Classic/Antique Car Repair: 1955 Cadillac PCV Valve Add-on, Adding PCV system to older cars

Question
I have a stock 1955 Cadillac Coupe Deville with an all original 331 c.i. and a draft tube.  I would like to add a PCV Valve to update this older motor.  Would a carb re-jetting be necessary?  What is the easiest way of making this update?  Thanks

Answer
There is no need to make any modification to the carburetor - the addition of the small amount of air to the fuel/air mixture via the PCV system is so small as to have almost no effect - and at the very most, all you would have to do is fine-tune the idle mixture screws to improve your idle - but even that is unlikely to be needed.

To make this conversion, you have to seal all openings to the crankcase.  This includes the road draft tube, the oil fill cap and any other opening that would allow air into the inside of the engine.  Then you need to install a PCV valve in an air conduit which leads from the air cleaner to the crankcase.  Usually this is done by making a hole in the air cleaner housing, putting a hose from it to another new hole in one of the valve covers, and installing a PCV valve in the fitting in the valve cover.  This will allow the slight vacuum that exists inside the air cleaner when the engine is running to suck fumes out of the crankcase via the valve cover fitting, thus adding the fumes to the fuel/air mixture entering the carburetor.  This is beneficial to the engine and the environment both, since it removes moisture and corrosive products of combustion leaking past the piston rings from the crankcase, which reduces the acid content of the atmosphere inside the engine quite a bit.  It also has the side benefit of lessening and even eliminating the "old car" smell from the engine.

If you do not want to make a hole in the air cleaner, you can do this another way, that is by installing another fitting on the intake manifold such that the fumes are drawn in directly to the intake manifold, bypassing the air cleaner.  The only downside to this is that the fumes will not then be filtered by the air cleaner system.  If you do it this way, you probably will have to make a minor adjustment to the fuel/air ratio with the idle mixture screws - increasing the fuel slightly, and then reducing the idle speed setting to get your idle speed back down to spec.

Dick