crankcase ventilation

crankcase ventilation ,how does the upstream to the air cleaner and the downstream to the inlet manifold work when you have either triple choke weber carby set up or multiple throttle boddies like myself


I could put the larger hose from the breather on the rocker cover to the air box
But if I put the smaller down stream hose to one throttle body would it make that port oily or would the vacuum on that port be too inconsistant?

Chris,

I would suggest in your setup, that you abandon the manifold vacuum breather, and simply vent post oil-separator to atmosphere through a small K&N or similar canister filter. I imagine you are not excessively worried about venting the odd H-C here and there, as the vacuum take-off is mainly there for scavenge blow-by gasses and unburnt fuel (H-Cs) for environmentally friendly emissions. Provided the filter and feeder pipes from the oil-separator are not too small you won’t get any windage issues (high pressure built up by the crank high speed rotation).

Nice and easy.

I ran the engine for 2 years (about 15,000 km) with no breather tubes at all on the rocker cover and no fumes or oil residue came out of the oil canister on the rocker cover .
When I pulled off the rocker covers the inside of the engine was stained black ( I am using synthetic oil) when previously the engine was perfectly clean . I think it had one oil change during this time.

This is the reason why I may need the positive crankcase ventilation

Hi Chris,

Ok, shouldn't be a problem. Do you know what Air:Fuel ratio you are running? Is the engine running too rich on full power? May be getting some blow-by on worn rings / cylinder liners; can you measure the blow-by at idle and say 2k rpm in cfm? Can rig up an easy gauge with a welders bubble gas flow gauge.

I would try and avoid pulling the blow-by back in to save getting into detonation issues if you are running high compression and wild advance..
It's easy enough to do if you wish, just need a tapping into one of the runners post throttle plate, better if you can link up several this way.

You can also find one-way valves, used to be used on Fords, metal housing will withstand high temp, and use header extraction vacuum (mass flow past slash cut tube) to scavenge the crankcase - position just down stream of the 3-1 collector.

Just a thought.

Cheers,
Martin

Thanks Martin
the cams I was running had more than 10 deg difference in mop or lobe centers from left bank to the right bank so it was running a bit richer to balance the problem with the cams .
I have new cams now that Ferry Developement in France have gone back and fixed up their v6 atmo cam for me . They aquired an engine from Renault to re develop the cams on . I have just put them in and they degreed up exactly to their cam data that they supplied within a degree on mop . I will let you know how they perform once the engine is running again.

I have tapped into throttle bodies on cyl 3 and 6 to scavenge crankcase vacuum as well as the larger vac tube going to the air box

I am not exactly sure where or how you measure the blow by

thanks for your info Chris