wilch

Sorry if this is a silly question. But what exactly is an oil catch can for, how does it work, and why would I need one?

wil..

naishou

When a cylinder fires, some oil vapour, water vapour and other gunk is blown past the rings into the crankcase. In the old days this was vented to the air, but it's a pollutant. Nowadays legislation forces car makers to use Positive Crankcase Ventilation (PCV) which uses the pressure in the crankcase caused by blowby to redirect gases via a hose into the inlet, so they get burned again. The hose goes from the top of the valve cover to a place usually just after the throttle body. This is great if you have negative inlet pressure (inlet vacuum), but if you have a forced induction engine, you have a problem when under boost. To prevent inlet charge being blown into the crankcase, there is another connection (via a T-piece or similar) to a point before the turbo. Now when on boost the pressurised air will take this path instead and also create a little bit of vacuum in the part of the hose connected to the valve cover, helping to draw vapour out of the crankcase. The problem with this is that the oil vapour now goes through the intercooler and intake piping, condensing there. You can actually pour oil out of the intercooler on some high pressure turbo cars without a catch can. A catch can is a container that goes in the PCV line to filter and condense the vapour before it ends up in your intake. They are pretty much necessary on high pressure turbo engines, but on a NA engine the only point is to prevent the vapour getting into the cylinders again (it doesn't go into the intake hose on a NA car). This is bad because it reduces performance and effective fuel octane rating. However, unless it's got deliberately loose rings or is making a lot of power per litre, I don't think a NA car really needs one.

wilch

Cheers naishou

I was told I should think about installing one on the skyline when I get a larger front mount installed. I just had no idea what one did.

thanks again

wil..