Catch Can Oil: Experienced Guys Only !!!!!
Race Director
Joined: Dec 2000
Posts: 19,304
Likes: 85
From: San Diego CA
Zee,
Actually, it's pressure drop that you should be concerned with. I use an online flow calculator that shows pressure drop, given a few variables:
Hose I.D. (in.) .375
Hose Length (ft.) 5.5
Flow (SCFM) 1.3
Gauge Pressure (psi.) 10
Pressure Loss (psi.) 0.02
As you can see, pressure drop is very low. As long as heavy debris is not being sent through the filters, there should be nothing to worry about. having the filters at the front of the engine bay gives you many more choices of filter types, as the super-hot area near the cylinder head is not the best place for anything containing plastic. Still, I measured less than 160F in that area with the data logger being insulated by airspace vs a metal bracket that many catch cans come with to bolt up directly to the very hot cylinder head.
Howie,
If those particulate filter elements had a habit of breaking up, Watts wouldn't be in business, and they've been around for a very long time. You needn't worry!
Dave
Actually, it's pressure drop that you should be concerned with. I use an online flow calculator that shows pressure drop, given a few variables:
Hose I.D. (in.) .375
Hose Length (ft.) 5.5
Flow (SCFM) 1.3
Gauge Pressure (psi.) 10
Pressure Loss (psi.) 0.02
As you can see, pressure drop is very low. As long as heavy debris is not being sent through the filters, there should be nothing to worry about. having the filters at the front of the engine bay gives you many more choices of filter types, as the super-hot area near the cylinder head is not the best place for anything containing plastic. Still, I measured less than 160F in that area with the data logger being insulated by airspace vs a metal bracket that many catch cans come with to bolt up directly to the very hot cylinder head.
Howie,
If those particulate filter elements had a habit of breaking up, Watts wouldn't be in business, and they've been around for a very long time. You needn't worry!
Dave
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Zee,
Actually, it's pressure drop that you should be concerned with. I use an online flow calculator that shows pressure drop, given a few variables:
Hose I.D. (in.) .375
Hose Length (ft.) 5.5
Flow (SCFM) 1.3
Gauge Pressure (psi.) 10
Pressure Loss (psi.) 0.02
As you can see, pressure drop is very low.
Actually, it's pressure drop that you should be concerned with. I use an online flow calculator that shows pressure drop, given a few variables:
Hose I.D. (in.) .375
Hose Length (ft.) 5.5
Flow (SCFM) 1.3
Gauge Pressure (psi.) 10
Pressure Loss (psi.) 0.02
As you can see, pressure drop is very low.
What I was eluding to is that if the line/catch can is too restrictive for the PCV system between the valley cover and the intake manifold then more oil will try to backflow between the valve cover(s) and throttle body if it's less restrictive -- especially at WOT as the vacuum inside the intake manifold is very slight and almost near ATM pressure.
There will always be more gas flow down the path of least resistance -- for instance, if the path between the valley cover and intake manifold was blocked or way too restrictive then you'd see a lot of oil back flowing down the fresh air tube and in to the throttle body.
If you're getting 98% of the PCV blow by in the catch can between the valley cover and intake manifold and none or super small amounts in the back flowing down the fresh air line, then it's not too restrictive.
Last edited by ZeeOSix; Dec 12, 2007 at 08:42 PM.
Race Director
Joined: Dec 2000
Posts: 19,304
Likes: 85
From: San Diego CA
You are correct in that vacuum pressure decreases as the revs are raised. Remember that the PCV valve acts as a check valve, preventing a reverse-flow situation, at least within the PCV line. Regarding blockage, you can simulate a severe blckage by pinching the hose in between the PCV and the intake. There will be a noticable drop in engine speed. I understand that many catch can designers take the conservative route and are happy to catch 50% of the oil. However, companies like Watts, Parker, and Wilkerson have been making "oil traps" for many, many years. It really isn't that easy to render their filter designs, useless, especially when your engine is circulating its synthetic oil through a high-quality filter.
Another thing to note is that GM is selling what is essentially, a flow-restricting oriface to replace the PCV valve in certain vehicles. Obviously, slowing flow is not all that bad......
Dave
Another thing to note is that GM is selling what is essentially, a flow-restricting oriface to replace the PCV valve in certain vehicles. Obviously, slowing flow is not all that bad......
Dave
Thread Starter
Team Owner
Joined: May 2004
Posts: 26,345
Likes: 232
From: SoCal
Well I got back from the track today.....
My can system in the PCV line was catching mostly water with some oil content.
My cans in the fresh air line were FULL!!!!!!!! with fresh oil out of the valve cover.!!!!!!!!!!!!!!!!!
This with with 30 minutes of severe track duty.
I was getting this same issue before when my coalsescing filter in the PCV line was new so I don't think its because of blockage.
Also putting flow restrictive push rods in didn't make a difference.
I don't think this engine has ring blowby like the last either.
I'm thinking the idea of a check valve in the fresh air line is necessary so that flow only allowed for air into cover not oil out......
DH
My can system in the PCV line was catching mostly water with some oil content.
My cans in the fresh air line were FULL!!!!!!!! with fresh oil out of the valve cover.!!!!!!!!!!!!!!!!!
This with with 30 minutes of severe track duty.
I was getting this same issue before when my coalsescing filter in the PCV line was new so I don't think its because of blockage.
Also putting flow restrictive push rods in didn't make a difference.
I don't think this engine has ring blowby like the last either.
I'm thinking the idea of a check valve in the fresh air line is necessary so that flow only allowed for air into cover not oil out......
DH
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
As the throttle valve opens wider and wider to WOT, the vacuum level inside the intake manifold becomes less, and approaches ATM pressure. At idle, when the throttle valve is fully closed is when the vacuum level is the highest, and when the PCV valve is restricting the crankcase gas flow the most. At WOT, the small spring in the PCV valve pushes the valve open more, and allows more crankcase gas flow through the system. If the engine backfires, or is force induction above ATM pressure then the PCV valve acts like a check valve and prevents higher than ATM pressure in the intake manifold to flow backwards in to the crankcase.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Other issue may be still too much oil in the top end and/or there is lack of sufficient oil baffling inside the valve covers where the fresh air line connects. Sounds like you need baffled covers or a baffled open breather setup.
Last edited by ZeeOSix; Dec 13, 2007 at 11:16 PM.
