pcv system

[msmith10]

Is there sufficient vacuum at the manifold connection for the carburetor fuel scavenger tube to tee off of this and connect a pcv valve to the tee? This would avoid the carburetor spacer plate as in the Indigo system and would be dirt cheap. I have to think this doesn't work or everyone would have done it by now.

[Dave Neptune]

Mark, it would not be a good place to mount the valve. The plate is used so the gasses from the crankcase are "mixed" with the incoming fuel for an even distribution throughout the intake manifold. Virtually all applications of a PCV are done in this fashion.

Dave Neptune

[lat 64]

I made my own pvc, and teed it to the scavenge tube, but I do not recommend this. I have no way to know if I'm burning a valve or not.

It works, but Dave is probably right. I think I will make a plate and run the vent line to that. I think a plate will pass more volume too.


Russ

PS: I think it makes sense to put the inlet upstream of the venturi. Maybe another fitting in the air horn.

[hanleyclifford]

Another thing to consider when installing a pcv system: plug the oil breather with a npt plug and use for adding oil only. The breather tube to manifold link via the pcv valve will ensure negative crankcase pressure and the plug will minimize the vacuum leak.

[Dave Neptune]

Hanley, you need to have an open vent to the crankcase for things to work properly. The PCV valve puts a constant draw on the crankcase and fresh air should be flowing into the crankcase at the same time. I have seen cases where the vent was plugged and it sucked the silicone out of the valve covers resulting in a major mess.
The crankcase must be ventilated or you could have explosive results internally if you get a bit of fuel vapor in the crankcase!

Dave Neptune

[hanleyclifford]

I disagree. There are sufficient other small leaks to allow some influx into the crankcase. The premium in my opinion is on keeping the crankcase at low negative pressure, dealing with any blowby from the cylinders while minimizing the vacuum leak which the pcv system certainly is. BTW, I do not have a mechanical fuel pump but if I did that might cause some concern.

[lat 64]

Thinking about this just now it seems that if you get lower pressures in the crankcase, then you exacerbate blowby.

I researched this for myself last year and found that over the years auto manufactures tried all this tuff. Volvo reversed or changed the flow several times trying to get the least troublesome system. In auto engines they want more flow for emissions and moisture evacuation. In large(ships and trains )they want less air(oxegen) to avoid explosion. 67 c&c knows more I think.

Different strokes for different blokes

[Al Schober]

You'll be doing well if you can get the crankcase pressure below ambient! There's a huge air leak around the fwd end of the crankshaft. Plugging the oil filler isn't going to change that!