My concern with any crank vent check valve, whether it be a PCV valve or a pollution control valve is that they appear to be a spring load disc, which I have heard more or less "floats" when the pulse reach 9000 RPM which is 150 pulses per second (even on a 4 stroke). I'm pretty sure the auto manufacturers were not concerned with them working at those RPM's, as I doubt that the environmental tests required that. The reed valve ones, made using reed valves designed to control intake pulses on 2 stroke engines are supposed to work at high RPM's. If they float or flutter at my max hp RPM, which is somewhere around 8300 RPM, none of them will help max hp. That is why I think the exhaust extractor would be superior, as I would think the venturi effect vacuum signal would continue to increase as the exhaust velocity increases. The check valve then only comes into effect on a backfire which might allow a flame front to travel backwards into the cases. If I can get the exhaust extractor to work, the check valve operation may become less important, as it may simply stay open until that backfire happens. I have no desire to experience the results of the "big bang" theory first hand!
The Krank Vent system claims to "maintain a constant vacuum of -5 to -7 psi". That's not helpful on the up stroke. To be totally useful you would have to provide vacuum on the down stroke and pressure on the up stroke.
Yes, we have that problem with reciprocating motors. A long cylinder with a piston at each end like a steam engine might work, but I'm sure someone has tried that. One way to mitigate the crankcase pressure problem is simply to make a large enough breather hole that the air can travel in and out with little resistance. Thinking a hole the size of my piston. Preferably the hole is there and the motor is still running!
Tom,
I once helped install the Moroso part you linked to on a turbo drag car. My understanding of the slash cut in the exhaust is that it helps to create a localized low pressure on that end of the extractor pipe from the exhaust stream passing over it. The pressure differential helps evacuate your crank case. I have seen home made media blasting set ups that use the same principle.
A reed valve might be a good solution on a bike due to space constraints. There are 2 stroke snowmobile engines that run up past 8000 RPM on reed valves. I would imagine that means you could source something that would keep up with a 9000 RPM 4 stroke.
It would be very interesting to see back to back dyno runs with and without the evacuation system in place.
Looking at the installation instructions for the Moroso unit, the slash cut end lies almost flush against the pipe wall. Can't see how that creates any pressure drop. The bird's beak opening is upstream, so my guess is the flow of the exhaust thru this small opening is what causes the lower pressure at the slash cut opening. But since the Summit Racing one doesn't seem to have this feature, I wonder if it's just another case of " smoke and mirrors". I'm going to try some different designs using a shop vac, some plastic "exhaust pipe", different extractor shapes, and a manometer to see if one way pulls more vacuum than another.
Tom