SBC Experts! I need your advice.

I have a '76 350 and I would like to use the old Chevrolet script valve covers on my heads. What do I need to do to convert to the non-PVC style and still be able to put oil in the engine? Is it just a matter of changing over to an old style intake? Please, life can't be that simple...

 

Using the older style filler neck intake has worked for me...

BYC

 

You will also need to have some sort of crankcase ventilation, since the newer blocks don't have a road tube. With just the oil filler tube and breather cap, you will get some oil coming out of it, especially on the freeway. I run a sixties corvette tube with a non vented cap. This tube has access for a pcv valve. Moon breathers on both valve covers complete my setup.

 

Hatch... where would I look to see if my block has a road draft tube?? I'm thinking of doing the same conversion and I've got a 327 out of a mid 60s car.

 

The road draft tube comes out of the block right behind where the distributor comes up through the intake manifold.

JH

 

Here is an original GM engineering schematic I have in my SBC archive.

 

Check this thread - a couple of options presented here.

PCV Stuff

 

I ran old script valve covers on my 305. Obviously use an intake with the oil filler tube. To vent I drilled a hole in the pass-side valve cover on the top side in between the pushrods on #8 cylinder and attached a 90 degree fitting, running a hose to look like factory to the carb-mounted PCV. Seemed to work, looked very indescreet.

 

i threw an old stlye intake on,(with a oil filler tube),BUT i drilled and tapped (actually welded)a BUNG in the tube for the carb .... and it worked so NICE


and ACTUALLY some of the mid sixtys chevys came TAPPED for PCV valves already

 

Another suggestion if you do have the road draft tube hole in the rear of the block is,

Install a softplug in the hole, bored to fit a pcv grommit.
Use the original road draft breather under the intake, then install the pcv valve in the new grommit behind the dizzy.
I did this on my 283 and it works great. And because it's behind the dizzy and low, you don't really even see it.
Of course ya need to either have a fill tube on the intake, or breathers on the valve covers too.

On later model blocks, i've seen pcv's in the fill tubes, and i've also seen a hole bored into the intake at the rear in front of the dizzy, and a baffle tig'd under the hole to block oil from being sucked into the valve..
a little more involved, but it gets the job done.

Rat..

 

Educate me here folks. Im on small block numero uno.

Let me get this straight. Ive got a 75' no road tube small block with non vented valve covers. I used a filler type intake with vented cap on the top of the filler tube. I was assuming that this would be sufficient. Sounds like Im wrong? Please fill me in por favor.

I feel like Im missin something.
Thanks

 

With a later non-hole-in-the-back block, you could get away with just using an oil-fill-tube intake with either a vented cap, or a sealed-cap type with a bung on the tube to run to the PCV port on the carb. But all youre doing is providing a release for internal air pressure (blow-by,etc).
Chevys idea at first was to provide through the front tube and vented cap a point for fresh air to go in, circulate through the crankcase and get sucked out the back by the roaddraft tube. This was to reduce the build-up of crud inside the engine. Realizing that didnt do too much sucking, they replaced the roaddraft tube with a similar fitting routing a line to a PCV mounted on the carb port (the PCV meters the air going in so you dont get a complete lean-out condition). Next they realized they were sucking dirty air into the crankcase, so they put a sealed cap on the oil-fill tube, routed a hose from inside the air cleaner but above the carb to the rear fitting, and then ran a hose from the oil-fill tube to the PCV. What that did was reverse the flow of air thru the crankcase but now it was clean, filtered air. Eventually they decided 'the hell with it', get rid of the oil-fill tube and the rear fitting, put the oil-fill cap and the fitting for the hose to the air cleaner on one valvecover, and on the other valvecover route the line to the PCV. Now theyre routing air thru the crankcase in a sideways fashion.
See?!

 

OK. I read through both threads and still have questions.

Let's assume you connect a PCV valve between either the oil fill tube or the road draft port and the base of the carb. In the other thread, Dr J states that the PCV only works at idle and another circuit is required for high speed crankcase ventilation. What does the traditionalist who's concerned about the austere beauty of his engine do to solve this quandry?



Ed

 

[ QUOTE ]
OK. I read through both threads and still have questions.

Let's assume you connect a PCV valve between either the oil fill tube or the road draft port and the base of the carb. In the other thread, Dr J states that the PCV only works at idle and another circuit is required for high speed crankcase ventilation. What does the traditionalist who's concerned about the austere beauty of his engine do to solve this quandry?



Ed



[/ QUOTE ]

Someone's going to point out that the PCV valve works all the time so I will say it first, it does, to an extent, but it's purpose is to restrict the air flow so if you have any appreciable amount of blowby it's going to pressurize the crankcase and blow oil ut the weakest gasket or oil seal.
I have rounded up a couple of "old style" manifolds too and I will probably run a sealed cap on the filler, or run the PCV from the transmission vaccuum source just behind the carb to a hole I drill near it in the manifold that opens up into the lifter valley, and a PCV piped cap on the filler. Mopar slant 6's had the cap that fits Rocket engine's fillers, I don't remember the diameter of it but it might fit the SBC filler too.

Anyway, to copy the function of most GM engine systems you need a PCV valve going from some/any area open to the crank case to the carburetor below the throttle plates and another open breather hose going from any crankcase source, (could be the same source as long as it's before the PCV valve) to the carb intake airhorn, typically in the aircleaner base inside the air filter. This works to ways. at idle the air is sucked IN the hose in the aircleaner by way of the PCV valve drawing the air through the otherwise sealed engine, and at higher RPM when the crankcase is experiencing higher blowby" pressures the PCV valve plumbing is drawing in crankcase pressure AND the other vent plumbig is drawing pressure out of the engine and into the aircleaner into the carburetor airhorn to be cycled through and burned like any other air/fuel mixture.

You can make them as inconspicuous as your imagination lets you.

 

You do just what I did on my later block. With the intake manafold off, You can build a draft tube setup under the manafold, and drill a hole in the back of manafold for draft tube, with a small taped hole for a hold down. Bingo my later block dosen't blow oil anymore. I know it's old tech for a new motor, but we all do dumb things to get the look, and I was tired of a sock wraped around my filler tube.--TV

 

Does the presence of this mysterious object in my engine indicate I have the draft tube somewhere? Mid '60's 327...

 

Yes ,it does I guess.The can you´re pointing at looks to me like the inner end of the draft tube. My 62 Impala has one ,too. My 56 ( ´69 327) doesn´t have it, so I guess your block perfect for using closed valve covers and a tube type intake.

 

Got it.


Thanks.

 

Ya, that mysterious object looks very close to the one I made. But I ran mine out the back of the manafold.--TV

 

What that is is the oil baffle to try and limit the amount of oil to be puked out. That picture also indicates youve blown a head right off the block and scattered rocker-arms willynilly.
Yes, what DrJ points out is at idle the system draws air in at one spot, thru the crankcase, out at another spot along with blow-by, thru the PCV and down the carb. As rpms increase it still draws air out the crankcase thru the PCV, but reverses the air flow out the other hose as blow-by increases and sucks it down the carb at the air horn. That is called a 'positive-sealed system', the old vented cap/PCV is 'positive-open system'.

 

My 67 283 Elcamino had a factory PCV valve(first year I think) hooked up to a special fitting for a hose in the old road draft tube hole behind the dissy. Check with some Chevelle guys for the hose fitting. Then the front oil filler tube would use a push in breather to let fresh air into the valley.

 

OK. Last night when I couldn't sleep as usual, I got to
thinking about this whole crankcase evacuation mess.

What the hell is the PCV valve needed for?

Why can't I just put breather on the oil fill and run a line from my road draft port to the air cleaner.

Am I oversimplifying things??? What am I missing??? Dr J???



Ed

 

[ QUOTE ]


OK. Last night when I couldn't sleep as usual, I got to
thinking about this whole crankcase evacuation mess.

What the hell is the PCV valve needed for?

Why can't I just put breather on the oil fill and run a line from my road draft port to the air cleaner.

Am I oversimplifying things??? What am I missing??? Dr J???



Ed



[/ QUOTE ]

Yea, it'd work, but if you're going to do that, why not just leave it alone, stock?
Also, if your engine smokes enough to blow anthing at all out the draft tube at idle then it might not have anyplace to go with the throttle plates closed at idle with it venting above the throttle plates. so it'll come out the breather or could blow back out the wrong way through your air filter.
Just for the record, I'm leaving the draft tube stock on the engine in my Model A (HA series Ford Flathead 6)

Besides, it'll help "lube" and "rust proof" the undercarriage!

 

This is the path I will take. Thanks for the input Dr J.


Ed

 

Burndup looks like the hole in your block for the road tube has been plugged, maybe with freeze plug? Thats definitely a road tube baffle in the valley.
Old days parking spots om pavement in town always had greasy spots just about where road draft tube came down back of engine.

 

i have an l79 327/350hp putting together question i have is pcv in caped filler neck runs to rear of holley . anyone know were fresh air comes in?

 

Through the oil filler cap.

 

its a twist on with seal in it . looking for oridgenal locations

 

O.K., I checked my pockets & I found 2 cents... so I'll through it in; I've got a '63 327. It originally had a draft tube (which I wanted to eliminate along with the drips) on the rear of the engine next to the distributor. It still has the baffle canister under the intake manifold at the rear of the engine. The engine has a "breather" cap on the oil fill tube at the front of the intake manifold from the factory. The valve covers are the original non-vented type.
I went to NAPA and picked up a 42048 PCV GROMMET from the "HELP" section. It goes into the hole where the draft tube went. (It's directly connected to the baffle canister) I also picked up a 2-9210 PCV valve. It's a NAPA/Echlin part from off the shelf. It's a 90 degree piece. I stuffed the grommet in the draft tube hole, stuffed the PCV valve into the grommet. I connected the PCV valve to the carb base. The PCV valve is a simple check valve to encourage the crankcase to "breath" in one direction. This set up sends any oily vapor from the crankcase to the incoming air below the carb and the engine burns it along with the air/fuel. It's simple, it's clean looking and it works.

 

This pcv valve is installed on these OMC valve covers. The valve covers are exactly like Corvette valve covers without the Corvette script. The idea is actually from a article in Ol Skool Rodz magazine about 10 years back. There is a small baffle built on the inside of the valve cover.