Breathe DeeplyQ I own a '33 Chevy five-window coupe; it's chopped, channeled, without fenders, and lots of fun. My problem is a friend of mine had a set of the old seven-fin Corvette valve covers that he didn't want so I bought them. I had them polished and they look great, not a blemish. I want to put them on the small-block 350 in the coupe, but the valve covers are so nice I don't want to drill them for an oil fill or breather. The engine has an Offy tunnel-ram manifold. It does have a hole in the front for a fill tube, so putting in oil is no problem, but what about a PCV valve? Doesn't the engine need a breather, too? A friend of mine told me it was possible to put a PCV valve in the oil fill tube and then back to the carburetor. Wouldn't this pull air through the breather on the tube or does it vent pressure from the pan? I am stuck and really need an answer. Thanks. John BadaVia the Internet
A You're right-positive crankcase ventilation systems draw air from the crankcase, so they must have a means of replacing the air that is removed. Most contemporary V-8s will have the PCV valve in one rocker cover and a tube running from the air cleaner to the opposite rocker cover. Contaminants are drawn through the PCV valve into the intake manifold and ultimately into the cylinders to be burned, while "fresh" air is supplied to the crankcase via the tube from the air cleaner.
As your friend says, it is possible to connect a hose from the oil filler tube to the carburetor and use either an inline PCV valve or one that screws directly into the carburetor (mid-'60s Chevrolets used this arrangement). However, if that is what you use, the filler cap must be the positive seal type and not be vented. Otherwise the engine will pull air from outside, rather than inside the engine.
With the PCV valve dilemma solved, you still have to come up with a way of providing replacement air. One method is to use small breathers on the valve covers. With a PCV system they will become air inlets instead of conventional breathers, so if you do elect to install breathers in this manner, it's a good idea to remove the coarse foam that comes with them and substitute a more effective filtering media as air is coming into the engine through them. A good alternative is the foam used in lawn mower air filters, available at most hardware stores. Just cut it to shape, oil it, and stuff it in the breathers.
Now, if you just flat refuse to cut those Vette valve covers (and I can understand your not wanting to), there is one more option, but it will only work if an electric fuel pump feeds the engine. Make a block-off for the fuel pump out of flat plate. Cut a hole in the center and weld in a tube that is the right diameter to accept a breather and has a 90-degee bend so it comes out from the engine and turns up. The PCV system will pull air through the breather, and with the tube pointing up, any oil that finds its way into it will drain back to the pan.
Rough RodQ Help, I've got a weird problem. My '40 Oldsmobile is powered by a 500ci Cad. The engine is a bone-stock rebuild, and since the day we first fired it, the idle has been rough. The engine has the original Quadrajet carburetor, and the weird part is that the idle mixture screws don't seem to have any effect on the idle quality. My other street rod is a '40 Chevy with a Chevy small-block, and it also has a Quadrajet. It reacts immediately when the idle mixture screws are turned in or out. What's the difference between the two? Bill NoffingerVia the Internet