I've been thinking about my setup lately and I must say I'm not really liking it. One of the important jobs of a PCV is to take contaminants out of the crankcase.
I got rid of mine because I was concerned about pressurising the crankcase with the supercharger. I think the reality is though, that with 5-6lbs of boost that just isn't going to happen. Even with a bit more boost it would be fine.
So right now, I'm just venting both rocker covers to the catch can, then have a filter on the catch can.
I'm thinking of using the setup in the image below:
So essentially still vent the crankcase to the catch can, move the breather/filter back to the crankcase and run a new line to the inlet manifold via a PCV/check valve, and also to the intake side of the supercharger with a check valve.
The theory is this:
- At idle and other times the engine is in vacuum, the PCV will open and create a vacuum in the catch can. The check valve in the supercharger line will be closed meaning that the crankcase should be ventilated.
- On boost, or at least non-vacuum periods the supercharger should continue to ventilate the crankcase by pulling air into it's intake, but via the catch can, so hopefully not too much crap will actually go through it.
- Even if the PCV leaks a bit, the supercharger should more than compensate for it to stop the crankcase pressurising.
I can keep an eye on the vent at the rear and if it's filling with oil, I don't have enough ventilation.
Any thoughts on a better way to do this?
Last edited by hybrid on Fri Jul 07, 2017 10:45 am; edited 1 time in total
You get better performance if there is a light vacuum in the crank case. Also better for the seals - less pressure / load on them so less leaks. Allowing the pressure just go out to air via a oil catch can is ok but not ideal.
The question is how do you get a vacuum. Normally from the engine itself via a PCV valve.
No good for a forced induction car. Best way is to have a Vacuum source, e.g., electric vacuum pump, mechanical vacuum pump or exhaust vac system. It looks like you have another approach using the intake tube as a vacuum source. I do not understand what the top line;s purpose is (then again I am tired so not working on all cylinders).
Yes the top line is hooked to the intake via a PCV like the original setup. It will create a low pressure in the catch can which should pull fumes out of the crank. Crank gets fresh air from breather as normal.
When there is no vacuum in the manifold, the supercharger should be pulling a vacuum via its intake, so it will take over the ventilation.
A page George sent me suggests using another check valve in the PCV line to stop ANY boost pressure getting to the catch can.
Using the arrows as an air pressure directional flow the lower is the vacuum source line. The short line is the feed to place the crank case in vacuum. The vent provides the air into the crank case so any oily crank case air gets caught in catch can. Now the top feed going into the crank case does not make sense to me especially when you have a vent.
Yes, the short line ventilates the crankcase based on the catch can being in vacuum.
Both lines with the arrows will provide vacuum at different times.
The top line does not go to the crankcase. It goes to the manifold below the throttle plates, to the location that the PCV would have been connected to originally.
So instead of the PCV being connected directly to the rocker cover, it connects to the catch can instead.
At idle, the PCV should have more vacuum on it than the supercharger inlet, so no crap will go through the supercharger.
I'm trying to avoid having ALL the crankcase ventilation done by the supercharger, but it can do the work when the PCV has no vacuum.
I just took apart my aftermarket rocker cover plug/PCV jobby and removed the PCV from it.
It seems very robust to me - all metal.
It seals as it should in one direction. I can't see why it couldn't easily handle 20 PSI - I could even test it with my compressor.
So I think I will configure this somehow to connect to the inlet manifold and I will use the old crankcase breather if I can find it.
Last edited by hybrid on Fri Jul 07, 2017 10:43 am; edited 1 time in total
OK but the top line is relying on only a PCV valve stopping boost - I would think it would not be good enough a one way valve. But you never know. If it is then all good.
I will test it with the compressor, but really... 5-6lbs boost?
Even if a little bit leaked past on boost, the inlet of the supercharger will be producing a lot of vacuum by then (thanks to air filter restriction), so it should more than compensate and keep the crankcase from being pressurised.
would be similar for the brake booster check valve. I received mix information that the standard check valve would not be suitable for boosted apps but the brake place suggested it was fine. I guess depends how much psi they are rated at, whether it was a quality one and how much psi you are expecting
'You can never test fire too many times.' - Hybrid
I will use the old crankcase breather if I can find it.
Look in the box on the shelf above the front fender ......
Just trying to be helpful (as I had nothing to add to the discussion) ...... 😄
Thank you kind sir
Yeah this is the thing. Factory turbo cars still have boosters... they still have PCV.
So there's got to be some way it works. My diesel challenger runs 20lbs boost from the factory. Pretty sure it's still running a vac booster.
I would be happy to just go back to PCV only to be honest, but reality is it's really only ventilating during periods of vacuum which even on a naturally aspirated engine is not when it's under high load. So now that I've got this catch can, why not try best of both worlds?
Last edited by hybrid on Wed Feb 08, 2017 10:51 pm; edited 1 time in total
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