I've been thinking about how I want to run my crank vent system once I supercharge it, and I want to ask a question with your setup hybrid.
If I was to delete that line completely that goes from the intake manifold to the catch can, would it still work?
In my thinking(which is most likely wrong), under idle/no boost, there will be vacuum in the manifold, which means it will be drawing fumes in via the intake system. Under boost, the supercharger will create a vacuum, drawing fumes in again via that same line.
Is there really a need for the intake manifold to catchcan line?
1) There would not be enough vacuum created in front of the supercharger at idle to pull any fumes out unless you had a really restrictive filter (which you obviously dont want).
2) There is a bypass valve (AKA blow off in the turbo world) between the supercharger and manifold which is wide open at idle and light throttle (pulled open by vacuum). Any fumes pulled in via that front line would be blown back into the atmosphere while that valve is open. It could get a bit stinky and smokey potentially.
3) If you only use one of the lines, you can only pull the fumes during vacuum OR boost, not both.
My setup provides draw from the crankcase theoretically all the time. The one way (check) valves I put in each line makes sure air can only go in one direction, and only air from the crankcase will be pulled.
When I didn't have any crankcase vacuum - just breathers on each rocker cover going to the catch can, I actually had slight oil leaks around the sump.
Once I put this system in, no sign of it again. It seems to be a common theme.
Edit: one other thing I forgot about. I didn't want to suck too much crap through the supercharger, so the PCV should do the vast majority of the work.
Yep that would work.
Notice in his update though, he's switched to using PCV for normal driving, and now switches the electric pump on during wide open throttle.
I'm not a fan of replacing mechanical stuff with electric generally, but it's definitely another option.
It doesn't return the fumes to the engine for burning either.
For a mafless setup, do you think this would work with the normal run of the mill 2 port catch cans, which is what I have. The blue arrows are check valves. I think it's similar to your setup but using only two ports instead of three.
Under manifold vacuum, the check valve in the line to the intake will shut. Once you're on boost, the manifold check valve will shut due to boost, and all the fumes will now go via the intake.
Last edited by Husky65 on Wed Aug 02, 2017 3:26 pm; edited 1 time in total
Yeah that should work in a similar way to mine, as long as there is enough vacuum from the supercharger intake to pull open the PCV.
If you have a very good flowing filter, your vacuum in front of the supercharger may not be all that high, but give it a shot.
At the very least, you will still be pulling fumes out of the crankcase under general driving conditions.
Edit: By the way, I can modify your catch can easily enough if you want to add an extra port. Or, if you could get hold of an inline PCV, you could run a non-pcv valve cover breather and move the PCV into the line going to your manifold. That way, manifold vacuum will still open the PCV, but the supercharger can pull fumes much easier when you're on boost.
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