mcdarrunt

Straight 8 PCV pics

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Anyone have any photos of a SUCCESSFUL pcv setup on a straight eight? Object of a pcv system is to keep engine under a negative pressure so am wondering if it would work to put the pvc valve in the rocker cover and a filter on the road draft tube to prevent dirt ingestion. This seems to be the easiest approach and since not much free oil is around the rockers a baffle may not be needed. Thank you

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Benefits of AACA Membership.

The first Chevrolet "closed" systems was a cone-shaped metal piece with a bolt holding it in (where the prior draft tube would stick into the rear of the engine block).  It had a 3/8" fitting on it, which went to an inline pcv valve, which then went to the rear base of the carb.  As most road draft tubes were somewhat universal in their mounting method, that might work there, too.  1967 vintage Chevy V-8s, probably in some of the Corvette restoration catalogs?

 

The reason for the ventilation system for the crankcase is to reduce condensate accumulation in the crankcase.  Especially if the vehicle is used for a lot of slow driving.  Back in the 1970s, one of my "cheap entertainment" activities was to go to the Texas Tech University library, where I'd found their "stash" of S.A.E. TRANSATIONS books.  MANY interesting things in them!!  One I happened across was a GM paper on crankcase ventilation systems and their effectiveness in internal sludge accumulation.  Their test vehicles?  Two 1961 Chevy 6-cyl sedans which were used by their plant security department.  All slow-speed driving on the plant grounds.  ONE valve with a specific slow rate made a big difference, with an additional one making more difference in sludge accumulation within the motor, but the second one was not as significant as the first one was.  So only one was deemed necessary in a cost/benefit analysis.

 

Placement of the pcv valve should also take into account crankshaft windage within the crankcase.  Placing the valve such that such windage helps things along rather than otherwise.  Keep a filtered oil fill cap on top, then remove the draft tube and possibly seal the bottom, placing the valve inside a rubber grommet and running the tube to an inline valve on its way to the carb's base, into a passage that goes to the bottom of the throttle bores, below the throttle plates, as all modern carb pcv passages do.  Almost all of the 1970s pcv valves have similar flow rates regardless of the size of the engine.  If the right angle plastic piece on the valve is not needed, it can be removed to reveal a straight nipple to which a vacuum line can be attached.

 

For that "factory experimental" look, you can get one of the vapor separators from a modern 4-cyl engine and hook the pcv valve to the outlet side of it.  With the inlet side letting any accumulated motor oil drain back into the crankcase via the former draft tube's location.  The first vapor separators were used on the original Oldsmobile Quad4 engines, which also included a heating element in that item.  There was no pcv valve as the system ran with a fixed-orifice fitting into the intake tract, rather than the variable-flow pcv valve we're used to seeing.

 

End result, you want filtered air coming into the engine (usually with a filler cap with the hogs' hair filter) and the crankcase "air" exiting for recycling into the base of the carb.  Might need to up-size the carb main jets by .one or two sizes to compensate for the additional air flow, as needed.

 

Enjoy!

NTX5467

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The important thing is to arrange the pcv inlet so that the air mixes with the air/fuel coming from the idle jet, and don"t have too much flow for the engine size.

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I will first give Ben's suggestion a try which was the first way I considered but rejected because there seems to be some liquid oil droplets in the draft tube which would result in exhaust smoke and possibly increased oil consumption. The line from the draft tube to the carb base will also be longer than most suction lines. I could also put baffles in line or maybe a vapor condenser can like sbc had under the intake. Will update with results.

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