Venting crank case to atmosphere vs under vaccum for boosted cars

[Allan-]

Ok well the standard system is under vaccum which helps with the emissions and obviously draws the oilly gas back into the inlet.
For turbo or super charged cars should you just vent to atmosphere (via a catch can or filter) or could you put in a 1 way valve and still run under vaccum?

 

[Fred@BTM]

Oil breather under vaccum? News to me, unless you class the stock intake as a vaccum!

 

[Allan-]

Well i assume when the throttle is down you get the suction from the engine drawing air in, else why would it have a pipe going to the intake?

 

[Fred@BTM]

Well vaccum is only truley created after the buttefly, catch tank is your friend

 

[Allan-]

What im trying to get at really is, should you retain the suction from the intake, or would venting into a catch can with no suction work fine on a boosted engine.
I was reading some posts about blow past at WOT saying that the vaccum / suction could help with keeping the presures down and avoid blow past on the rings.

But if the only real advantage is that it cuts down emssions but adds oily deposits back into the inlet then i think i can live with a breather or oil catch can

 

[MG cup]

Blank it, you don't want any excess pressure being fed back into the crankcase, vent the breather to atmosphere through a catch can or however you like.

 

[Dan519]

the small hole in the breather plate is there as a PCV (positive crankcase ventilation) so works in the way you've suggested. You should block this hole with boost or it is basically just a leak, and can pressurise the breather system under boost

 

[Chip-mk1]

Atmosphere every time for a boosted engine, the last thing you want is your octane rating getting lowered by oil in the intake charge.

If your rings are tired and its breathing heavily and you are worried about the tank filling up then return it to the sump instead, like we do on the group A cosworth engines (although a clio lump should NOT need this unless running ludicrous power).

 

[Allan-]

Ring's should be ok (12k since build) not getting any extra oil that i have noticed, it's running about 330 bhp just a breather filter atm i may have to invest in a catch can and actually keep a monitor of how much its breathing.
Any recomendations on what catch can to get ?

 

[Chip-mk1]

It really doesnt matter TBH mate, its just a put really, but the Mocul one is a nice bit of kit if you can stomach the pricetag.

I normally use those but on my turbo I didnt have a space that suited it so its ended up on an ebay cheapy I pinched off a car I scrapped which happened to be a good shape for it!

 

[Dan519]

Ring's should be ok (12k since build) not getting any extra oil that i have noticed, it's running about 330 bhp just a breather filter atm i may have to invest in a catch can and actually keep a monitor of how much its breathing.
Any recomendations on what catch can to get ?

get a tank with decent sized take-offs. the cheapest ones tend to have 8mm ones which are questionable and can cause pressure to back up. Ideally you want 12-16mm. Apart from that, it's just a container, but a sight glass is nice to have