire suppressor looks like a large metal section of pipe cleaner. I don't believe it has anything to do with the EGR system. I think it is there to prevent a backfire from igniting the crank case. I removed mine the first time I saw it thinking it was left there by a mechanic while cleaning the hose. I didn't learn what it was until much later. So I don't have any pictures of it, but others will attest that their engines had it too.

You are correct. Air is drawn in during these situations and contributes to the idle air as well. I'm not 100% sure it does this to prevent spark plug fouling and such or if it is a necessary side-effect of the system, but it does happen. I'm hoping to update the thread with an explanation of that soon.

Old heads called this piece a "hogs tail" pipe cleaner. It is used ot stop large debris and prevent fire from happening. When I cleaned my throttle body, I pulled this sucker out figuring the same thing you did Ben. Then I put it back after my Dad told me to quit fucking with it.

Good thread. Just waiting for the correct way to by-pass the system, make the engine look and be cleaner, etc... Both the caps and the breather are no-no, so how to do it?

after reading that i returned the original setup, and the car start to behave poorly, it loose some performance ( just a bit ) and very bad loopy idle so i remove it again both PCV and intake hose and loose them to the air the car has perfect idle and perform better, i don't know why but the oil pressure is slightly higher without ventilation
my opinion is that this is a great article but in the real world the things are a bit differetn i've seen many times my filter to smoke that means that the gases pass throu, and ventilation works, and what about all the performance and racing cars with ITB's ? they don't have this everything is led to the air ? are those ppl stupid to risk their expensive investment ?