ninety15.0 said:
thats confusing man...i dont think you know what the word via means. Secondly EFI stangs as im sure u know have only one pcv in the lower and nothin on one valve cover. Please explain to me how crankcase pressure equalizes internally as quickly as it appears if only one VC has a vent hose. Given the physical properties of the venturi effect (which is the principle on which the stock VC to TB vent is based) the air would be sucked out of the valvetrain so fast at WOT and so incredibly slow at any other part throttle application that it would be negligable (like being vented to atmosphere)...im therefore lead to believe that on a stockish 5.0 there just isnt enough pressure, or lack there of, to cause a problem with a filtered breather. plus why wouldnt all of us that do run breather/filters have longevity issues?
I feel your pain, as this is still somewhat confusing to me.
Here is what I know from troubleshooting my own pcv system. The engine vac signal is much stronger at the pcv (from the inside of the intake) compared to at the TB (outside the intake system). This is why air is usually not pulled out of the VC, but does travel through the PCV. Most often it is a 1-way system. The venturi effect is not really how the TB/VC line works, although it does increase the efficiency of the system. The primary driving force is the engine vac signal at the pcv. Also, keep in mind that pressure is not strongly dependent on flow. Pressure in the crankcase can change a great deal with only minimal flow, and it can decrease as quickly as it increases.
"What we have here is a failure to communicate!"
It sounds like ninety15.0 and 18mustangs are talking about 2 different systems.
The issue that is being discussed is whether or not an open element breather cap can be used on a pcv equipped car. The function of the pcv has been very well described in above posts so I will leave it alone here.
car 1
5.0 mustang with pcv and open element breather.
There will be fresh air pulled through the open breather, into the crankcase, past the PCV, and into the intake. None of this air is metered at the MAF, and none of this air is throttled at the TB. This will cause drivability issues, very similar to a vac leak. Things get even worse with stronger vac signals, which pulls more oil from the crankcase, fouling plugs and CC's.
car 2
Same car with pcv and VC/TB hose (no open element breather).
Air is now pulled from just before the TB and follows the same path, through the crankcase, pcv, then intake. The difference here is that the air flowing past the pcv in this scenario has been metered at the MAF, even if it is still not throttled at the TB.
my thoughts
jason