Positive Crank Case Pressure

I put a PCV valve on there and a secondary vent on my oil fill cap . .. I hooked the PCV to the oil seperator . . .same place the stock hose was that went to the air cleaner to just vent . .. doesn't pull any oil out of it from what I can tell . .. the secondary vent I think is important 'cause I could feel a vacum on the oil fill cap . .. when I was a kid I had a Mustang that didn't have a breather but had a PCV and it kept sucking the end intake manifold gaskets in . . . . all the research I did led me to believe more venting can never be a bad thing unless you're doing dry sump and trying to pull a vacum . . . actually maybe it is good to let the PCV pull vacum??? only thing that bothered me is at WOT you're not pulling any vacum so I think you want some secondary vent 'cause this is when you really need the evacuation.

just my experiences with it .. I asked about it a year or so back when I did it and no one responded.

cheers,

Sean

 

In the stock configuration, the blowby gasses and any oil spin around in the separator to remove oil and the gas leaves from there. Nothing wrong with that. The PCV system is supposed to flush the crank case with 'fresh air', and is a 'green' device. Even if you were interested in cleaning up the environment, I doubt it would work on a 308 as the crank case is going to be positive most of the time and manifold vacuum to drive the system is miniscule.

 

that's a good point on Kjet cars . .. I noticed when I did my EFI conversion the manifold vacum at idle went way up . .. I think PAD has some EFI conversion so he might have decent vacum . .. the other thing you can do which I asked about was install a vacum pump.

 

I thought about just putting a bunch of little K&N's on all the factory vent pipes . .. one on the crank vent and two on the cam cover vents plus you can vent the oil filler cap and if you ditch the dizzy's make vents out of them too

 

I believe some NHRA Drag engines are designed with a pump to provide a vacuum in the crankcase in the interest of performance. Perhaps to promote oil delivery through the system. I read somewhere that F1 may use something similar but I'm not sure. I do know that F1 cars have to vent the crankcase to the air intake:

 

The only way I can think that you built up blow the dip stick out crankcase pressure is if the vent became completely blocked....I've had it happen on a bike and blowing out the dip stick was the result.

Is it possible you got oil trapped up in the seperator tank I think I see? That would cause ecrankcase pressure and spray oil out the vent line I think.

 

We used to fit pan evacuation systems to drag cars. These were simply a hose connected to the valve cover fitting - used one on each cover - and then plumbed to a checkvalve/fitting in each header collector with the tube into the collector welded in at a 45 degree angle. This generated considerable negative pressure in the crankcase and was good for around 10HP at WOT. There was so much neg pressure that when you shut the engine off you could hear "hissing" for several seconds as the pressure equalized. THe check valve was to prevent any damage from a backfire within the exhaust system.

 

Some books on F1 engines I read explained how Honda discovered some serious power (8-10 hp? ) in the early 90's pulling heavy vacum with the scavenge pumps . . it's one of the benefits of a dry sump system period isn't it?

 

It sound like you're on the right track to me (sorry about the pun )

 

"We used to fit pan evacuation systems to drag cars. These were simply a hose connected to the valve cover fitting - used one on each cover - and then plumbed to a checkvalve/fitting in each header collector with the tube into the collector welded in at a 45 degree angle. This generated considerable negative pressure in the crankcase and was good for around 10HP at WOT. There was so much neg pressure that when you shut the engine off you could hear "hissing" for several seconds as the pressure equalized. THe check valve was to prevent any damage from a backfire within the exhaust system,."

The PCV system in my 78 308 is very similar to this. we used a one way valve at the collector, plumbed in to the oil separator with a restrictor in the line. this setup works great. for example, instead of using the hose that goes to the air filter, that hose now goes to a one way check valve in the exhaust collector to help create neg pressure in the crankcase. the restrictor i made - just a wooden dowell with a hole thru it - without the restrictor there was way too much suction. the stock oil separator and return line to the engine are still being used.