Thread: PCV and Intercooling

brought over from a hijack of someone elses thread...

Originally Posted by Trannyman95

Since I went to school for engine rebuilding and automotive specializing in general, especially the performance end of things, I am well aware of how the system needs to function. Maybe I should grab one of my engine books to bring along to Branson since pictures speak louder than words and it may not seem clear. Here is how it works...... When the engine has vacuum in the intake manifold ie idle, light, part throttle conditions airflow is drawn through the pcv vent hold in the throttle body which is the one that passes through the intercooler and into your modified/passage machined lower intake manifold to work with stock pcv type operation. This allows fresh air to be drawn through the crankcase and also prevents you from putting a larger vacuum on the crankcase which will make the noise you mentioned and also try to suck excessive of oil vapor into the engine. ALL engines have blowby to some extent and must have fresh air pass through the crankcase to allow it to vent off. The other end of the system is your PCV valve that is in the blower housing. This is a calibrated bleed so to speak that allows engine vacuum to pull the crankcase pressure/vapor through the pcv valve so it wont build up. This is vented into the top of the inlet of the blower housing and this is why you see wet rotors and lower intake as it is thousands of miles of pcv operation which will have a very fine oil mist to it often. The PCV valve has a checkvalve and spring inside it so it will only flow one way, or with vacuum on it. Now once you go to 0 vacuum or into boost the PCV valve no long is working the same and the crankcase vapors are vented in reverse through the passage that goes back into the throttle body. These gases and vapors are carried through the throttle body and all the way through the inlet of the blower. Along with any pressure potentially built up in the crankcase helping push these vapors back out the incoming air across the hole in the throttle body for the pcv passage helps draw them out. Look at it this way.... You got to McDonalds for a pop and get a good sized straw with it. Try blowing through this and sucking through this.... you get the idea. NOW do this with a coffee straw! I think you know where I am going with this, you have a coffee straw to breathe through with your modified-added pcv passage intake. Back to what I mentioned earlier once you go above stock such as spinning much higher rpms and adding more boost you need more ventilation because the crankcase pressure is going to become higher than on a stock car that's system was designed to perform adequately with. Race engines dont car about the whole spectrum and only run breathers on the valve covers. Your question about only the front half of ventilation... The crankcase is common to both cylinder heads and sides of the engine so it really doesnt matter though you often find the inside of the rear valve cover a bit dirtier than the front one. The PCV system was really used standard back in around 1965 from an emissions standpoint as it used to just get vented out of the engine through vent tubes and some cars with a draft tube that would run under the car, then to the PCV system which will send these vapors back through the engine to reburn and let off less emissions and not have raw oil dripping on the ground. I hope this helps clear up your thoughts on how it works.

Originally Posted by IndeedSS

Now that's what I'm talking about! Finally a blower PCV specific write-up. This is one I will want to bookmark.

When I said half of the system I didn't mean the engine itself as in the 1-3-5 front half, but the half of only drawing in air and not venting. If you are saying this,without any valve acts as both then I can see where a TB would need constant maintenance without an oil catch can.

Now the big question as related to the straw analogy. drum roll please. I know that the passage in the throttle body is small. The PCV when open apears not to be able to pass the volume of air that the top fitting could, if there was no valve in the middle or the small opening on the bottom (I can still taste the gas..I'm more of a hands on learner LOL). Nevermind the passages on the blower, because we don't know if the sizing in there was related to volume required, or a matter of casting needs, or a combo of both....

finally back to the straws. How do we know that the coffee straw isn't enough but soda straw was used? I'm only asking because while the answer may seem obvious, I don't know that it is...yet especially with the lack of problematic PCV history.

I love this schstuff...it's how I learn. You know I take nothing handed out, without questioning why. It's not personal, it's just my SOP.

Originally Posted by Trannyman95

I know Lee, thats I am try to break things down and make it easier to follow And you know I dont have an issue with that! An apples to apples comparison is the only way to see what is going on. You are correct that the hole in the throttle body isnt that large, but it is much larger than the bottleneck downstream that was added in that didnt exist in stock form. Like anything else that have to move from A to B and kink, bend, tight corner, etc will restrict flow, especially with all of the above PLUS a greatly reduced size is at hand. The smalled point of the passage is the hole in the throttle which is the tail end of the path. The modified intake is the largest restriction right at the start of the path where it needs to be the largest in order to move adequately from A to B. The only way to know what you have is to put a pressure gauge right on the fill cap and go make some WOT runs and see what it does. Again this really isnt comparing apples to apples unless you do it as your car sits THEN pull the IC back off and test with factory operation...... But I know you dont want to tear the car back apart to find out lol! Also you will have to run the same boost level and rpm for the A-B comparison otherwise it wont be as accurate.

Originally Posted by IndeedSS

What you say makes sense, and I get it. I'm just wondering if it is possible that no harm is being done. Without doing what you mentioned, we don't have anything to really go by other than past history and that looks favorable. And you are right, I'm not touching anything.LOL After all it took me a long time to carefully assemble this in the first place.

OK, I have to fess up.
I may have started Lee going down these paths of thought. I have been pummeling him with pcv questions while we were working on his car (well I was mostly just holding a light or something while he worked).

I have the squeal on my zzp installed stage 2 intercooler and had had it back to them once to look at fixing it. I have never liked the design and the more I learn about how the pcv system is supposed to work the more I think this is a sh*tty solution.

Dave, I am definitely interested in you bringing one of your engine books to Branson. I've just bought a book to try to learn more about performance engine design. General knowledge that I can use to leverage what I do to my cars. Also I'd love to talk to you about what you thing we should do to my car as a better solution.

Adding this because it is relevent.
Zooomer was very quick to reply.

"We actually had a bit of debate about this in the shop. The small passage was approved by me, overruled by others here. We ended up building one and testing vacuum. We decided from the vac #'s that it would be ok and have been using them for over a year.You ahve to be very careful not to get RTV in the passage though."

You can't fault them for coming up with a solution that appears to have worked for the majority of the buyers.