PCV considerations

[Roger/Sacramento]

The down side to using a PCV valve is that along with the fuel-rich blow-by gases, oil vapors are trapped in the same spaces. This means that they both get sent back into the engine to be consumed with the regular air and fuel mixture. The oil can leave residue on the back of the valves and in the combustion chamber, inhibiting flow, and generally being dirty. Many engine builders use a catch can without a valve to allow free exchange of gases to the crankcase. These catch cans aren't as environmentally friendly, since the vapors are still released into the air they help but they help keep the engine clean.

Another option is to use PCV valves, but re-introduce the crankcase vapors into the exhaust, that way, the engine is not effected by the oil contamination. It's also common for builders to incorporate a vacuum pump. This literally pulls the blow-by gases out, and increases the pressure differential between the combustion chamber and the crankcase-the result being more horsepower to the wheels.

[JohnReb23]

bumping this up for interest.

i'm considering running a pcv to the exhaust and was wondering if there are anymore opinions about this out there. Any possible drawbacks? Would vacuum from the header be too much / not enough?

any input appreciated.

[Scott H]

What if you get a backfire in the exhaust, would that flame travel up to the crankcase?

[Flathead]

The PCV is a one way check valve, designed to prevent backflow to the crankcase.

[Ole Don]

The was talk the other day on the HAMB that a PCV caused carbon on the intake valves. I have worked on engines since long before PCV's were used. The valves look the same to me. The bottom line is, if you have a fresh engine that has been properly cleaned, and you like your engine to stay clean inside, use a PCV and it will be spic and span for years.

[36tbird]

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In my mind, the PCV system may work like the old Aamco top oiler kits to lubricate things a bit. Now, I'm sure that the top oilers using a bit of Marvel M.O. might be better.

Finally got the PCV system roughed in for my Eddie Meyer manifold I restored. This will be using the idea I got from Jack E/NJ to reverse the 59A flow direction of the crankcase ventilation system. The scoop/oil filler cap is just for looks and will be plugged and just removable for oil service.

[JohnReb23]

tbird, that's a beautiful setup. love the eddie meyer stuff.

[Flathead]

A PCV system should have a source of clean air entering the inside of engine and then a PCV valve connected to a central source of engine vacuum. Central being important so that all cylinders receive an even fuel mixture. The idea is to move clean air through the engine, removing blowby gasses and moisture, and keeping the interior of the engine happy and clean. The flow rate of the valve should be matched to the cid of the engine to avoid upsetting the air-fuel ratio. One drawback is that under load, when blowby will be the most, there is little or no manifold vacuum to operate the system. This is when that clean air source is needed to let the crankcase vent out. If a PCV is hooked up to an unvented crankcase it will cause problems as the system can't function properly. I don't think valve deposits are caused by a good PCV. Just something to consider.........

[blucar]

Positive Crankcase Ventilators (PVC) are probably one of the most misunderstood items ever installed on an engine. PCV's became mandatory on all vehicles built in 1963 and later, there-in the term smog motors was coined.
With the introduction of PVC's, 95% of the emissions generated by an engine were eliminated.
The PCV eliminated blow-by escaping into the atmosphere, while at the same time eliminating condensation within the engine. Introducing the blow-by back into the fuel mixture tends to act as an upper cylinder lubricant. It is also true that the fuel/air ratio needs to be leaned down a bit to offset the oil fume introduction into the engine.
I have figured out ways to adapt PCV's to every engine I own, or have owned for the past forty years. This adaptation has been on Ford Y blocks in my '56 & '57 T-Birds, my '59 Ford 100's w/292 Y blocks and my '36 Ford 59 AB engine.
On many of the cars I work on I am up grading the engine to a later engine so I use the PCV system that came on he engine.
I have found it to be very interesting that many mechanics insist on eliminating PCV's on early cars with later engines in them.

[DONUT]

Would you guys list the actual make and part numbers ofpcv valves that have been used on flatheads. I have a 1934 - 21 stud motor................thanks...............tp

[makemc]

Yes, I would like to know..Thanks

[36tbird]

From the HAMB, here are some bolt on ones, 1/4"NPT. I used the NAPA equivalent on my Eddie Meyer manifold. Note that these were the bolt on types that guys wanted to use under their manifolds to hide the PCV's. There is a picture floating around of a PCV set up using Toyota push in style PCV. I need the part number for that one if anyone has it.

[DONUT]

36tbird.................thank you !!............tp