Crankcase Ventilation And PCV1 icTl MAKING YOUR CORVETTE'S ENGINE BREATHE TAKES MORE THAN A CLEAN BY JOHN HINCKLEY

Within your engine, under the valve covers and inside that crankcase and lifter valley is a pretty ugly environment. It's like a ZOO degree hurricane, with hot oil flying everywhere, along with steam, raw fuel, and constant high-pres• sure pulses of blow-by contaminants and combustion byproducts. If all that ugly acidic stuff stays there separator to let vapors out and keep area when the was moving at road and just keeps circulating, it eventually oil in, and an exhaust point that will speed, which helped pull hot crankcase breaks down the oil's detergent additives continuously pull out the vapors. vapors out of the engine and through and begins to form sludge. For decades, up through the '50s, the separator can, pulling some outside How does the engine's design deal engine designers simply provided a way air into the crankcase through the slots with this, how does it work, what does it to get outside air into the engine and vent in the valve cover. When the car wasn't look like, and what kind of maintenance crankcase vapors out, without losing oil moving or was in slow traffic, internal does it require? What we're talking about along with the vapors. Emissions weren't pressure just blew hot oil vapors out of here is the PCV (Positive Crankcase a concern (yet) in those days, so the both places, resulting in a dirty, oily mist Ventilation) system; let's de-mystify it hot vapors were simply drawn out into coating on top of the engine. and follow its development from the '53 the atmosphere. We'll refer to these as The V-8s from '55 through '62 used Corvette up through the '80s. "open" crankcase ventilation systems. essentially the same principle, except The " BI ue Streak" s ix-cy I i nder Corvette the entry point for outside air was CRANKCASE VENTILATION: There's no engine used open slots in the top of the through the vented oil fill cap, which way around the need to ventilate the valve cover as an entry point for outside was packed with steel mesh to filter inside of the engine. Pressure builds up air, and an external oil/vapor separator incoming air and to reduce oil misting in there and it has to be relieved, and canister mounted in a hole in the side of on top of the engine. The V-8s used an the hot (and flammable) gases have to the crankcase which exhausted through oil/vapor separator canister mounted be exhausted and replaced with fresh a "road draft tube" mounted next to the inside the lifter valley that fed the air to continue the ventilation process. oil pan. The bottom end of the road draft outlet in the back of the block where Three things are required for crankcase tube was shaped and cut at an angle the road draft tube was attached, ventilation: air , an oil/vapor so it tended to create a low-pressure adjacent to the .

60 CORVETTE ENTHUSIAST Both of these systems provided as well. 1 Note the open "slot" in the valve cover next to the pressure relief, but were only marginally The 1963 "closed" ventilation system, oil fill cap on this '54; it's the "intake" point for the effective in ventilating the crankcase, used on all engines, used the oil fill tube crankcase vent system. Normally this area is heavily and dumped all the hydrocarbon- as the "intake" side of the system to oil-misted. laden, hot oil vapors directly into the admit outside air into the crankcase, and atmosphere. Solid-lifter engines that used a hose from the hole in the back of 2 The black object in the center is the oil/vapor separator were run hard at continuous high rpm the block (previously used for the road canister on this '54, with the road draft tube extending (racers) blew a lot of oil mist out of the draft tube) to the base of the as down below the frame. If the car was moving, it drew vented filler cap all over the top of the the "exhaust" side of the system. some fumes out of the crankcase. engine. Engineering responded to those At the "intake" side, a hose carried complaints by releasing non-vented outside air from a fitting on the "clean" 3 The oil fill tube is the "intake" side of the ventilation fill caps on those engines. That solved side of the bottom front of the air system on this '57 - typical of all Corvettes through 1962. the racer's oil misting complaints, but cleaner to a fitting on the oil fill tube. also rendered the primitive crankcase At the "exhaust" side, the hose from 4 The "vented" oil fill cap used on the oil fill tube through ventilation system nearly useless. With a the vent hole in the back of the block 1962. Most solid-lifter engines used a non-vented cap, to sealed oil fill cap, all the road draft tube had a PCV valve where it connected stop heavy oil-misting under race conditions. really provided was pressure relief, but to the carburetor base. The valve was in those days, nobody cared. exposed to full , 5 The black object in the center is the adapter elbow for Aside from an early attempt at a which "pulled" outside air through the the road draft tube, bolted into the vent hole in the back primitive "closed" system (RPO 242) crankcase, carrying the hot vapors into of the block. The tube runs behind the distributor and in 1961-'62 for California , all the intake manifold to be burned along down past the . Corvettes through 1962 had "open" (to with the intake charge. The PCV valve the atmosphere) crankcase ventilation is essentially a spring-loaded one-way 6 Hard to see, but the black pipe between the plug wires systems. 1963 brought a new Corvette, check valve, which allows flow through and the braided ground strap is the bottom end of the and a new "closed positive" crankcase it only in one direction under certain road draft tube, where oil vapors were exhausted into the ventilation system design philosophy vacuum conditions. atmosphere with the "open" systems through 1962.

CORVETTE ENTHUSIAST 61 7 The one-year-only 1963 PCV system used the oil fill the "intake" side was through the vent tune-up interval; if the orifice became tube as the "intake" side of the system. Note the hose hole in the back of the block, and the plugged, the crankcase ventilation from the fill tube to the front of the air cleaner. "exhaust" side was through the oil filler system ceased to operate, and crankcase tube to the carburetor. vapors would be driven up the rear vent 8 This small pipe from the vent hole in the back of the The "intake" side used a steel adapter tube into the air cleaner. The 1964 block on a '63 ran behind the distributor and joined a and large-diameter vent pipe at the system design continued unchanged hose to the carburetor. vent hole in the back of the block, into 1965 for small-block engines. connected by a large rubber hose to an Fuel-injected engines used the same 9 Mere's the other end of the '63 pipe, with the rubber elbow in the bottom of the air cleaner, basic design ("intake" from the air hose to the carburetor. so clean air was drawn from the air cleaner, and "exhaust" from the oil fill cleaner into the back of the block. tube to the intake plenum), although 10 Here's the '63 hose, with a PCV valve, connected to a Inside the air cleaner, a steel fine-mesh the plumbing was different. tee fitting at the back of the AFB carburetor. System flow screen was pressed over the stub on When the 396 was introduced in was reversed for 1964. the elbow as a "flame arrestor." This mid-1965, a new PCV system design prevented a carburetor backfire from came with it. There was no vent hole in 11 The block vent hole adapter and pipe to the air propagating through the vent tube into the back of the block, and there was no cleaner, which became the "intake" side of the system the crankcase, which could cause an oil fill tube in the intake manifold. The from 1964-1967. explosion. The same type of flame- air cleaner still provided the "intake" arrestor technology is used for the air side of the system, but it was connected cleaner element on inboard marine 12 The 1964'65 Holley "exhaust side" arrangement, to an elbow in the passenger side valve engines so a carburetor backfire won't with a hose from the oil fill tube to the elbow restrictor cover. The "exhaust" side used a pipe ignite bilge fumes. fitting on the side of the carburetor. from the driver's side valve cover to a The "exhaust side" of the system was restrictor fitting on the driver's side of The "closed positive" ventilation system moved to the oil fill tube, which had a the Holley carburetor. used engine vacuum to force a continuous fitting for a hose to a manifold vacuum Why was the "exhaust" side in the flow of fresh air through the crankcase, and source at the carburetor. Engines with driver's side valve cover instead of on burned the vapors as part of the normal Carter WCFB or AFB the passenger side? With the and combustion process instead of exhausting continued to use a PCV valve and fitting rods rotating clockwise as viewed from them directly into the atmosphere. This at the back of the baseplate. The 365hp the front, oil was thrown "up" toward finally created a controlled ventilation engine used a Holley carburetor, with the bottom of the oil drainback holes system to reduce sludge formation, and a slightly different arrangement. The on the passenger side, and was thrown reduced hydrocarbon emissions into the hose from the oil fill tube connected "down," away from the bottom of the atmosphere. to a 90° fitting on the driver's side of oil drainback holes on the driver's side. Changes for 1964 were a result of the carburetor with an internal .090" Had the "exhaust" side of the system continuing development that indicated restrictor orifice instead of a PCV valve. been placed in the passenger side valve that the system's efficiency was improved The orifice in the fitting was supposed cover, it would have tended to pick up by reversing the ventilation airflow so to be cleaned with a fine wire at each more liquid oil from that side, which

62 CORVETTE ENTHUSIAST would cause high oil consumption and the other end of the valve to a large 13 Close-up view of the Holley restrictor fitting. It contains smoking in the exhaust. nipple on the passenger side of the a .090" orifice that needs cleaning at every tune-up The 1965 big-block PCV system Holley baseplate. The big-block engines interval, or oil will build up in the air cleaner. design would evolve several years later used a PCV valve in the driver's side into the system used on all Corvette V-8 valve cover (instead of the pipe used in 14 For 1966, a PCV valve was introduced, which threaded engines. 1965), with a hose to the passenger side into a bung on the oil fill tube. It replaced the previous The "intake" side of the PCV system of the Holley baseplate. restrictor fitting in the "exhaust" side of the system. The didn't change for 1966; however, the The PCV valve did a far more valve meters the flow of crankcase vapors based on restrictor fittings used on the "exhaust" effective job of metering the flow engine vacuum. side with Holley carburetors proved of crankcase vapors under a wide troublesome in the field (clogging the range of operating conditions than the 15 An original '67 CV726C PCV valve. The left end .090" orifice, resulting in oil in the air previously used restrictor fittings, and threads into the oil fill tube, the right "exhaust" end cleaners), so all 1966 engines got PCV was far less susceptible to clogging due accepts a hose to the carburetor. valves instead of restrictor fittings (all to the constant movement of the spring- 1966 engines had Holley carburetors). loaded internal pintle. Maintenance Small-blocks got a revised oil fill tube was also simple - remove the valve with a threaded bung, which accepted and shake it; if it rattled, it was OK. a screw-in PCV valve, with a hose from The 1966 PCV systems carried over

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CORVETTE ENTHUSIAST 63 16 The other end of the hose from the PCV valve con• into 1967 without change. same closed positive system used on nects to the carburetor base. This is an AJ.R.-equipped other Corvettes, with an "intake" from car, with the connection at the rear of the carb instead WHAT ABOUT THE L-88? The 1967 L-88 the air cleaner and a flame-arrestor of on the side. made no pretense about having a PCV screen, and a PCV valve and hose to system, as it was intended purely as a race the carburetor from the driver's side 17 The "intake" side of the '67 L-88 "open" system; just a car with no emission system of any kind, valve cover. It also used the same A.I.R. vented breather cap on the passenger-side valve cover. and had a race car's crankcase ventilation emission system as other Corvettes. system - a vented breather cap on the 1968 brought the elimination of the 18 The "exhaust" side of the '67 L-88 system - an external passenger side valve cover as the "intake" oil fill tube in the intake manifold and oil/vapor separator canister and road draft tube, just like point, and an external oil/vapor separator the vent hole in the back of the block the '53'64 six-. The '67 L-88 was a race car with canister and long road draft tube plugged on small-blocks, so they adopted the no emission controls, not a street machine. into the driver's side valve cover - the same PCV system design introduced on same type of primitive "open" system the big-block in 1965: "intake" from used on 1953-1962 Corvettes. the air cleaner into the passenger side 1968, however, brought new emission valve cover, and "exhaust" through a requirements, and the L-88's crankcase PCV valve in the driver's side valve cover ventilation system grew up. It used the with a hose to the carburetor baseplate.

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64 CORVETTE ENTHUSIAST The oil/vapor separator canister in the necessary. If it's clogged, the PCV system 19 The '68 L-88 had both A.I.R. and PCV systems. Note lifter valley was also eliminated, and was won't work. the "intake" hose from the valve cover to the air cleaner replaced by baffles inside the valve cover and the flame arrestor screen where the elbow enters the at the PCV valve location to minimize MISCONCEPTIONS AND MODIFICATIONS: air cleaner base. pickup of liquid oil. This same basic PCV Conventional wisdom is that PCV systems system design concept has remained in somehow reduce performance as a result 20 The "exhaust" side of the '68 L-88 PCV system. production ever since. of introducing crankcase vapors into Note the PCV valve in the valve cover and hose to the the intake charge and diluting it. This carburetor base. MAINTENANCE: PCV system maintenance is a bad assumption, as the amount of is pretty simple. If you have a fixed orifice vapors metered by the PCV valve is pretty 21 In 1968, small-blocks adopted the big-block PCV fitting, remove it and clean it with a fine insignificant compared to the weight of system when the block vent hole and oil fill tube went wire to make sure it remains open. If you the primary air/fuel charge. It would take away. Here's the "intake" side elbow and hose to the have a PCV valve, shake it and make NASA-level instrumentation to show any air sure it rattles; if it doesn't, clean it with difference in power output. solvent or carb cleaner until it does rattle, Modified engines with no provisions or replace it. Check the fine-screen flame for the PCV system and situations where arrestor in the air cleaner and clean it if early "no-hole" valve covers are used

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CORVETTE ENTHUSIAST 65 mm

r 4 on late blocks with no rear vent hole ventilates your crankcase, keeps your 22 With no oil fill tube, the PCV valve moved to the and no oil filler tube in a late intake oil clean longer, reduces the likelihood driver's side valve cover. This system has remained in manifold create a number of problems. of sludge formation, and burns all those production ever since. Generally, these situations end up with noxious fumes and hydrocarbons that one or more "breathers" somewhere, would otherwise be dumped into the 23 The hose from the valve-cover-mounted PCV valve which provide little more than pressure atmosphere. It's good for your engine, connects to a fitting on the base of the Q-Jet carburetor. relief, no ventilation, and result in hot oil and for the environment as well. This closed positive system is clean, simple, and highly misting in the engine compartment. There's no mystery about the PCV effective. There ARE solutions for modified system; it's like having a window open engines - it just takes a little ingenuity at both ends of your house when a stiff 24 Here's a late 350 block (no rear vent hole) with early to provide an "intake" point and an breeze is blowing. Fresh air comes in valve covers. The owner has adapted an "intake" hose to "exhaust" point with a PCV valve one end and carries stale air out the the air cleaner from the inboard side of the valve cover. and hose to the carburetor, even if other end; as long as both windows Unobtrusive and effective. Just breathers won't get the you need to drill one or both of the remain open, the system works. Keep job done. valve covers to provide them. PCV the windows open! •

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