When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
TLDR: Vent off the front of the block to reduce the amount of oil getting pushed into the catch can. This allows the head to drain better.
I've come to the opinion that when your catch can is filling up, it's a symptom of the head not draining effectively.
The head doesn't drain effectively when there is too much crankcase blowby flowing up the head oil drains.
So when we vent off the block directly, it reduces the amount of air that needs to travel up into the rocker cover and then out the rocker cover (valve cover) vents.
When you reduce the amount of air travelling up the oil drains, the drains can function more effectively. This keeps more oil in the pan also and I noticed less oil surge at my last track day.
My catch can used to fill up in around 3 laps. Probably 1000ml or so.
With the new setup, I did 7 hard laps and it had ~100ml in the catch can. Now I dont have oil everywhere in the engine bay!
My 12AN vent of the block surely flows more than the OEM factory ports on the rocker cover. My next track day I will try this vent only with the other two rocker cover ports being blocked off.
12AN (1/2NPT base) fitting installed into the front balance shaft tunnel. Installing onto the front of the block is critical because the oil is already flung onto the back of the block. The front of the block should be relatively "dry".
Inside shot. I drilled this in place with the engine assembled. I just removed the oil pan and baffle/windage trays.
Grease does wonders for catching swarf. There is a rag on the inside covered in grease also to stop the spread.
12AN line fitted to the new fitting with heat proof sleeving for thermal protection.
New catch can with 3x 12AN ports, 10AN drain and 4AN drain. The 4AN drain hooks into the front balance shaft inspection hole port for passive draining (when the car is off). This drains *really* slow.
New engine bay setup. 3x 12AN lines going to the catch can. Battery is on the front-left chassis rail (in front of the front left wheel), so there is plenty of room.
Hose routing pic
Bullet in Australia puts what looks like a massive 16AN or 20AN orb fitting in the same place. They actually recommend venting here for dry-sump systems also.
all 3x AN12 lines are connected. 1st/2nd gear pull. Approx 3.5kpa pressure rise (only 0.51psi). Pressure is measured in the block (not in the head).
Block 1x AN12 line connected only. 1st/2nd gear pull. Approx 4.5kpa pressure rise (only 0.65psi). I wanted to check if the block only breather would be good enough for trackday use.
We all like data but I don't recommend blocking the valve cover ports off. The engine needs to be able to move any crankcase pressure . You don't want it pushing out other areas and creating oil leaks.
We all like data but I don't recommend blocking the valve cover ports off. The engine needs to be able to move any crankcase pressure . You don't want it pushing out other areas and creating oil leaks.
Both valve cover ports are blocked off, but i've still got the 12AN breather port off the block.
So it's got 1x 12AN line for breathing.
Another simplier option for block breathing could be to enlarge the balance shaft inspection bolt hole.
This is a M10 thread.
It could be enlarged to M16, maybe even M18.
Much less "scary" that drilling a hole into the front of the block. Will just need to make sure it clears the turbo OK.
You might get a lot of oil up that line, because it's on the back of the block and that's where the oil gets flicked up.
Breathing off the front stops that.
You might get a lot of oil up that line, because it's on the back of the block and that's where the oil gets flicked up.
Breathing off the front stops that.
The adapter is perpendicular and isn't in direct exposure to oil splash and then the ORB 90* fitting, then the 90* hose end has 180* of direction change so I figure that would prevent oil from getting pushed through the line.
Mike have you tried putting a pressure sensor in one of the blocked ports on the cam cover to see what it’s like between fully blocked off and 1 vent? Be interesting to see if you need to it blocked to draw the oil down, or if a bit of venting helps it flow down a bit.
Here ya go.
I recently pulled the motor and noticed there was oil in the intercooler piping and intake manifold.
I haven't checked that for a while, but it's never done that before. I'm assuming it's because i've blocked off the rocker cover breather ports and was running off the block only.
So at this stage I wouldn't recommend blocking off the rocker cover ports like I had done for testing.
But I still extremely highly recommend breathing off the block, It solved my catch can filling up, and the theory behind it is sound.
