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Some Folks Don't Have Vision!
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On my 52 Flattie, I noticed (um, how could you miss it...) the road draft tube. What exact purpose does it serve and is it really a necessity when rebuilding. The reason I ask is that I have an earlier Edelbrock performance manifold without said tube and would like to use it, if possible. However, I don't have any qualms about getting a correct year manifold with the road draft tube casting if it's really needed. Can anyone shed some light on this one? Thanks!
 

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RodGuyinCO said:
On my 52 Flattie, I noticed (um, how could you miss it...) the road draft tube. What exact purpose does it serve and is it really a necessity when rebuilding. The reason I ask is that I have an earlier Edelbrock performance manifold without said tube and would like to use it, if possible. However, I don't have any qualms about getting a correct year manifold with the road draft tube casting if it's really needed. Can anyone shed some light on this one? Thanks!
It boils down to a simple rule of thumb - air in should equal air out. An engine is nothing more than a big pump. As each of the pistons goes up it produces vacuum (or pressure, depending on which side of the piston you are looking at). Since nature doesn't really like a vacuum, air rushes in to fill the void. If it can only get in one side, you tend to have a problem or so. Eventually you will have significant oil leaks and will start burning oil as the rings will not seat at the bottom and push oil onto the cylinder walls - even the older 4 ring flatties. Soooo, to have a good flow, you need a vented cap as well as a road draft tube - when the car is in motion, the air flowing by the tube is supposed to create positive flow - cap, thru the engine, then out the draft tube. Just make sure you do have some sort of filtration on both - originally it was nothing more than a wire mesh screen, but something better can be designed and keep more of the airborne crud out of the engine that seems to clog up flathead valve galley and pan.

I hope this is clear - if not, give me a response post and we'll try to figure it out.

Dave
 

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russlaferrera
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road draft tube

My understanding it is used to let the engine breathe. Air goes into the engine Thu the oil cap (thats why there is a filter mesh inside the cap) into the engine. The draft tube is cut at an angle to create a draft (vacuum) and pull out the fumes....russ
 

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aka Duke of URL
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russlaferrera said:
My understanding it is used to let the engine breathe. Air goes into the engine Thu the oil cap (thats why there is a filter mesh inside the cap) into the engine. The draft tube is cut at an angle to create a draft (vacuume) and pull out the fumes....russ
Correct. The system ventilates the crankcase to remove excess blow-by fumes. If not ventilated properly, the blow-by will combine with water vapor and form sulfuric acid and also cause the formation of sludge along with associated dire results to metalurgy.

Also without proper venting, there is no release for the blow-by pressure and it will start to blow out seals and gaskets.

The PCV System replaced the ROAD DRAFT SYSTEM.
 

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Troll Hunter
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I have built a couple flatties in the last few year and have great luck with plumbing a PCV system through the old road draft tube hole. I prefer a PCV system and others don't, but I feel it makes for a better running and cleaner engine... just my.02.
 

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Some Folks Don't Have Vision!
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Discussion Starter #6
Thanks, Guys!

Appreciate the info. :thumbup: I kinda figured that's what that tube was all about. I think I might try the PCV plumbing trick. It's probably a whole lot less unsightly. I do kind of wonder how the pre-49 flatties breathe since they don't have the draft tube...sigh-I've got SO much to learn. :drunk:
Thanks again and I'm sure I'll have more flattie questions as I start to pull this little jewel apart.
 
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