C2- PCV?

[john pickens]

My C2 roadster has a 327/350 original engine with AC and 4 speed trans. I have
reviewed assembly manual and various references and vendor catalogs. Still not
sure if this engine has a PCV valve or simply a hose from oil fill to carb or intake. Any assistance appreciated.

[William C.]

Re: C2- PCV?

What year?, systems changed significantly in some years.

[Duke W.]

Re: C2- PCV?

What year?

All C2 PCV systems have BOTH inlet and outlet circuits, but not all have valves.

Duke

[john pickens]

Re: C2- PCV?

Sorry thought I mentioned the car is a 65. Thanks.

[Joe L.]

Re: C2- PCV?

John-----

1965 Corvettes did NOT use a PCV valve in the PCV system.

[William C.]

Re: C2- PCV?

'65 used a fitting in the side of the carb that contained a calibrated hole to supply a constant vacuum to the crancase via the hose from the carburetor fitting to the fitting in the side of the oil fill tube.

[John H.]

Re: C2- PCV?

That elbow is a "special" fitting, with an .090" orifice in it to "meter" the flow of crankcase vapors into the air horn; the orifice should be cleaned out with a piece of stiff wire regularly, as it tends to get "carboned-up" and clogged, at which point the system stops working. The "metered orifice" fitting arrangement was replaced by the fill tube-mounted PCV valve for the 1966 model year.

[Duke W.]

Re: C2- PCV?

Under manifold vacuum conditions with this system, fresh, filtered air is drawn past the wire mesh flame arrestor on the air cleaner base and through the large tube to the crankcase opening behind the distributor, circulated through the crankcase, and the fresh air and blowby are drawn via the calibrated
orifice in the carburetor fitting, connected to a carburetor vacuum port via the hose leading from the oil fill pipe.

Under WOT conditions where there is little manifold vacuum, crankcase pressure is relieved by the blowby gas venting to the inside of the air cleaner and drawn into the engine for combustion. This means that this particular system design can flow both ways.PCV systems that have a metering/anti-backfire valve usually only flow one way.

Since yor system does not have a valve with an antibackfire feature, that little hemispherical screen on the base of the air cleaner is very important. It is a flame arrestor, and without it, an inlet backfire could propagate to the crankcase and cause an explosion. The blowby gas is mostly unburned fuel air mixture with some exhaust products, and it is COMBUSTIBLE!

Duke

[john Pickens]

Re: C2- PCV?

So how does obstruction of flow, such as with carbon deposition, affect overall
performance and how much of a factor is this in reality?

[Duke W.]

Re: C2- PCV?

If the metering orifice in the carb fitting becomes blocked it will prevent
proper functioning of the PCV system during engine operation other than
WOT. Keeping the orifice clean is simply a matter of periodically taking
the fitting off the carb and soaking it in carb cleaner. Likely this has never or rarely been done on some engines, so it would be a good idea to go ahead and perform this service. For engines with a valve, the valve should be periodically checked for proper function (see the requisite servcie manual), and it too can be soaked in carb cleaner as all the OEM valves are all metal. If you clean the PCV valve regularly, you can just use mineral spirits, as the valve will likely only have an oil film in it, not hard deposits.

BTW, all the hardware for the PCV system should be shown in the base engine section of the AIM, and any differences for RPO engines will be shown in the appropriate RPO section.

Duke