Using road draft tube for PCV

R

runmikeyrun

Senior Member
Hi guys!

I would like to modify our Y block to a PCV system. Trouble is, I’m not in a position to make extensive modifications; i.e. changing valley pan, drilling holes in the valve covers etc. Since the truck does live a decent part of its life going 5mph in parades I know the draft tube simply isn’t pulling any vapors out of the engine at that speed.

I’m wondering if I can use the existing road draft tube setup with a PCV valve, and run that to the port on my Holley carb. Ours has the draft tube at the front of the motor, left side, down near the bottom of the block.

I’m thinking of sealing the bottom of the draft tube, and putting the PCV valve into the side/top of the removable canister. I think the oil can still drain back through the hole into the block, and an oil separator would catch any excess. I’ve halfway convinced myself that it would just pull way too much oil out of this type of setup, so if my suspicion is correct just tell me and I will scrap my plans.

I know that proven PCV conversions are the best option but I’m not in a position to take any parts off the motor since this truck belongs to the department I work for. I’d just like something that works better than the road draft tube to help increase longevity.

For what it’s worth I have cleaned the draft tube filter and also cleaned the oil filler cap so the engine can breathe.


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You could leave the road draft tube as is to serve as the fresh air intake for the PCV setup, then fabricate an oil filler cap that is airtight except for a hose fitting to connect to a PCV valve that in turn runs to the fitting on the carb. This way you won't have to worry about pulling oil into the PCV system. Air entering through the road draft tube gets filtered by the filter element in the draft tube housing, and that air coming in keeps oil from getting out. No worries about sucking oil out of that filler tube sticking way above any splashing oil.
 
You can still buy an oil filler cap, sealed, with a hose fitting on the side of it. An in-line PCV valve to the carb base or an adaptor carb spacer would do that. Some 69 chevys used an oil fill tube with a bung for the PCV and a sealed cap (I’ve used them on my y blocks). Probably not the best, but better than a parade car with draft tube.

Sucking oil out from not having proper baffles is only a high rpm problem in my experience.
 
Runmikeyrun: I took off the complete draft tube off my 56 312 Ford, fabricated a plate to cover the hole, drilled and tapped a hole in the plate to accept a i/2" fitting and used a rubber tube to connect the vacuum from the base of the carburetor to the fitting. I put a PCV valve used on a 2000 V-8 Mustang in the line near the fitting. (The PCV valve must be mounted horizontal rather than vertical, which limited my choices of were to mount it.) I've had it in place for 4 years with no oil leaks, no PCV valve sticking, and a very clean running engine.
 
Those are great ideas guys, thanks! I’m going to take all of that into consideration and look over the motor in the next couple days to see what makes the most sense aesthetically etc. Thank you!


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Ok, I have an idea.

The bolt that is right next to where the coolant sensor enters the head goes down to the valley chamber. I’ve seen threads that people have the bolts missing and oil vapor coming out.

Any reason I couldn’t plumb something together with a PCV valve to thread into that hole?


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That bolt hole to the rear of the temp sensor should have a 5/16 thread and goes into a pushrod opening. It often has a sparkplug wire bracket and the battery ground cable bolted to it.

If the engine in question isn't already using that hole, there might(?) be enough wall thickness on a short-ish piece of 1/4 inch pipe to cut it to 5/16 bolt thread then attach some hose to a PCV valve. The PCV setups I'm used to seeing usually have a larger inside diameter though. Not sure how effective it would be.
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dmsfrr said:
That bolt hole to the rear of the temp sensor should have a 5/16 thread and goes into a pushrod opening. It often has a sparkplug wire bracket and the battery ground cable bolted to it.

If the engine in question isn't already using that hole, there might(?) be enough wall thickness on a short-ish piece of 1/4 inch pipe to cut it to 5/16 bolt thread then attach some hose to a PCV valve. The PCV setups I'm used to seeing usually have a slightly larger inside diameter though. Not sure how effective it would be.
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I think I’m going to give it a go then. A lot cleaner than the oil filler cap bung/hose and simpler than making a plate for the draft tube opening. Everything will tuck right behind the air cleaner. Thanks for the heads up.


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Still going to have to block the road draft or oil cap if you don't want fumes. PCV will just be sucking air from what ever is easiest place. If it's more blowby than valve can handle it is still going to come out somewhere. Best for no fumes would be like later trucks for PCV and the filler vented into air cleaner housing. I think the cars sent to California in early 60's had it too.
 
5851a said:
Still going to have to block the road draft or oil cap if you don't want fumes. PCV will just be sucking air from what ever is easiest place. If it's more blowby than valve can handle it is still going to come out somewhere. Best for no fumes would be like later trucks for PCV and the filler vented into air cleaner housing. I think the cars sent to California in early 60's had it too.
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I’ve seen the setup you’re referring to. I figured I would block off the road draft tube inside the canister so I could keep the stock look and leave it in place. That way it will draw fresh air in through the cap. I cleaned the cap out with acetone and repainted it a few weeks ago so the material inside is clean and air can flow freely. I have a Holley with a PCV port to connect to the valve. That should give me an acceptable path for air to circulate, correct?


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It should unless the engine is very tired. I'm not a Y block expert by any means and have not been around one for years, but that's the way PCV works on most any engine.
 
Sounds good. The engine has been in service ever since it was transplanted in, but hasn’t seen many actual miles. We all know that sometimes no miles can be worse than high miles. It runs good though, so for now I’m doing my best to maintain that and hopefully prolong a rebuild until after my career is finished lol.



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runmikeyrun said:
I would like to modify our Y block to a PCV system. Trouble is, I’m not in a position to make extensive modifications; i.e. changing valley pan, drilling holes in the valve covers etc.

Since the truck does live a decent part of its life going 5mph in parades I know the draft tube simply isn’t pulling any vapors out of the engine at that speed.
Click to expand...


Does the engine expel fumes from either the oil filler breather or the crankcase ventilation tube? Does the tube drip any oil?


THEORETICALLY ... :rolleyes: ...

The way the tube outlet is angled at the bottom, it creates a partial vacuum at speed allowing it to draw blow-by from the crankcase (also considering an unrestricted fresh air inlet and the system has been maintained properly and the engine does not have excessive blow-by).

FORD also states that there is a partial vacuum created while standing still as a result of fan wash.

IMO, the modification you are describing will not ventilate the crankcase properly. Even the later Y-Block PCV System used by FORD was not all that effective. It was just a stop-gap measure until design improved (design progression) in later years (again IMO).
 
KULTULZ said:
Does the engine expel fumes from either the oil filler breather or the crankcase ventilation tube? Does the tube drip any oil?


THEORETICALLY ... :rolleyes: ...

The way the tube outlet is angled at the bottom, it creates a partial vacuum at speed allowing it to draw blow-by from the crankcase (also considering an unrestricted fresh air inlet and the system has been maintained properly and the engine does not have excessive blow-by).

FORD also states that there is a partial vacuum created while standing still as a result of fan wash.

IMO, the modification you are describing will not ventilate the crankcase properly. Even the later Y-Block PCV System used by FORD was not all that effective. It was just a stop-gap measure until design improved (design progression) in later years (again IMO).
Click to expand...



All very good info, thank you! However, given the circumstances that I can’t pull any parts off to do the valley pan or valve cover mods would my idea be more effective than leaving the road tube in place? My concern is the amount of slow driving we do in parades.

Thanks!


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I did this and it worked ok.
My 239 y block had bad blow by.
I put a pcv grommet in the road draft tube and a pcv valve for a 302 mustang, that’s what I had on hand. Then I ran a hose to the intake vacuum port.
All the fumes got sucked up and burnt.
I probably drove 3000km with that setup before upgrading to a 292.



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Larry Do you have any more information about the pcv valve used? A picture?

I was thinking about trying it.
 
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