Discussion in 'HYBRID -> ED-EF / DA' started by skellagher, Jan 19, 2011.
whats the purpose of the oil catch can?
While that's what it does-- it's PURPOSE to to stop detonation in the combustion process.
It's mostly needed for turbo apps, as the pcv runs on vacuum, not boost. Thus, there's effectively no pcv working when in boost.
Detonation caused by blowby otherwise being injested into the combustion chambers?
This really has nothing to do with blowby. That's a piston ring or other mechanical item problem.
PCV = postitive crankcase ventilation
as the the crankcase (ie, crank/oil pan area) spins, it's basically making an omelet... adding air into the oil to make it fluffy You end up with 'oily air'. This process creates pressure (think shaking a soda bottle) and the pressure needs to be released via the vacuum system. The PCV does it's best to SUCK just the air but leave these vapors in the oil pan to eventually settle back and split off into air/oil again. But's it's just a check valve more or less, and it simply doesn't function on boost, only vacuum. So, it's a wide open door when boosting. If theese vapors get into the main vac, it becomes part of the 'air' in the air/fuel mixture. These oily air molecules don't atomize well at all and basically mess up the combustion process. So, it's best to make sure these molecules don't end up there in the first place by maintaining a good PCV valve and catch can system if boosting.
This oily air eventually find's its way into the vacuum system
Blowby has everything to do with Positive Crankcase Pressure. The more explosion pressure in the cylinder, the more blowby. As such, a boosted engine will produce more blowby than a NA setup.
Blowby from piston/rings and valve seals/guides is the source where positive crankcase pressure comes from.
PCV = Positive (as in positive air pressure or crankcase pressure) Crankcase Ventilation. Eliminate the blowby (impossible to do) and there is nothing to ventilate.
PVC is designed to recirculate positive crankcase gasses ( to include suspended oil particles and burned and unburned fuel) back through the engine via combustion chambers to keep it from venting into the atmosphere - hence causing more pollution.
When connected to a NA intake manifold the PCV valve sees vacuum - on a boosted engine it does not.
Thanks for the description and awareness.
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