N/A Crankcase Ventilation
01-17-22, 11:52 AM
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N/A Crankcase Ventilation
After reading through some old threads, I have some questions. Proper crankcase ventilation to a catch can seems to work best for Turbo engines.
My most recent FC (86 NA) came as a basket case with missing pieces, so the stock setup was not an option. Both the Oil Filler port and the Center Iron port were plugged by a previous owner, but I figure it at least needs an atmospheric vent.
Currently I have the lower nipple on the center iron connected to a vent hose with a generic PCV valve inline. I have this hose connected to manifold vacuum.
The top nipple on the filler neck is plugged at this time.
The idea is that the intake manifold connection will pull a slight vacuum on the crankcase, which will be limited by the PCV valve.
I feel it would be best to have the upper nipple open vented with a filter.
Anyone have a better recommendation or improvement to this setup?
My most recent FC (86 NA) came as a basket case with missing pieces, so the stock setup was not an option. Both the Oil Filler port and the Center Iron port were plugged by a previous owner, but I figure it at least needs an atmospheric vent.
Currently I have the lower nipple on the center iron connected to a vent hose with a generic PCV valve inline. I have this hose connected to manifold vacuum.
The top nipple on the filler neck is plugged at this time.
The idea is that the intake manifold connection will pull a slight vacuum on the crankcase, which will be limited by the PCV valve.
I feel it would be best to have the upper nipple open vented with a filter.
Anyone have a better recommendation or improvement to this setup?
01-17-22, 03:04 PM
#2
Rotary Freak
Your setup as described will cause a vacuum leak at low rpm. Without the oil filler neck vented it won't cause a vacuum leak, but also won't be as effective as stock.
The stock system works really well. I think Aaron explained it in an old thread, but basically air is drawn into the crankcase through the lower barb, circulated around the crankcase to grab the vapours, then sucked into the engine through the upper barb and PCV valve when the engine is above 2000rpm. A small vacuum line on the PCV valve supplies the vacuum signal for the PCV valve to open up at the appropriate rpm.
At idle the valve is closed so there is no vacuum leak. At 2000rpm and above the ECU is tuned around the air being inhaled (either that or it isn't significant, not sure which).
IMO the best way is to tee into the stock system. Putting a sealed catch can inline between the PCV valve and UIM. This should preserve the air flow and also let you catch anything before it's burned. If I find the old thread I will link it. I think there was a diagram provided.
Since you don't have the stock system, I just used a vented catch can with two inlets for awhile (one inlet to the center iron barb, one to the oil filler neck barb). It didn't cause any real issues but I did notice two things:
- My 3800rpm hesitation was worse (likely unrelated) with the catch can set up as above.
- Nothing appeared in the catch can. Either I have very low blowby or this system isn't as effective as the stock one. Probably both.
So if possible I would get an OEM PCV valve from the dealer and use that. The OEM setup is as follows:
- One line from hardline on firewall that comes from charcoal canister to the center iron barb.
- Short line from the oil filler barb to the bottom of the PCB valve.
- Short line from the PCV valve to the barb on the dynamic chamber, below the BAC valve.
- Thinner vacuum line from the small barb on the bottom of the PCV valve to the back of the dynamic chamber (I think it's the lower nipple, but the Factory Service Manual shows you which one).
The stock system works really well. I think Aaron explained it in an old thread, but basically air is drawn into the crankcase through the lower barb, circulated around the crankcase to grab the vapours, then sucked into the engine through the upper barb and PCV valve when the engine is above 2000rpm. A small vacuum line on the PCV valve supplies the vacuum signal for the PCV valve to open up at the appropriate rpm.
At idle the valve is closed so there is no vacuum leak. At 2000rpm and above the ECU is tuned around the air being inhaled (either that or it isn't significant, not sure which).
IMO the best way is to tee into the stock system. Putting a sealed catch can inline between the PCV valve and UIM. This should preserve the air flow and also let you catch anything before it's burned. If I find the old thread I will link it. I think there was a diagram provided.
Since you don't have the stock system, I just used a vented catch can with two inlets for awhile (one inlet to the center iron barb, one to the oil filler neck barb). It didn't cause any real issues but I did notice two things:
- My 3800rpm hesitation was worse (likely unrelated) with the catch can set up as above.
- Nothing appeared in the catch can. Either I have very low blowby or this system isn't as effective as the stock one. Probably both.
So if possible I would get an OEM PCV valve from the dealer and use that. The OEM setup is as follows:
- One line from hardline on firewall that comes from charcoal canister to the center iron barb.
- Short line from the oil filler barb to the bottom of the PCB valve.
- Short line from the PCV valve to the barb on the dynamic chamber, below the BAC valve.
- Thinner vacuum line from the small barb on the bottom of the PCV valve to the back of the dynamic chamber (I think it's the lower nipple, but the Factory Service Manual shows you which one).
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