[66sprint6]

Our '67 LeMans came with a '74 400 engine installed in it. It's got the PCV valve in the front of the valley pan with the hose running from it, to the carb base. Shouldn't there be an air intake point for the PCV system somewhere? The motor runs great, but it sure is a hodge-podge of parts. I don't know enough to determine if this is an open or closed system. But I know that it can blow your dipstick out of the tube if it's not working properly.

[Formula8]

Yes, that plug in your passenger side valve cover can be replaced with either a breather or a tube running to your air cleaner and a filter installed in the air cleaner as the factory did.

[lust4speed]

PCV valve purpose is to only remove oil vapor for emission purposes and is not designed to vent built up pressures. With both valve covers blocked your engine is effectively plugged.

[400 Lemans]

Yeah definitely needs to be vented. Also it looks like your thermostat housing is turned around backwards.

[Tom Vaught]

Originally Posted by lust4speed

PCV valve purpose is to only remove oil vapor for emission purposes and is not designed to vent built up pressures. With both valve covers blocked your engine is effectively plugged.

That is not exactly true.

Rarely do you have a completely sealed Piston Ring Package installed on a race engine and never on a production engine.

This means that combustion gases, (from the Power Strokes of the engine) leak past the rings and enter the oil pan. The combustion gases are very corrosive.

Henry ford figured out (with his engineers doing all of the work) that his engines did not last very long in service due to these corrosive gases.
That is when they came up with a "Road Draft Tube system to remove the corrosive gases in the oil pan and valve cover(s) as the engine was going down the road.

The systems worked well except they put these corrosive gases into the earth's atmosphere. Not a big deal in the early days of the Motor cars but a bad deal in the cities as far as pollution of the air in cities of large size like
Las Angeles, Chicago, Detroit, and New York. In a farm community in South Dakota you probably would never have a issue in your lifetime.
BUT THE CORROSIVE GASES NEED TO BE REMOVED FROM THE ENGINE CRANKCASE SYSTEM OR THE DURABILITY OF THE ENGINE PARTS IS REDUCED.

In the farm community you could get away with a road draft system like the 1950s cars had. Still can see the crankcase breather/oil fill tube at the front of the engine on a 55 Chevy engine. The road draft tube is hidden at the back of the engine.

Yes it does remove oil vapor, but the oil vapor has corrosive gases mixes with it in the crankcase and that is what needs to be removed to achieve high mileage engine durability. Henry's old engines, I was told, might last 15,000 miles in service but many owners did not have a car/engine that ever achieved high levels of driving distance. When the interstate system was opened up with actual roads vs trails across the farm lands that all changed.

Tom V.

[Kenth]

Sometimes a picture is worth a thousand words.

A "gas" hose is perfectly fine for the PCV valve. If Pontiac used one from factory, you can too. You may shorten yours some though.
The fuel hose should be shortened and routed in front of the thermostat housing (needs to be turned as said before) and kept away from engines hot parts.

Also, there can never be vacuum above the carburetor, only atmospheric pressure, which on its way into the void (vacuum) below the throttle plates draws the crankcase fumes to combustion.

[Schurkey]

Originally Posted by Tom Vaught

they came up with a "Road Draft Tube system to remove the corrosive gases in the oil pan and valve cover(s) as the engine was going down the road.

The systems worked well except they put these corrosive gases into the earth's atmosphere.

True, but not the worst of the problem.

The draft-tube put oil mist in the center of the traffic lanes--dangerous as hell to motorcycles and narrow-track cars; dangerous to everyone for the first few minutes of a rain shower, when the oil would float on top of the rainwater, but before the loose oil floated into the sewer system and then into rivers and lakes.

This was all easy enough to see on concrete (white-ish) pavement. It was tougher to see on blacktop roads (depending on the condition of the roadway.)

People died due to draft-tube oil on the roads.

[Formulajones]

Thing is, even with road draft tubes rarely seen anymore, you still have oily center lanes from cars leaking. Guess where they leak.....in the center of the lane.

Pretty much any highly traveled road you can see the dark centers even today, and motorcycles still straddle the center because of it.

I don't see road draft tubes as the main cause here.

People dying from draft tubes...........lol that's a stretch.

[Tom Vaught]

Originally Posted by Formulajones

Thing is, even with road draft tubes rarely seen anymore, you still have oily center lanes from cars leaking. Guess where they leak.....in the center of the lane.

Pretty much any highly traveled road you can see the dark centers even today, and motorcycles still straddle the center because of it.

I don't see road draft tubes as the main cause here.

People dying from draft tubes...........lol that's a stretch.

People die from many things on the freeways and secondary roads, and streets today.
People Drunk, people on drugs, people falling asleep and running over people stopped at intersections, people plowing into people on a congested street.

Plus in the road draft days there were many millions less cars and trucks on the roadways. Pontiacs on the road with open breathers and other oil leaks
put down oil on the center of the lanes too. So you are both right.

I was referring only to the durability of the engine in miles being increased greatly.

Tom V.

[steve25]

Yes, your water outlet IS backwards and worse then that it looks like it’s pinching off that hose!

Also fuel line as it looks like in this photo is not PCV hose since when it’s hot vacuum can suck it closed.
You need either a breather in the passenger valve cover or better yet the original tube plumbed to the air cleaner.
This original tube to the air cleaner vents the crankcase at high throttle openings when there is little to no engine vacuum to work the PCV system, but there is vacuum above the Carb at those times.

[Skip Fix]

My old Chevy 409s had a road draft tube out the back of the intake with a big baffle system riveted to bottom of intake.

[steve25]

Excuse me, I should have used the term pressure differential to make my discription more pleasing to some here!

[66sprint6]

Thanks for the info, guys. I figured that there was somethng needed to allow air in, but I didn't think that it would be a push in breather in '74.
Here's the air cleaner that came on the engine. Who knows if it even belongs to the engine, which of course has an aftermarket intake anyways. But in looking at the housing, there is an inlet for a PCV hose. But it looks like there's just a little rubber insert to direct flow. In any event, is it always oriented to the passenger side? And what's the configuration at the valve cover? A grommet with a hose or a push in cap that looks like the breather that the hose attaches to?

[lust4speed]

Grommet hole in air cleaner doesn't have anything to do with the PCV. This is where the vent tube we mentioned earlier terminates from the valve covers. Since '67 engines did not have the pre-heat hose coming from the exhaust manifold and this air cleaner snorkel has the fitting for the large hose, I'd say that it did come off the '74.

A few years back I sold a '70 SBC 327/350 block that still had the casting hole for the draft tube at the rear of the block but was closed off with an expansion plug from Chevy. Surprised me that Chevy was too lazy or cheap to clean up their molds seven or eight years after they stopped using draft tubes. One of the really good ideas was getting rid of the draft tube. If you watch early movies of the freeways in Los Angeles you can see quite a black ugly buildup in the center of the lanes. I remember riding motorcycle in the 60's and learned really quick that the center of the lane was a slip and slide because of all the crap coming out of that tube. Still SOP today to stay out of the center, but not nearly as bad.

[66sprint6]

So I've been doing some research since I started this thread and found the parts needed to put it back to factory. In doing so, it seems that this air cleaner base is from a '77-'81 Trans Am with the 403 Olds engine or similar It's just missing the part on the end of the snorkle for the fresh air hose.

https://www.firebirdcentral.com/Prod...tCode=ENC-2457

https://www.chicagomusclecarparts.co...77-79-trans-am.

I'm wondering if the grommet will fit the valve cover on this engine, though. Like I said: hodge-podge.

[Formulajones]

......A few years back I sold a '70 SBC 327/350 block that still had the casting hole for the draft tube at the rear of the block but was closed off with an expansion plug from Chevy. Surprised me that Chevy was too lazy or cheap to clean up their molds seven or eight years after they stopped using draft tubes.......



Just an FYI

Chevy wasn't too lazy or cheap to change the mold. That draft tube location was still used in some applications with a fitting and PCV valve installed in that draft tube location up through 1970. Some other applications plugged it when the PCV was put in the oil fill tube at the front of the engine.
Wasn't until late 69-ish when the 010 block started circulating that went away and started using a different PCV setup.

[aceaceca]

What you have there is a thermal air cleaner. If you install it with all the correct
pieces you have other things to check to ensure it works as designed. In the snout of the air cleaner there is a flap valve controlled by the temp sensor and a
a vacuum solenoid. On cold start up warm air passing over the exhaust manifold is fed to the carburetor from the under side of the snout. This enables a leaner choke setting. As the engine heats up the temp sensor warms and allows vacuum to be applied to the vacuum motor on top of the snout. This opens the front entrance to the air cleaner snout while simultaneously shutting off the warm air feed. If these components are not hooked up and operating correctly
the engine could be fed hot air only , heated by the exhaust manifold. That is, the flap in the air cleaner does not open. I have seen cars scrapped or donated that would not pass smog check solely because the air cleaner was not operating correctly.

[389]

Run a hose from the air cleaner, make sure its on the filtered air side. Then run that hose on the passenger side valve cover.. I like this set up best...

[dataway]

Also .... looks like either the wrong alternator belt, or upper bracket ... lots of room for adjustment in one direction, not much in the other

[66sprint6]

I don't believe that I'll use this air cleaner housing. The PCV hose will be on the drivers side and I don't know if the parts needed will work with the Pontiac valve cover. The Olds covers look more angled.
I see that these air cleaners are somewhat desirable and there's not many out there. So maybe I'll sell it and get a proper set up.