'66 Malibu N/SA

Woodfin · 08-21-2016, 10:45 AM

a note of trivia about PCV & road draft tubes.

Through the 1962 models Chevrolet had a "road draft tube" for crankcase ventilation. It was a long tube about 1" in diameter connected at the opening you see at the rear of the block, it routed downward slightly below the bottom of the oil pan. It was cut at an angle and in theory "road draft air pull air through the crankcase" Again, in theory, air entered through the front breather and exited the draft tube.

Under some ideal condition with a well sealed engine it may have done so. Mostly, smoke and oil exited both breather and tube

And as miles and sludge accumulated that breather/baffle in your photo would become plugged with sludge. Then the only crankcase vent was the front push on breather.

Beginning with the 1963 models the famous/infamous PVC emerged. At the rear block opening formally attaching the draft tube, Chevy installed a small adapter with a 3/8" hose nipple. The PVC valve was in-line of a length of of 3/8" fuel hose that terminated at a fitting in rear of the carb.

Thus, "positive crankcase ventilation" PCV

About this same timeline all other manufactures changed from draft tubes to PCV

Another piece of trivia, California was ahead of the curve. Some years before 1963 that state began retrofitting PCV systems to older cars.

If you happen to remember the old Popular Hot Rodding magazine Project X It was a 1957 Chevy, in some of the original photos of the car before the magazine began any work there is a photo of the un-touched, original engine. The photo shows a California retrofitted PVC system.

That concludes today's trivia lecture

08-21-2016, 10:45 AM	#30
Woodfin Senior Member Join Date: Sep 2006 Location: Kilgore TX Posts: 540 Likes: 8 Liked 288 Times in 109 Posts	Re: '66 Malibu N/SA a note of trivia about PCV & road draft tubes. Through the 1962 models Chevrolet had a "road draft tube" for crankcase ventilation. It was a long tube about 1" in diameter connected at the opening you see at the rear of the block, it routed downward slightly below the bottom of the oil pan. It was cut at an angle and in theory "road draft air pull air through the crankcase" Again, in theory, air entered through the front breather and exited the draft tube. Under some ideal condition with a well sealed engine it may have done so. Mostly, smoke and oil exited both breather and tube And as miles and sludge accumulated that breather/baffle in your photo would become plugged with sludge. Then the only crankcase vent was the front push on breather. Beginning with the 1963 models the famous/infamous PVC emerged. At the rear block opening formally attaching the draft tube, Chevy installed a small adapter with a 3/8" hose nipple. The PVC valve was in-line of a length of of 3/8" fuel hose that terminated at a fitting in rear of the carb. Thus, "positive crankcase ventilation" PCV About this same timeline all other manufactures changed from draft tubes to PCV Another piece of trivia, California was ahead of the curve. Some years before 1963 that state began retrofitting PCV systems to older cars. If you happen to remember the old Popular Hot Rodding magazine Project X It was a 1957 Chevy, in some of the original photos of the car before the magazine began any work there is a photo of the un-touched, original engine. The photo shows a California retrofitted PVC system. That concludes today's trivia lecture

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