hey
just wondering if the vent on the block is removable as i will be running 40mm webbers and haddent planned on hooking it to the manifold. are there any other options, i was hoping to just block it off with a welsh plug but im not sure if it needs to breath or not? will be to much pressure in the crank case if it is bloked?

cheers Dan

put breather outlet into catch can with small air filter so crank case can breath, it may create pressure being blocked off.

It needs to breathe. The rocker cover vent is for the top end. The bottom end needs to breathe too.

ok but in the case of say a 350 chev there is no ventilation for the bottom end... im stumped ????
cheers

Chevy 350 has larger holes between top and bottom ends.

Datsun A-series is designed to have the block vented top and bottom. The block tube is one, and the rocker cover vent is the other.

my L series has the bottom vent blocked off and just uses the top breather, it does have a big gap down the front of the engine where the cam chain goes so that it can tranfer pressure from bottom to top though

The reason there is two vents in teh A-series engine is to draw clean filtered air into the engine [via the rocker cover for conventional setup] and then pass any unburnt fumes into the intake manifold via the block breather. In the case of the GX induction setup the flow is in the opposite direction as the block breather connects to the air box and the rocker breather connects the inlet manifold.

If you are running twin webers, I would be inclinded to run both breathers to an oil catch can, as suggested by Bige.