Rookie here with my first post. I finally got that C2 I've wanted for a long time, and I've been reading the Forum for several weeks just soaking up some of the info, suggestions, etc., and am impressed by the depth of knowledge out there. My new ride is a 1964 convertible, saddle tan, side pipes, 4-speed and a 350 CI engine from parts unknown. The car was built with the 327 250 or 300 HP as evidenced by the low redline tach. My question has to do with engine venting. When I drive the car at moderate engine speeds, less than 4000 rpm, no problem regarding oil leakage. When I use a little wide open throttle and get up around 4500+ rpm several times I start getting smoke from underneath the car--not the exhaust. When I get home and open the hood there's oil slung across the underside of the hood and on the left (driver's side) valve cover and on down to the header, hence the smoke. It's more than a few drops, and its soot black, although the oil has only a 1,000 miles on it.

I talked with a pretty competent mechanic who says the sealed oil fill tube, (see pic of engine) combined with no vents on the valve covers is the problem---there is a vent line with check valve between the oil fill tube and the lower body of the AFB carburetor. I've checked it and line is not plugged and the check valves allows flow from the oil tube toward the carb, but not in the opposite direction. The advice I got was to get rid of the cast aluminum valve covers and put on later vintage steel covers with one vent going to the air cleaner to allow the block to draw in fresh air through the air cleaner, and the other vent to the lower side of the carb to allow the engine vacuum at low speed to suck in the air and entrained oil. What he says makes sense, but the set up I have worked for years prior to 1968--so why won't mine?

Oh, additional info on the engine that I've pieced together if it helps: 350 Cu.In., 1978 block designed for 195 HP service. Heads are, casting number 3890462, intake is 3844461, carb is 625 cfm Carter AFB and cam is some sort of high lift with machined rocker arms requiring 3/8" high lift-spacers under the valve covers to provide adequate clearance for the rockers, idle is very rough and engine doesn't smooth out till 2,200 rpm. Compression measured at +/-175 psi in each cylinder.

Any advice or insight you have would be a big help. My plan is to tackle this problem, and if I can get it figured out, then think about a more cruising friendly cam. I've read the threads and will approach that topic carefully, folks seem pretty passionate about cam selection (humor).

 

My son is experiencing this same issue on his 1970 454 Chevelle. One suggestion was blow by due to the lack of baffles on the valve covers.

 

Congratulations on your beautiful 64 corvette.

I believe your mechanic gave you very good advice, get a pair of later aluminum valve covers with the factory baffles and PCV on one side and breather to air cleaner on the other side, that's the best set up because of the location of the breather/PCV holes on the top of the rocker box.

You have what looks like a very nice pair of 63-65 valve covers without the flaw through the O in the word Corvette, you may want to hang on to them.

With that camshaft try a PCV from a high hp engine or make one with a .100 hole and plumb it to the rear of the carburetor under the throttle plate like where the vacuum advance is currently, in 64-65 that's how GM did the valve. Run the V/A line to the front and make sure it's connected to the full manifold port, with that cam you need to give the engine idle air without cranking open the primary throttle blades to much because you will over expose the transfer slot and make it rich.

That cam has to be work to drive on the street unless the car has a low rear gear.

 

The 350 engine doesn’t have the rear vent tube like the 327 Block. From what I see, you don’t have a fresh air intake. You can do what I did on my 350, machine drill a hole at the rear of the intake, add a baffle and a PCV and run it to the carb. The fill tube at the front of the intake with breather cap provides fresh air intake and you don’t have to punch holes in your valve covers. Works great.

 

easiest, best way out.

 

Excellent feedback, it seems you all agree I need a fresh air intake for the block and an easy way for blow by air to reach the intake--that's what I'll do.

And, tbarb, you are right, the car is absolutely a chore to drive in town and rough on the drive train and the driver. My project will be to choose a milder cam/tappet/rocker~ set up and do this all in one effort. I would think there's a ~300 HP cam for a 350 CI from GM, I just got to figure out which one and make the change.

Thanks for the info folks, much appreciated.

 

Did your mechanic suggested a vented breather and catch can as well?

 

I think you need to find out where all that oil is blowing out of the engine. Your crankcase is effectively sealed to the outside the way it is plumbed so how/where is the oil getting out? Do you have a valve cover gasket blown out for example?

 

I would decide what you want for an engine combo when you are all said and done, before you start.

If it were my car; I would stay with a Mechanical cam shaft. The LT-1 would be great in your 350. Go back to stock valve train. Acquire a Holley 2818-1 or similar carb, which is suppose to be on that intake manifold. The carb you have is not suited for the cam you have unless it has been modified.

 

Find and fix the leak, first, and add a crankcase pressure relief.

Valve cover gaskets, and spacer gaskets, are weak gasket sealing areas. Check the cover gaskets and take care setting and sealing new gaskets.

A 55-62 style vented oil fill tube cap will make a temporary fix to relieve the excessive crankcase pressure to prevent future gasket blow outs (temporary, because it should be changed to a remote crankcase air inlet). This temporary fix relieves pressure, and gasket blow outs, but will not draw air through the engine to remove contaminated air with combustion blow by and acids from the crankcase that promote sludge in the engine.

You need a crankcase air inlet located apart from the PCV fitting: in the drivers side valve cover, or into taller drivers side valve cover spacer (what I have done), or manifold, or the block's rear china wall, or oil pan. A fresh air intake separated from the PVC porting that penetrates into the engine crankcase or lifter valley is preferred to draw air through the crankcase. The remote vent will carry fresh air in, and flow air through the engine to the PCV valve, to assure the contaminated blow by air in the crankcase is purged with flow-through ventilation.

The goal is fresh air in at a remote location, and out at the oil fill tube PVC setup that you have.

Don't get too set on major changes too soon. Having the timing and advance curve in the distributor (with a properly working vacuum advance) improves the character of a lumpy cam at idle. I would also check and set valve lash to the cam specs (30-30, or whatever), and if it is still too lumpy experiment with slightly looser lash to tame the idle

Those are nice original valve covers (keepers), on a very good looking 64'. You have a very nice car to enjoy. Welcome to the forum.

 

If that engine doesn't smooth out until 2,200 rpm, I suspect a big vacuum leak. With that much cranking compression, it doesn't sound like that cam is all that wild. But I'll let one of the experts speak to that if they like.

Unhook the hose from your "check valve" to the carb and block the port in the caraburetor and see if your engine smooths out any.

 

new block with old venting. The 350 vented valve cover to valve cover. The car WILL run rough because the crank case pressure that is pushing oil past the seals is also pushing oil past the bottom oil control ring on every piston which will foul your plugs.

Dom

 

But I would think it would make the exhaust smoke and he says there is no exhaust smoke.

But he could have fouled plugs anyway to make it run rough.

 

Good point! Maybe the exhaust smoke is minor and mixing with under car smoke?

Dom

 

This is good advice. Plug the carb vacuum ports off, leave the oil fill cap off, check the spark plugs, then run the engine at idle.

Hook up a vacuum gauge and let us know what the vacuum is at varias idle speeds.

As mentioned, that carb is not designed to supply the amount of idle bleed air for the cam you have. Simply turning the curb idle screw up to set a higher idle is negating your entire idle mixture circuit.

 

What is your engine's manifold vacuum @ idle speed RPM?

At what speed are you measuring the idle vacuum?

 

Without knowing the cam specs beforehand, it's not helpful to speculate about vacuum leaks.

 

This question comes up often and there are always members with good intentions to help but often they further confuse the OP because they are citing what THEY have on their cars. The systems for getting rid of the crankcase pressure/vapors progressed and changed over the years. The information below shows this progression so you can determine how your car originally came from the factory. Some of the later systems are much better for the health of your engine and you MAY be able to adapter your C1 or C2 car to one of these systems provided you have an early block with the original draft tube hole located at the back near the distributor. If you have a later replacement block that does not have this hole there are ways to adapt these engines and still run your original type finned aluminum valve covers. First you need to decide if it is important to you to keep as much of an original looking engine compartment or not. If you don’t care about this then the simplest way to do it is by replacing your valve covers with later year covers that have the holes for the PVC valve or breathers. In addition to the below CRANKCASE VENTILATION AND PCV 101 information I am also providing some methods of converting your car and being able to keep your original valve covers or replacing them with something stealthy that is not immediately noticeable.


CRANKCASE VENTILATION AND PCV 101



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 200-degree hurricane, with hot oil flying everywhere, along with steam, raw fuel, and constant high-pressure pulses of blow-by contaminants and combustion by-products. If all that ugly acidic stuff stays there and just keeps circulating, it eventually breaks down the oil’s detergent additives and begins to form sludge.



How does the engine design deal with this, how does it work, what does it look like, and what kind of maintenance does it require? What we’re talking about here is the PCV (Positive Crankcase Ventilation) system; let’s de-mystify it and follow its development from the ’53 Corvette up through the 80’s.



Crankcase Ventilation: There’s no way around the necessity to ventilate the inside of the engine; pressure builds up in there, and it has to be relieved, and the hot (and flammable) gases have to be exhausted and replaced with fresh air to continue the ventilation process. Three things are required for crankcase ventilation; air intake, an oil/vapor separator to let vapors out and keep oil in, and an exhaust point that will continuously pull out the vapors.



Crankcase Ventilation In The 50’s: For decades, up through the 50’s, engine designers simply provided a way to get outside air into the engine and vent crankcase vapors out, without losing oil along with the vapors. Emissions weren’t a concern (yet) in those days, so the hot vapors were simply drawn out into the atmosphere; we’ll refer to these as “open” crankcase ventilation systems.



The “Blue Streak” six-cylinder Corvette engine used open slots in the top of the valve cover as an entry point for outside air, and an external oil/vapor separator canister mounted in a hole in the side of the crankcase which exhausted through a “road draft tube” mounted next to the oil pan. The bottom end of the road draft tube was shaped and cut at an angle so it tended to create a low-pressure area when the car was moving at road speed, which helped pull hot crankcase vapors out of the engine and through the separator can and tended to pull some outside air into the crankcase through the slots in the valve cover. When the car wasn’t moving or was in slow traffic, internal pressure just blew hot oil vapors out of both places, resulting in a dirty, oily mist coating on top of the engine.



The V-8’s from ’55 through ’62 used essentially the same principle, except the entry point for outside air was through the vented oil fill cap, which was packed with steel mesh to filter incoming air and to reduce oil misting on top of the engine. The V-8’s used an oil/vapor separator canister mounted inside the lifter valley which fed the outlet in the back of the block where the road draft tube was attached, adjacent to the distributor.



Both of these systems provided pressure relief, but were only marginally effective in ventilating the crankcase, and dumped all the hydrocarbon-laden hot oil vapors directly into the atmosphere. Solid-lifter engines that were run hard at continuous high-rpm (racers) blew a lot of oil mist out of the vented filler cap all over the top of the engine, and Engineering responded to those complaints by releasing non-vented fill caps on those engines. That solved the racer’s oil misting complaints, but also rendered the primitive crankcase ventilation system nearly useless; with a sealed oil fill cap, all the road draft tube really provided was pressure relief, but in those days, nobody cared.



Progress In The 60’s: Aside from an early attempt at a primitive “closed” system (RPO 242) in 1961-62 for California cars, all Corvettes through 1962 had “open” (to the atmosphere) crankcase ventilation systems. 1963 brought a new Corvette, and a new “closed positive” crankcase ventilation system design philosophy as well.



The 1963 “closed” ventilation system, used on all engines, used the oil fill tube as the “intake” side of the system, to admit outside air into the crankcase, and used a hose from the hole in the back of the block (previously used for the road draft tube) to the base of the carburetor as the “exhaust” side of the system.



At the “intake” side, a hose carried outside air from a fitting on the “clean” side of the bottom front of the air cleaner to a fitting on the oil fill tube. At the “exhaust” side, the hose from the vent hole in the back of the block had a PCV valve where it connected to the carburetor base. The valve was exposed to full manifold vacuum, which “pulled” outside air through the crankcase, carrying the hot vapors into the intake manifold to be burned along with the intake charge. The PCV valve is essentially a spring-loaded one-way check valve, which only allows flow through it in one direction under certain vacuum conditions.



The “closed positive” ventilation system used engine vacuum to force a continuous flow of fresh air through the crankcase, and burned the vapors as part of the normal combustion process instead of exhausting them directly into the atmosphere. This finally created a controlled ventilation system to reduce sludge formation, and reduced hydrocarbon emissions into the atmosphere.



Changes For 1964: Continuing development indicated that the system’s efficiency was improved by reversing the ventilation airflow so the “intake” side was through the vent hole in the back of the block, and the “exhaust” side was through the oil filler tube to the carburetor.



The “intake” side used a steel adapter and large-diameter vent pipe at the vent hole in the back of the block, connected by a large rubber hose to an elbow in the bottom of the air cleaner, so clean air was drawn from the air cleaner into the back of the block. Inside the air cleaner, a steel fine mesh screen was pressed over the stub on the elbow as a “flame arrestor”; this prevented a carburetor backfire from propagating through the vent tube into the crankcase, which could cause an explosion. The same
type of flame arrestor technology is used for the air cleaner element on inboard marine engines so a carburetor backfire won’t ignite bilge fumes.



The “exhaust side” of the system was moved to the oil fill tube, which had a fitting for a hose to a manifold vacuum source at the carburetor; engines with Carter WCFB or AFB carburetors continued to use a PCV valve and fitting at the back of the baseplate. The 365hp engine used a Holley carburetor, with a slightly different arrangement; the hose from the oil fill tube connected to a 90° fitting on the driver’s side of the carburetor with an internal .090” restrictor orifice instead of a PCV valve. The orifice in the fitting was supposed to be cleaned with a fine wire at each tune-up interval; if the orifice became plugged, the crankcase ventilation system ceased to operate, and crankcase vapors would be driven up the rear vent tube into the air cleaner. The 1964 system design continued unchanged into 1965 for small-block engines.



Fuel-injected engines used the same basic design (“intake” from the air cleaner, and “exhaust” from the oil fill tube to the intake plenum), although the plumbing was different.



1965 Big-Block: When the 396 was introduced in mid-1965, a new PCV system design came with it; there was no vent hole in the back of the block, and there was no oil fill tube in the intake manifold. The air cleaner still provided the “intake” side of the system, but it was connected to an elbow in the passenger side valve cover; the “exhaust” side used a pipe from the driver’s side valve cover to a restrictor fitting on the driver’s side of the Holley carburetor.



Why was the “exhaust” side in the driver’s side valve cover instead of on the passenger side? With the crank and rods rotating clockwise as viewed from the front, oil was thrown “up” toward the bottom of the oil drainback holes on the passenger side, and was thrown “down”, away from the bottom of the oil drainback holes on the driver’s side. Had the “exhaust” side of the system been placed in the passenger side valve cover, it would have tended to pick
type of flame arrestor technology is used for the air cleaner element on inboard marine engines so a carburetor backfire won’t ignite bilge fumes.



The “exhaust side” of the system was moved to the oil fill tube, which had a fitting for a hose to a manifold vacuum source at the carburetor; engines with Carter WCFB or AFB carburetors continued to use a PCV valve and fitting at the back of the baseplate. The 365hp engine used a Holley carburetor, with a slightly different arrangement; the hose from the oil fill tube connected to a 90° fitting on the driver’s side of the carburetor with an internal .090” restrictor orifice instead of a PCV valve. The orifice in the fitting was supposed to be cleaned with a fine wire at each tune-up interval; if the orifice became plugged, the crankcase ventilation system ceased to operate, and crankcase vapors would be driven up the rear vent tube into the air cleaner. The 1964 system design continued unchanged into 1965 for small-block engines.



Fuel-injected engines used the same basic design (“intake” from the air cleaner, and “exhaust” from the oil fill tube to the intake plenum), although the plumbing was different.



1965 Big-Block: When the 396 was introduced in mid-1965, a new PCV system design came with it; there was no vent hole in the back of the block, and there was no oil fill tube in the intake manifold. The air cleaner still provided the “intake” side of the system, but it was connected to an elbow in the passenger side valve cover; the “exhaust” side used a pipe from the driver’s side valve cover to a restrictor fitting on the driver’s side of the Holley carburetor.



Why was the “exhaust” side in the driver’s side valve cover instead of on the passenger side? With the crank and rods rotating clockwise as viewed from the front, oil was thrown “up” toward the bottom of the oil drainback holes on the passenger side, and was thrown “down”, away from the bottom of the oil drainback holes on the driver’s side. Had the “exhaust” side of the system been placed in the passenger side valve cover, it would have tended to pick
type of flame arrestor technology is used for the air cleaner element on inboard marine engines so a carburetor backfire won’t ignite bilge fumes.



The “exhaust side” of the system was moved to the oil fill tube, which had a fitting for a hose to a manifold vacuum source at the carburetor; engines with Carter WCFB or AFB carburetors continued to use a PCV valve and fitting at the back of the baseplate. The 365hp engine used a Holley carburetor, with a slightly different arrangement; the hose from the oil fill tube connected to a 90° fitting on the driver’s side of the carburetor with an internal .090” restrictor orifice instead of a PCV valve. The orifice in the fitting was supposed to be cleaned with a fine wire at each tune-up interval; if the orifice became plugged, the crankcase ventilation system ceased to operate, and crankcase vapors would be driven up the rear vent tube into the air cleaner. The 1964 system design continued unchanged into 1965 for small-block engines.



Fuel-injected engines used the same basic design (“intake” from the air cleaner, and “exhaust” from the oil fill tube to the intake plenum), although the plumbing was different.



1965 Big-Block: When the 396 was introduced in mid-1965, a new PCV system design came with it; there was no vent hole in the back of the block, and there was no oil fill tube in the intake manifold. The air cleaner still provided the “intake” side of the system, but it was connected to an elbow in the passenger side valve cover; the “exhaust” side used a pipe from the driver’s side valve cover to a restrictor fitting on the driver’s side of the Holley carburetor.



Why was the “exhaust” side in the driver’s side valve cover instead of on the passenger side? With the crank and rods rotating clockwise as viewed from the front, oil was thrown “up” toward the bottom of the oil drainback holes on the passenger side, and was thrown “down”, away from the bottom of the oil drainback holes on the driver’s side. Had the “exhaust” side of the system been placed in the passenger side valve cover, it would have tended to pick
up more liquid oil from that side, which would cause high oil consumption and smoking in the exhaust.



The 1965 big-block PCV system design would evolve several years later into the system used on all Corvette V-8 engines.



1966 Changes: The “intake” side of the PCV system didn’t change for 1966; however, the restrictor fittings used on the “exhaust” side with Holley carburetors proved troublesome in the field (clogging the .090” orifice, resulting in oil in the air cleaners), so all 1966 engines got PCV valves instead of restrictor fittings (all 1966 engines had Holley carburetors).



Small-blocks got a revised oil fill tube with a threaded bung which accepted a screw-in PCV valve, with a hose from the other end of the valve to a large nipple on the passenger side of the Holley baseplate. The big-block engines used a PCV valve in the driver’s side valve cover (instead of the pipe used in 1965), with a hose to the passenger side of the Holley baseplate.



The PCV valve did a far more effective job of metering the flow of crankcase vapors under a wide range of operating conditions than the previously-used restrictor fittings, and were far less susceptible to clogging due to the constant movement of the spring-loaded internal pintle. Maintenance was also simple – remove the valve and shake it; if it rattled, it was OK. The 1966 PCV systems carried over into 1967 without change.



What About The L-88?: The 1967 L-88 made no pretense about having a PCV system, as it was intended purely as a race car, with no emission system of any kind, and had a race car’s crankcase ventilation system; a vented breather cap on the passenger side valve cover as the “intake” point, and an external oil/vapor separator canister and long road draft tube plugged into the driver’s side valve cover – the same type of primitive “open” system used on 1953-1962 Corvettes.



1968, however, brought new emission requirements, and the L-88’s crankcase ventilation system grew up; it used the same closed positive system used on other Corvettes, with an “intake” from the air cleaner and a flame arrestor screen, and a PCV valve and hose to the carburetor from the driver’s side valve cover. It also used the same A.I.R. emission system as other Corvettes.



1968 Changes: 1968 brought the elimination of the oil fill tube in the intake manifold and the vent hole in the back of the block on small-blocks, so they adopted the same PCV system design introduced on the big-block in 1965; “intake” from the air cleaner into the passenger side valve cover, and “exhaust” through a PCV valve in the driver’s side valve cover with a hose to the carburetor baseplate. The oil/vapor separator canister in the lifter valley was also eliminated, and was replaced by baffles inside the valve cover at the PCV valve location to minimize pickup of liquid oil. This same basic PCV system design concept has remained in production ever since.



Maintenance: PCV system maintenance is pretty simple; if you have a fixed orifice fitting, remove it and clean it with a fine wire to make sure it remains open. If you have a PCV valve, shake it and make sure it rattles; if it doesn’t, clean it with solvent or carb cleaner until it does rattle, or replace it. Check the fine-screen flame arrestor in the air cleaner and clean it if necessary; if it’s clogged, the PCV system won’t work.



Misconceptions And Modifications: Conventional wisdom is that PCV systems somehow reduce performance as a result of introducing crankcase vapors into the intake charge and diluting it; this is a bad assumption, as the amount of vapors metered by the PCV valve is pretty insignificant compared to the weight of the primary air/fuel charge. It would take NASA-level instrumentation to show any difference in power output.



Modified engines with no provisions for the PCV system and situations where early “no-hole” valve covers are used
on late blocks with no rear vent hole and no oil filler tube in a late intake manifold create a number of problems. Generally, these situations end up with one or more “breathers” somewhere, which provide little more than pressure relief, no ventilation, and result in hot oil misting in the engine compartment.



There ARE solutions for modified engines – it just takes a little ingenuity to provide an “intake” point and an “exhaust” point with a PCV valve and hose to the carburetor, even if you need to drill one or both of the valve covers to provide them. PCV ventilates your crankcase, keeps your oil clean longer, reduces the likelihood of sludge formation, and burns all those noxious fumes and hydrocarbons that would otherwise be dumped into the atmosphere; it’s good for your engine, and for the environment as well.



There’s no mystery about the PCV system; it’s like having a window open at both ends of your house when a stiff breeze is blowing. Fresh air comes in one end and carries stale air out the other end; as long as both windows remain open, the system works. Keep the windows open!


Link to: How to modify your existing valve covers for pcv that is not very noticable. Look at the below link and starting at post 14 there are some good examples. Make sure the the baffle inside the valve cover for the hole for the PCV valve is enclosed on the side and bottom so the pressure is being relieved through the opening in the baffle at the TOP so it does not get flooded with oil during hard acceleration. With this adaptation to your valve cover you can create either an closed system or a highbred open/closed system depending on weather you have a vented oil breather cap or a closed (tight fitting) cap. You can run the system in either direction, see the CRANKCASE VENTILATION AND PCV 101 in the section about the system being reversed in 1964. I would caution you that this system used an internal .090” restrictor orifice instead of a PCV valve on the 365 h.p. engines and it needs to be cleaned often or it will clog and not allow the crankcase to breathe.
https://www.corvetteforum.com/forums...e-and-pcv.html


Link to: New factory made modified valve covers for vintage look with stealthy vent holes—expensive
https://www.yourcovers.com/valve_cov...1026_holes.pdf

 

Thanks to all, great info:

Mike M - You're right, venting is part of the problem which I'll attack, but I need to find where the oil is coming from too. I suspect it's my valve covers with spacers and two cork gaskets each..

63-340 I do plan to work on the carb/cam set up next, after I get the venting thing handled. I didn't realize the AFB was a bad mate to the 461 intake and 462 heads.

Ghost Rider Vacuum gauge and measurements on the engine are first step--thanks

68Hemi Amazing level of detail-- reading this twice I think I've finally got a grasp on the concept. My engine builder got half the job done; I need to add that fresh air intake and will.

I'll up-date you guys once I've tried to add the vent and look at vacuum levels. Thanks again.

Phil

 

Thanks to all, great info:

Mike M - You're right, venting is part of the problem which I'll attack, but I need to find where the oil is coming from too. I suspect it's my valve covers with spacers and two cork gaskets each..

63-340 I do plan to work on the carb/cam set up next, after I get the venting thing handled. I didn't realize the AFB was a bad mate to the 461 intake and 462 heads.

Ghost Rider Vacuum gauge and measurements on the engine are first step--thanks

68Hemi Amazing level of detail-- reading this twice I think I've finally got a grasp on the concept. My engine builder got half the job done; I need to add that fresh air intake and will.

I'll up-date you guys once I've tried to add the vent and look at vacuum levels. Thanks again.

Phil