Is one better than the other?I replaced the BG Demon Jr carb with a reman'd Autolite 4100,but it doesn't have a built - in vacuum port as the BG one did.I want to put a spacer on that was given to me that has a port,but it's open,not a four-hole type . I want to re-install the PCV on my 292 . I've heard the four hole type is better,some have said you'll only need to worry about it in a performance motor,which mine isn't . Also,would it be detrimental to leave the road draft tube on,while running the PCV system?

 

The open plenumn is ok for a non-performance engine - maybe some improvement if you're not a carb tuner.
With a PCV you are trying to pull vacumn from the oilpan up thru the manifold to reintroduce the vapors to the combustion chambers - leaving the draft tube on will short circuit the system.
(This answer is good until someone reads it or the batteries die)

 

Thanks,Dick.I am trying to stop marking my territory as much , it's embarrassing to leave that oil spot in others' driveways . I'm now being politely requested to park it on the street . One or the other , but not both, is what I had been told , but wanted to verify it .

 

The problem with the tube is that the vapors condence inside it - then it gets dust, dirt, etc and plugs up.
I think Albaturkey has a setup for PCV - Check his gallery.

 

I have a PCV set-up,but the road draft tube is presently installed.My(apparently mistaken) idea was to run both set-ups,hoping to reduce the amount of blow-by,and the ever-present oil spot.I think I now understand correctly that I should only have one of the two "systems" in place.But, like Sgt. Schultz says,"I know NOTHING."

 

Yes, PCV or road draft is an either/or thing. Air passing under the truck, past the draft tube opening creates a vacuum which pulls the crankcase vapors from out of the engine while you're driving. Not the most environmentally friendly approach, which is why it was replaced in the 1960's.

The closed, positive crankcase ventilation system draws that same vacuum but uses the engine itself as the source. That pulls the gasses back through the combustion process and burns them a bit more completely before sending them out the exhaust.

Incoming, makeup air for the crankcase for both systems comes in via the oil filler breather cap. Having a road draft tube in addition to PCV would be a place for dirty and dusty road air to be sucked into the engine. The large open tube would be the path of least resistance for the makeup air being drawn in by the PCV, bypassing the correct path with filtered air from the filler cap. I see that as a really bad thing, sucking in dirty air straight into the crankcase.

 

I think it does matter whether you use a 4-hole or not; depending what kind of carb you use, you don't want to confuse the pressure/vacuum signals the primaries see with the ones the secondaries see. I would think it will also induce some turbulence, that could upset flow.

I don't think my flatty PCV will do you any good; your 292 already had it, right? You just need a vacuum source that goes to both halves of the manifold. If the manifold is off (I'm guessing not?) you can drill and tap, but you do need to connect to both sides of the manifold.

 

I don't find any listings for "Albaturkey"

 

He meant me. What have you got?

 

Boys,it's Friday night,Lets' get it started!

 

Sorry,double post.

 

Ross knows I can't spell.

 

[quote=ALBUQ F-1;9166915]I think it does matter whether you use a 4-hole or not; depending what kind of carb you use, you don't want to confuse the pressure/vacuum signals the primaries see with the ones the secondaries see. I would think it will also induce some turbulence, that could upset flow. quote]

Agreed, although it wouldn't be too hard or labor intensive to try it out. 4 Hole Spacer Plates with a rear er... a.... orifice should be easy to find at a bone yard.

 

Tough day at the orifice dear? Sorry,too much caffeine today.I quit.

 

LOL....

You guys crack me up