Reed valve; breather?

[WMarshy]

The valve actually is designed to allow a certain amount of vacuum to be applied to the crankcase instead of the crankcase being vented to air. The valve by itself would from what I know of their operation actually increase the pressure in the crankcase with no vacuum applied to the other side. Here is a wikipedia article on the device.

I think it explains things reasonably well.

Exactly what Im trying to explain, just putting on a PCV and allowing it to exhaust to atmosphere will not generate a negative pressure in the crank case, if anything it will generat a greater pressure due to the restriction of it. To get a lower than atmosphere pressure the outlet of the pcv needs to be lower than atmosphere... ie. hooked to the intake plenum.

[slow mo]

K Nfilter

i went to the local auto parts store and bought a KN filter with ,a 1/2 in port,, i,m not positive on the size but i think i,m right ,,good luck ,,ride safe ,,slow mo!

[dbeardslee]

Whether it's applying vacuum to one end of the valve, or pressure to the other side they both have the same affect on the valve - they both open it. Why would a system with a PCV valve even need the valve if it's never going to close?

[WMarshy]

Whether it's applying vacuum to one end of the valve, or pressure to the other side they both have the same affect on the valve - they both open it. Why would a system with a PCV valve even need the valve if it's never going to close?

Yes, in both situations the valve would open, I'm not disputing that. I am disputing the conditions in which a negative pressure would be created within the crank case. By venting the pcv to atmosphere I don't think its possible for a negative pressure to develop. The volume inside the crank case remains constant, for all intensive purposes the temperature remains the same or increases, and the blow by the pistons would be the only increase in the pressure to the system... The pcv would close (if connected properly to the intake plenum) when/if there was a backfire, or anytime the pressure on the outlet side was greater than the inlet side.

[NYPD]

PCV= Positive Crankcase ventilation...Not negative...end of argument

[cywelchjr]

PCV= Positive Crankcase ventilation...Not negative...end of argument

That argument holds no water. Positive Crankcase Ventilation is a system, of which the valve is one part. Provided that you have a filtered inlet, and have the valve connected to a vacuum source then yes, you will have positive ventilation, meaning air will be drawn through the crankcase, and you won't actually have a vacuum in there because air is pulled through by the vacuum. If you connect it to a closed system that has no input AND connect the valve to a vacuum source, then you would get a vacuum, but that would mean among other things no blowby and no other ways for air to get into the crankcase. There are scavenging systems that do actually pull a vacuum on the crankcase, but the PCV system does not do this. And it's probably the WORST thing you can do to one of these bike to put it on there, as it will increase the pressure in the crankcase and prevent gases from escaping as well. If you look at the stock airbox, you will see that it does have a primitive scavenging system , as the line the vent hooks too splits into 4 lines and points into the velocity stacks, and when air gets moving through them there will be a SMALL amount of suction applied to the pipes. If you run pods, just put a filter on there and make sure it stays clean and clear, if you want to put a PCV on there, hook it to one of the carb vacuum nipples and you might get the result your looking for, but then you might just get a lean cylinder too.