Blow by

[Dyoel182]

Originally Posted By: BarkerMan
Experimenting has proven more useful than common sense but I think that even in street engine these devices are worth the trouble just because the stuff that comes out looks nasty.


Exactly what I think and why I use them and have made them for other people. The first time I did an intake manifold job on a high mileage car about a quart of sludge poured onto my foot and since then I've been trying to filter out as much as possible. My first catch can rig was a metal can with steel wool but it was such a pain to clean and empty that I went with the air tool filters that I saw on a Honda board.

 

[Oilgal]

vacuum_6

Those CFM rates, for the air drill moisture separator, apply to the same with that filter left in place, and as I am sure you are now aware, that filter must be replaced with a central tube anyway in order to make a catch can out of it.

The Jegs unit you linked to, looks to be about the same size or smaller, than the air drill unit I recommend for the conversion. It costs twice as much though, that's Jegs for ya, and I will never shop Jegs again. They pestered me with spam for two years after my last purchase. I recommend Summit Racing instead. They are really good. I love those guys.

 

[Oilgal]

Originally Posted By: BarkerMan
We have found that diffusing the flow is more important than baffles, that is changing the volume of the space the vapors travel through.


That is what my my builder friend showed me also. No need for a baffle or steel wool in my NA 3.0L.

However for an engine with, for whatever reason, a higher PCV flow rate, you may need the greater volume of space a larger can affords, and perhaps even added baffles and/or some condensate medium like steel wool.

 

[BarkerMan]

If you try the cans-in-series development approach also try taking vacuum reading before an after. This is called leaning and with a little bit of messing around on Saturday you can do a lot toward cleaning up the inside of your engine. I have found that experimenting with flow and diffusion while using Auto-Rx you can help the process move along. This kind of device with Auto-Rx really works and the stuff that comes out is really nasty. If you would not pour it back in your engine it's worth getting rid of.

 

[Oilgal]

Hi BarkerMan

Sorry to ask such silly questions, but I am afraid I have to, in order to understand even simple stuff often. Einstein I'm not.

I definitely agree we shouldn't return the condensate back to the engine, and really that is a weak spot in my forward PCV hose setup. I don't understand though, how experimenting with catch can flow and diffusion helps the Auto-Rx process, and I would sure like to. So would you teach about that?

Also I am wondering about what you said here.

"Restricting the volume in the path drops the pressure and expanding the volume raises the pressure."

Did you really mean that the other way around? If not, please teach me about that also, because to my mind it seems reversed. Like I said, I'm definitely no Einstein.

 

[BuickGN]

Keep in mind this car seems to have problems with oil burning/ring seal. On top of that, I don't know the guy's combo but with the heads he has it has the potential to be a deep 10 second car so it's going to see a lot of cylinder pressure/blowby. This is why with mine I said screw it and change the oil every 500-1,000 miles and run breathers vented to atmosphere.

 

[BarkerMan]

Look at a carburetor. The venture restriction causes a pressure drop. It increased the flow rate and sucks fuel out of the bowl and into the engine. It sounds wrong but it works. It’s the same with increasing the area. The flow slows and the pressure goes up.

If you can remove more vapors out of the crankcase and get the gunk in the fumes Auto-Rx will do a better job of cleaning the oil. The vapor in the crankcase will be able to support new gunk which the catch can will continue to remove and not pass back into the combustion process which is not perfect but the blow by will be cleaner as it gets back into the crankcase.

 

[Oilgal]

You're right. I think I may need a longer catch can reservoir.

 

[kokopelli]

I thought my car's PCV set-up was a little strange -- it uses an Oil-Air seperator rather than a PCV valve.... but, it appears that the set-up I have is similar to a catch-can...

 

[Oilgal]

Originally Posted By: kokopelli
I thought my car's PCV set-up was a little strange -- it uses an Oil-Air seperator rather than a PCV valve.... but, it appears that it the set-up I have is similar to a catch-can...


What make model year is that kokopelli?

 

[kokopelli]

it's on the 97 pontiac with the GM 2.4L (LD9 engine) Twin Cam... the 3100 v6 during the same time used the PCV valve...

 

[Oilgal]

Ooooh. Turbo then?

 

[Gary Allan]

A filter is not always necessary. You just need to provide a chamber for the velocity to go to a near standstill. The heavy stuff will sink out. Unless you're running at extended high output, the thing should work just fine. It's sort what they do on my jeep 2.5. They just put a massive plenum over the throttle body (not done on the 4.0) and the vent enters from a recess (like a drain) in the floor of it. I haven't taken it apart, but there's no service interval for any filter/baffle, so it has to just drain back to the valve cover if anything of substance accumulates there.

 

[Oilgal]

Glad you chimed in on this Gary.

After kokopelli mentioned the oil air separator, I did a search on it, and I found two neat tutorials on how make one. Apparently that is the 'non red neck' name for a catch can.

Building An Oil/Air Separator

Building An(other) Oil/Air Separator

I would still like to find that Pontiac O/A separator part for sale somewhere though.

 

[moribundman]

Originally Posted By: Gary Allan
A filter is not always necessary. You just need to provide a chamber for the velocity to go to a near standstill. The heavy stuff will sink out. Unless you're running at extended high output, the thing should work just fine. It's sort what they do on my jeep 2.5. They just put a massive plenum over the throttle body (not done on the 4.0) and the vent enters from a recess (like a drain) in the floor of it. I haven't taken it apart, but there's no service interval for any filter/baffle, so it has to just drain back to the valve cover if anything of substance accumulates there.


They stole my Audi's basic PCV design.

The only problem is that that much blowby even gets into the plenum.

 

[7055]

Originally Posted By: Junior
Originally Posted By: 7055


Thats not the only reason, there needs to be vacuum in the crankcase, thats why the PCV is hooked up to a source of vacuum (your intake). It needs vacuum to vent of the blowby and help pull the oil off the walls and keep it in the oil pan where its needed. This is even more so important on cars with forced induction. The PCV is a ventilation system, it needs to be hooked up to vacuum to ventilate the crankcase.


What? A vacuum in the crankcase is not necessary as long as it is vented. Think pre 1964.

It does help the seals live a happier life and modern cars are designed to operate this will and will probably not run correctly without but a PCV system was only develped for emissions


"During normal compression stroke, a small amount of gasses in the combustion chamber escapes past the piston. Approximately 70% of these "blow-by" gasses are unburned fuel (hydrocarbons) that can dilute and contaminate the engine oil, cause corrosion to critical parts, and contribute to sludge build up. At higher engine speeds, blow-by gasses increase crankcase pressure that can cause oil leakage from sealed engine surfaces."

The purpose of the pcv is to vent off these vapors that cause sludge, and the blowby. If its just vented to the atmosphere the blowby can escape but you're not venting the crankcase of these harmful vapors. I'm not saying you can't do it but its kind of defeating the purpose.

I've seen people vent their pcv to the atmosphere on turbocharged cars and it causes boost to build up in the crankcase from the blowby, it'll shoot your dipstick out and coat your engine bay with oil or blow a headgasket. The reason for this is the high pressures in the crankcase simply can not escape fast enough unless its routed to vacuum when at WOT.
Vacuum in the crankcase is good for the car though be it naturally aspirated or having forced induction. Infact it is not uncommon to see people route the PCV to the exhaust, the reason for this is the high amount of vacuum it provides. The PCV is certainly not for emmisions only.

 

[Gary Allan]

Quote:
The reason for this is the high pressures in the crankcase simply can not escape fast enough unless its routed to vacuum when at WOT.


..err..help me out here. Just what vacuum source does it use with a 'charged engine at boost? For that matter what Hg readings are you getting @ WOT in a NA engine

? Now if you're saying the fresh air vent, that might be behind the air filter (depending on year) in the non-pressurized plumbing,..then "sure", but that's hardly a vacuum. Well it is, but probably measured in inches of water column. Now if the year is right, a venturi extractor in the exhaust would do the trick. There you can get a vacuum.

 

[7055]

Originally Posted By: Gary Allan
Quote:
The reason for this is the high pressures in the crankcase simply can not escape fast enough unless its routed to vacuum when at WOT.


..err..help me out here. Just what vacuum source does it use with a 'charged engine at boost? For that matter what Hg readings are you getting @ WOT in a NA engine

? Now if you're saying the fresh air vent, that might be behind the air filter (depending on year) in the non-pressurized plumbing,..then "sure", but that's hardly a vacuum. Well it is, but probably measured in inches of water column. Now if the year is right, a venturi extractor in the exhaust would do the trick. There you can get a vacuum.


A source of vacuum preturbo ofcourse, after turbo wouldn't be a vacuum it would be boost

at WOT in a N/A car you should have 0 vacuum, I don't know what brought that up

I mentioned that already

The whole point I'm trying to make here is the vacuum helps ventilate the crankcase, and its more important on turbo cars. I'm not sure where we're are going to us.

 

[BuickGN]

On the GNs, there is the PCV valve in the intake manifold that goes to the throttlebody. Then there's a hose that goes from the passenger side valvecover to the inlet side of the turbo, right before the compressor.

There's boost on the throttlebody at WOT and very, very little vacuum on the inlet side of the turbo. During this time, the valve is supposed to block boost from pressurizing the crankcase. On some of these cars that run well over 20psi the valve lets boost past.

 

[7055]

^^^true

Quote:
During this time, the valve is supposed to block boost from pressurizing the crankcase. On some of these cars that run well over 20psi the valve lets boost past.


On my car boost got past the pcv valve even at 10 psi, I tested it. I remedied the problem with an aftermarket checkvalve.