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Old 07-27-2017, 10:45 PM
theultimatehero theultimatehero is online now
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Default Do I have a blowby problem? Redtop SR20DET

I had this discussion in my build thread probably a year or so ago and now it is something I need to address again.

I used to have my crankcase ventilation set up traditionally:

Crankcase > Valve cover > catch can > turbo inlet

I have a really ****ty catch can with no baffling. When set up as above, oil would end up going through the catch can, through the turbo, and absolutely coating my intercooler/intake. I decided to be lazy and cheap so instead of buying (or making) a nice baffled catch can I decided to remove the line going to the inlet of the turbo and just run a vent on the catch can. The new system looked like:

Crankcase > Valve cover > catch can > Vent

I drove it like that for a while and it has been tolerable. Instead of having oil leaking out of my intercooler, I now have to empty the catch can often. But, it seems at this point I am emptying the catch can REALLY often.

I find the engine consumes about a half quart of oil per tank of gas for normal driving and if I'm pushing hard it's probably more like a quart per tank. It also fills my catch can (maybe 750ml?, not sure) in similar intervals, maybe a little slower.

I'm trying to decide what I should do. I want to buy or build a baffled catch can because the vented one is spewing oil all over the engine bay, but I know it's going to be filling up just as fast if not faster (considering I would reconnect the line to the turbo). I'm wondering if I have a serious blowby issue here, or if this is somewhat normal. Should I be thinking about doing a rebuild on this engine?
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Old 07-28-2017, 05:48 AM
maxtherabbit maxtherabbit is online now
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time for rings...
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Old 07-28-2017, 05:57 AM
Matt93SE Matt93SE is online now
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Run a hose into the bottom of your catch can, not just the side.. and make sure there's a filter on the vent. under no-load conditions, there *should* be a slight vacuum in that line. If you run the hose to the bottom of the catch can, it'll fill up the can under heavy throttle and then suck it back into the engine under low load conditions when there's vacuum on the lines.

I did that to my NA KA about 10 years ago, and have had add any oil between changes...
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Old 07-30-2017, 12:06 AM
theultimatehero theultimatehero is online now
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Quote:
Originally Posted by maxtherabbit View Post
time for rings...
That's my fear

Quote:
Originally Posted by Matt93SE View Post
Run a hose into the bottom of your catch can, not just the side.. and make sure there's a filter on the vent. under no-load conditions, there *should* be a slight vacuum in that line. If you run the hose to the bottom of the catch can, it'll fill up the can under heavy throttle and then suck it back into the engine under low load conditions when there's vacuum on the lines.

I did that to my NA KA about 10 years ago, and have had add any oil between changes...
Interesting, I hadn't thought about trying to suck the oil back out of the can! So you would suggest leaving it the way I have it, but adding another line that goes from the bottom of the catch can back into the crank case? Not sure how I would do that, but it's quite possible.
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Old 07-30-2017, 11:15 PM
jfryjfry jfryjfry is offline
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He isn't saying run a new line but have the hose from the valve cover go into the bottom of the can. When you shut the car off, the oil will drain back down. If your pcv system is hooked up and working, it might pull some back in under high vacuum situations (off throttle).
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Old 07-31-2017, 05:55 AM
Matt93SE Matt93SE is online now
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As jfryjfry said, just extend the hose inside the catch can from the fitting on the side down to the bottom of the can. the catch can I bought had an AN fitting screwed into the side, I just pulled it out and replaced it with a bulkhead fitting so there was another fitting on the inside. I then poked another short section of hose down to the bottom of the can from that fitting.

Now, when you're off the throttle and there's a slight vacuum on the valve cover breather vent.. that vacuum just sucks the oil back into the top of the head and voila.

That said, if you truly have a problem with blowby this is only a bandaid on the problem.. it's not going to fix broken or worn rings, but it will at least stop overflowing your catch can every day.
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