PCV, Vent by intake vacuum or exhaust vacuum

[untouchablecc]

I have been thinking about this for a while and have not found it on here.
I know the popular way to ventilate crank case pressure is through a catch can and to the intake pipe that runs to the turbo.

The other way that is not seen done on our cars is taking a line and running it to the exhaust and cutting a 15 degree angle into the exhaust and using the vacuum from the gases flowing out the exhaust to decrease crank case pressure.

This is nothing new. It has been around for years on old V8s and i believe boosted Hondas are now doing this. I wanted to see what anyones thoughts and opinions were on this. Running a line to the exhaust is much cheaper then spending money on a dual catch cans and stainless lines.

 

[delta448]

On a Mass Air equipped car, it's metered air. Also, the vacuum created just ahead of the compressor inlet is waaaay more than you'll find using a crude venturi stuck in the exhaust.

 

[tenn-gsx]

Im going to be putting an exhaust ventilation setup on my car. I personally feel that if you need more than a few psi vacuume then there are other issues that need to be addressed.

 

[Calan]

I have been thinking about this for a while and have not found it on here.
I know the popular way to ventilate crank case pressure is through a catch can and to the intake pipe that runs to the turbo.

The other way that is not seen done on our cars is taking a line and running it to the exhaust and cutting a 15 degree angle into the exhaust and using the vacuum from the gases flowing out the exhaust to decrease crank case pressure.

This is nothing new. It has been around for years on old V8s and i believe boosted Hondas are now doing this. I wanted to see what anyones thoughts and opinions were on this. Running a line to the exhaust is much cheaper then spending money on a dual catch cans and stainless lines.

It's been discussed quite a lot here actually. I believe member SOADweskey actually did some tests and verified that the exhaust doesn't create enough of a vacuum to really be effective (as Zack stated above). I know Paul Volk (99gst_racer) was also looking into it at one point.

The other problem you have is that on a car with a fully functional bi-directional PCV system, you will be pulling exhaust gases back into the engine and intake during off-boost conditions. I don't even like the factory EGR myself; much less an additional source of it.

A good filtering can with a low pressure drop, tied to the turbo inlet is still the best solution.

 

[untouchablecc]

Well crude is an opinion. If done right you cant even see where it enters the exhaust so i don't see how its crude, simple would be more suitable. If it works thats all im concerned about.

I was reading on the link forums about this some and the theory i have been getting from there is that if your intake pipe is small enough to create the kind of vacuum needed to draw out the crankcase pressure then its too small of an intake pipe. Im not sure how true that is but me and a friend of mine have been going back and fourth on this subject. He is saying that if you run a large enough intake pipe it wont create enough vacuum. I kinda disagree because of the videos of cameras in intake pipes and watching how much air a turbo really draws in.

Well noted calan on the bi directional PCV system and i am familiar with it. Do you think a larger check valve could be used to keep the flow of exhaust from coming back into the crank case?

 

[delta448]

Maybe I should have said simple. I didn't mean for "crude" to sound condescending. But in my opinion, a venturi to draw air or fluid should be well thought out and designed, which I doubt any installation in an aftermarket post turbine exhaust pipe would be. The main principle of how well a venturi works is dependent on velocity. A 4 barrel carb sitting atop a big block spinning at 5500 rpm is going to have a shitload of vacuum to pull all that needed fuel out of the venturis and into the intake.

The argument about too big of an intake pipe size works on the exhaust side too, too big there and air velocity drops. The difference is; when you're talking turbo performance a big diameter low-restriction exhaust is a must have, while compressor inlet size is solely dependent on the turbocharger in use. You can design a long bell-mouthed air horn for the compressor to ensure high velocity at the inlet. On the exhaust side, creating this same shape makes a restriction to flow and hurts performance.

 

[Calan]

I was reading on the link forums about this some and the theory i have been getting from there is that if your intake pipe is small enough to create the kind of vacuum needed to draw out the crankcase pressure then its too small of an intake pipe.

Not sure what the evidence for that is. Several of us have done testing and taken actual measurements, and even with a 4 inch intake there is plenty of suction for a well-designed system. The intake should be sized for the turbo's inlet diameter and ability to move air...so in theory, there shouldn't be much of a difference in vacuum if you increase the turbo/inlet size.

You need enough vacuum to overcome the pressure drop in the venting system, and to overcome frictional drag and other restrictions to the air flow. The problem is that using an exhaust tap on our cars probably isn't going to provide that amount of vacuum, unless it's very well-engineered for optimum performance.

Well noted calan on the bi directional PCV system and i am familiar with it. Do you think a larger check valve could be used to keep the flow of exhaust from coming back into the crank case?

Not if you want to continue providing fresh air to ventilate the crankcase with. By definition, a check valve makes a bi-directional system one directional.

Why are you opposed to the proven method of using the intake?

 

[untouchablecc]

To be honest with you the main reason i second guess the intake set up is because a friend of mine has been debating with me on it. He knows his stuff i have never doubted that and he is a member on here and has tuned some really fast cars that are also on here like talondave. He was telling me that the exhaust vent was the better set up based of off what he was finding on link forums. I wish i was better prepaired with more evidence but i entern and work so i dont have time to palasade across the internet looking for it. I feel the intake venting would work more effectively because a turbine is going to draw more air then the vacuum of an exhaust in my opinion but i was just trying to be open minded about the subject.

I was also considering the cost of a catch can vs running a hose to the exhaust. I dont want to have a ton of money tied up in a dual catch.

 

[Calan]

I definitely understand your point about cost, but you need to consider the goals of the car. Most of the fastest cars don't have an inlet on the turbo anyway, so they obviously aren't going to go that route for venting the CC. (And they probably rebuild the engine more often than I change my oil).

I've seen many fast DSM's with nothing but a cheap filter hanging off the VC port but that is far from the best solution if it is a regularly driven car. For a street car that gets it's oil changed every 2500-3000 miles, has to run at least somewhat clean, and is pushing any significant boost...I will stand by my opinion that using the turbo inlet with a good catch can is by far the best method of relieving crankcase pressure. And I have many references that can back that up. There are exceptions of course, but not as many as a lot of people think.

Out of curiosity, do the people arguing with you have any numbers or hard evidence, or is it just an opinion? Nothing wrong with an opinion of course, but I think people should be able to back up their claims with at least some type of evidence. If there is any evidence that the exhaust method or a can open to atmosphere does a better job of relieving crankcase pressure than a proper turbo inlet setup, I'd like to see it.

Have you read through Paul Volk's thread? http://www.dsmtuners.com/forums/custom-fabrication/372279-my-new-crankcase-evactuation-system.html

It contains some pretty good information. There are several other lengthy threads scattered around with good information also if you haven't seen them.

 

[Kruger]

Hey guys, Im aware that this thread is quite dated, but I have a question regarding the use of the intake pipe as a vacuum source. Do the fumes affect the intake air quality? Will it negatively or positively affect performance at high boost? In essence youll be getting less oxygen, but recirculating exhaust gases has been known to fight knock in some instances. I cant seem to determine this, even after a wide search.

 

[TSiAWD666]

The crank case gases will generally have more oil in it than fresh air and will lower your effective octane rating. A good catch can should filter out much of the oil but as to how much and how that changes your octane rating I don't think anyone has quanitified, at least not that I've found scouring the web.