Road Draft Tube

Road Draft Tube

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By Outlaw56 - 15 Years Ago

I have read a lot about converting the road draft tube from the side of the block to the back of the valley cover. From the valley cover, the road draft modification is routed thru a pvc valve and into several options to include base of carb or intake. Would this not just route a lot of contamination into the intake? It makes sense to get rid of the mess created by the road draft tube, but not to vent it into the carb or intake manifold. What am I not understanding? This inquiry is not about how to do the modification, but rather why its done this way.

Darrell Howard

Whitefish, MT Outlaw 56

By mctim64 - 15 Years Ago

PCV valve is an emission control device, back in the day a road draft tube was all you needed to clear the engine of the gasses that build up. The EPA does not like it when anything like raw fuel or oil is vented directly into the atmosphere. So with the PCV it is directed into the engine to be burned and then to the atmosphere. I have found that the PCV is not enough in the Y, at high RPM and full throttle there is no vacuum, so I still run a road draft tube along with a PCV valve.

By crenwelge - 15 Years Ago

Back in the 50's when we still used gas powered trucks, we ran a hose from the road draft to a hole cut in the top of the of the air cleaner with no pcv valve. Vacuum goes up at the top of the air cleaner at higher rpm's even though manifold vacuum drops to nothing. I don't remember if this was offered from the factory but there were after market kits. Back in those days it was common for a truck to drop down to 10 mph while climbing a hill and of course cabs were not very air tight. Without this type of ventilation a driver would get tears in his eyes from the fumes. The ventilation eliminated it completely.

By DANIEL TINDER - 15 Years Ago

With a T-Bird style draft tube/PCV combo, mixture dilution/excessive crankcase pressure at high RPMs might be avoided, but majority running time with normal, high-manifold-vacuum cruising would allow unfiltered crankcase air supply, since the more restrictive filler-cap air filter would likely divert the manifold vacuum/PCV supply flow ? Keeping corrosive fumes flushed out of the crankcase will prolong oil/engine life, but isn't replacing it with dirty air is sort of like; two steps forward-one step back?

By crenwelge - 15 Years Ago

The blowby is really not that dirty. It is laden with an oily mist that actually seemed to keep the carbon off the intake valves.

By Ted - 15 Years Ago

Outlaw56 (2/25/2009)

This inquiry is not about how to do the modification, but rather why its done this way.

The road draft tube concept was effective but not without problems of which the more significant would be emission deposits into the atmosphere as well as placing a large amount of oil on the roadways. The oil on the roadways was not only deemed a hazard for driving but a concern to the environment as enough oil was being deposited to make its way into the soil and waterways. The incorporation of the Positive Crankase Ventilation (PCV) system in the early Sixties provided a simple and effective solution to the aforementioned problems. Most PCV valves will move approximately 3 cfm of air during normal driving and up to 6 cfm of air under higher load conditions. PCV valves are tailored for specific engine combinations (usually by cubic inch) and as such, care must be taken when retrofitting these valves to engines not originally equipped with PCV systems in that the sizing of the PCV valve must be considered. A side benefit to the PCV valve system is that the crankcase is under a light negative pressure during cruising which in turn minimizes oil leaks that would be present otherwise. Utilizing a road draft tube in conjunction with a PCV valve negates many of the benefits of using a PCV system.

By Outlaw56 - 15 Years Ago

So if I were to use the original road draft tube AND a PVC valve, here is my question. The valley cover I have is for a 256 Yblock. It has a fitting on the back which appears to be for a PVC Valve. I am installing an Edelbrock Thunder Series Carb. The front of the carburetor has a port that is labled "Manifold Vacum Signal" for PVC valve. Is this where I would make the connection from the valley cover to the carburetor with the pvc valve somewhere in between? Not sure what Edelbrock is talking about when they refer to "Manifold Vacum Signal". I also have the option of hooking up dual fuel feed fuel input to each side of the carburetor, but I do not think this engine really needs that option. Nay ideas what purpose a "dual feed" carb would serve?

Darrell Howard Outlaw 56

By oldcarmark - 15 Years Ago

The opening in the valley cover will take a grommet which you can buy at most auto parts stores.Measure the diameter of hole and get the correct size grommet.The PCV valve goes into the grommet and then run a fuel line type hose from it to the fitting on carb.Make sure the oil filler cap is clean and that air can be drawn in through it.If you really want to do a closed system get a cap with hose fitting on it and run hose to air filter.You can plug the hole in side of block where draft tube was using a frost plug and grinding a flat spot on each side where the bolts can hold it on block.Thats how I did my 56 292.The dual feed option is for high performance use where you need a constant supply of fuel quickly to feed the primary and secondary fuel bowls instead of feeding the secondary bowl from the primary with the transfer tube.

By miker - 15 Years Ago

I was told that the PCV system was originally use on milk and ice delivery trucks, as they didn't put on enough high speed (25mph) miles is the city to make the draft tube work. Some of still drive like that due to traffic. I did a PVC on an older car, and didn't provide enough intake air under heavy vacuum (from the oil fill tube on a Y block, or a plugged oil fill cap), and on a long downhill stretch with high manifold vacuum, I sucked one valve cover gasket into the motor, and then spilled oil all over the exhaust manifolds. Makes a lot of smoke. Not enough PCV valve and hose will blow them out, so pick a valve from a like sized motor. You should also consider a baffle on the valley cover, I had one motor pick up enough oil off the dist. gear to get it into detonation (it was a blown motor), and take out the head gaskets. Still, I run closed PCV's on both my Y's, and also on the old scrub.

By Ted - 15 Years Ago

Outlaw56 (2/28/2009)

So if I were to use the original road draft tube AND a PVC valve, here is my question...........

I did the same as Mark as I simply put an expansion plug in the road draft tube hole of the block when I installed the PCV system. I did cut the small oil drain tube off of the road draft tube assembly and reinstalled the modified assembly back on the engine for appearance purposes only as the road draft tube itself is totally non-functional now.

Doing a search on this site regarding road draft tubes comes up with an inordinate number of queries around the oil leaks from these tubes and that alone is enough to warrant getting them off of the engines or making them non-functional as I did.

By MoonShadow - 15 Years Ago

I've looked at the VW oil block off plates (that will fit the block where the draft tube is now). Most of them have a threaded bung in the center. I wonder if a PCV valve could be placed down there or would it pick up oil splash. Also, along the same Idea to run a hose from there to the Air cleaner? Any thoughts? Chuck in NH

By Outlaw56 - 15 Years Ago

Lots to think about here and from lots of experience dealing with the thoughts behind modifying, replacing, or combining a PVC System to function with an original or modified road draft tube. I need to confirm I have this correct. If I want to install a PVC system, I am thinking the "closed system" would be a good choice. Again, if I understand correctly, this can be accomplished by using a valley cover that will accept a PVC fitting. From the PVC fitting, run a hose to a vacum port on the carb. To close the system, use a non/vented oil fill breather cap with a port to connect an air line from the oil fill cap to another port installed in the bottom of the air cleaner?

This would close the system, providing the oil fill cap is not a breather. I am waiting to see how the question regarding a PVC fitting to replace the road draft tube in the side of the block is answered. I have never heard that option disucssed.

Thanks for all the information and help.

Darrell Howard Outlaw 56

Whitefish, MT

By MoonShadow - 15 Years Ago

Me niether! It's just something I noticed while looking at the VW block off plates. Chuck

By Hoosier Hurricane - 15 Years Ago

Chuck:

Think about it. How common are leaks in the draft tube area on the side of the block? Must be a lot of spash there. I would think a pcv would suck up a lot of oil, and if you put a hose to the aire fileter, and there was a slight vacuum in the air filter, it may even suck oil through the hose and directly into the air stream. I don't think you want that either. And if you're referring to your blown car, pressurized air blowing down that hose into the crankcase isn't a very good idea, you want to get rid of crankcase pressure, not increase it. Just my humble opinion.

By miker - 15 Years Ago

You're correct about the crankcase pressure, but the PCV valve should close under pressure or a backfire. That's to prevent a crankcase explosion if you've got a lot of fuel contamination. I've never had that happen. I have been concerned about moving all the crankcase pressure out of the hose from (in my case) the oil fill tube to the suction side of the air cleaner, but I'm not getting a lot of oil in there. And I haven't blown the gaskets out of the valve covers or the pan. Probably because a street car doesn't spend that much time under boost, but the dyno pulls weren't a problem either (till the head gaskets went from the load of oil when not under boost) through the PCV valve. I had a high mileage factory turbo car, and we found a lot of oil in the intake, pulled the turbo and had it gone through, and was told the seals were ok, it was blow by. I know some racing motors run crankcase evacuation systems, but I've never had anything that extreme.

By MoonShadow - 15 Years Ago

Thanks John. No I wasn't thinking about it for mine with the blower. It was just a thought I had. I was concerned about the oil splash from the begining. I'll stay with my current PCV setup. Chuck in NH

By rexbd - 15 Years Ago

Hope this isn't stupid. Are you better running a PCV valve from a larger displacement engine, such as an FE series, to adapt the Yblock to maximize flow from the valve? Confused about if its better to vent the valve cover breather into the air cleaner or doesn't matter for a street car.

Hope to have body done in the spring and tear the engine apart this summer with goal of cruzin this fall. Getting closer.

By Ted - 15 Years Ago

rexbd (3/3/2009)

Are you better running a PCV valve from a larger displacement engine, such as an FE series, to adapt the Yblock to maximize flow from the valve? Confused about if its better to vent the valve cover breather into the air cleaner or doesn't matter for a street car.

Always run a PCV from an engine that's similar in cubic inch when retrofitting. But Y's did have PCV valves in the early Sixties so that would be the one to work with first. When retrofitting for a Y, I simply pick out a PCV valve originally designed for a 289 or 302 SBF. And if given the choice, run the vent to the air cleaner. Just makes everything cleaner.

By Outlaw56 - 15 Years Ago

Ted,

I have a Ford Race Filter that has the element exposed on the sides. Where would you suggest porting the hose from the PVC to come into this type of air cleaner?

Thanks,

Darrell Howard Outlaw 56 F-100

By oldcarmark - 15 Years Ago

I think what Ted meant was run the hose from air cleaner to the oil fill cap to create a fully closed system as opposed to just drawing air through the oil cap.The hose from PCV valve ideally would go on the port on carb if there is one on carb.Do not hook it in at back of manifold as rear cylinders will run lean.If there is no port on carb you may have to drill and tap for a vacuum fitting as close to the carb as possible or use a spacer plate with PCV hose fitting incorporated in it.To make it a closed system using your type air cleaner put a vacuum fitting in bottom of air cleaner inside the filter element.That way you draw filtered air into cap and any fumes from cap are drawn into air cleaner and burned in carb.

[Note added by Ted / 3/5/2009 7:30PM] Thanks Mark. That is indeed what I meant.

By 2721955meteor - 8 Years Ago

on my 57ranchero i drilled a capscrew and welded a fiting to adapt a hose then a pcv valve from a 351,capscrew went into the ds head axcessing the push rod hole, then to the bace of the holley 4v. i left the original .road draft(left front of the block) iget some air frome the filler cap,balance from original rd tube. no leakes ,did this as got the od whif of blow by after a long run.my project started as i wanted pcv valve ,but did not want to remove the int and mod the valley cover. will eventialey redo with the proper ,or mod the existing one.Iwas concerned i would pickup oil as get lots to the rockers and pluged the bleed tubes.litle or no oil gets by pcv,and no negitive vacume in crankcace.
never smell blow by ,does not use any oil.the engine has aprox 70000 miles with rebuilt heads andholley 4v aswell dura spark ign runs like a charm

By olepoop - 8 Years Ago

I don't want to start a new issue with the road draft tube. Mine would push out a quart of oil in 20 miles oiling the whole under side of truck. 272 bored to 292 and fresh. Put on a evac system thru valve covers and hosed to the collectors on headers. I have oil pushing out fuel pump and leaking out pvc valves on headers. So I still have an issue.

By charliemccraney - 8 Years Ago

That style of evacuation system is only effective on racecars that see high rpm. It won't solve your problem and will probably cause more.

A quart in 20 miles seems like a bad valve cover gasket, oil filter gasket, oil pump gasket, something like that. You sure it's coming out of the road draft tube?
If the road draft setup was clogged, then your crankcase will pressurize, which can force oil out of many places and the evacuation system you have installed will not help that when used in a street vehicle.

By DryLakesRacer - 8 Years Ago

I installed a lot of PVC "smog " devices in So Cal in 62-65 when I worked fo Sears. We ruined countless rocker covers and put plugs in road draft tubes. My 56 is starting to show "breathing" from the road draft tube but it is dry with no drips at all or smell I can detect. I am assuming every open engine would show something unless you've installed Total-Seal piston rings. (Ted is this a good idea for street engines?)

I have the rear breathing valley cover ready to go which I would refit with a PVC. Personally a PVC is not a bad idea both for the environment and to keep your engine clean since you are running under a slight vacuum. The test at Sears was a device we set on the filler cap that showed a vacuum by a ball moving. I would slide a piece of paper over the tube and if it stayed they even under reving the engine it was good. A poor condition engine under reving would not hold the paper because of too much blowby. If I ever need to remove my intake I'll probably do it.

By Ted - 8 Years Ago

olepoop (5/7/2016)

As Charlie brings up, header evacuation systems are specifically for race cars running open headers. On the race cars, these systems by design remove air from the crankcase which reduces the drag on the crankshaft and other moving parts. These system still incorporate a check valve at the header collertors to eliminate any possibility of any backpressure making its way back into the crankcase.

Vacuum systems that use the exhaust flow as the flow driver are typically non-effective in daily driver situations when hooked up to an exhaust system that has mufflers or long small diameter pipes. This is simply due to any back pressure present reducing the negative air pressure flow across the installed nozzle and subsequently prevents a vacuum or negative pressure from being generated. These types of vacuum evacuation systems are ideally suited on open headers that have no mufflers and as a result, these systems do work well on the racing applications. Here’s a picture of the evacuation system on my roadster.

By Ted - 8 Years Ago

DryLakesRacer (5/8/2016)

My 56 is starting to show "breathing" from the road draft tube but it is dry with no drips at all or smell I can detect. I am assuming every open engine would show something unless you've installed Total-Seal piston rings. Ted is this a good idea for street engines?

I typically only use gapless rings on those applications where I’m minimizing the contaminants getting into the oil. Supercharged with injected alcohol is one of these applications. On a street car, I typically don’t recommend gapless rings simply due to the lack of oil that can get past them thus increasing the wear factor. I did run a Ford 427 High Riser on the same set of gapless rings in excess of twelve years and to their credit, those rings were still sealing good at the end of their reign. The heads were thoroughly worn out at that point though but simply due to lots of running and nothing to do with the gapless rings. The cylinder walls were also heavily scalloped but that had more to do with the thin wall casting design of the 427 side oiler block and the 0.009” piston wall clearance and not the gapless rings.

By Bill Childs - 8 Years Ago

Been following this thread with interest trying to sort out a pcv plan. Check out this pic of what I have here:

I think the fitting I have on the aft end of the valley cover came with the Mummert intake. If I want a closed pcv system should I stick the appropriate size pcv valve inline between this fitting on the valley cover and the hose barb coming of the back of my carb? Or the threaded hole in the boss on back side of the intake? I'm thinking carb.
Also, then I get an oil fill cap that has a tube for a hose and run that into my air filter? Am I close with any of this? Thanks

By miker - 8 Years Ago

Short answer, yes. I'm using a PCV valve very much like your fitting in the valley pan. Goes into a grommet, and a hose to the carb fitting. I've used the manifold fitting like you show, also.

One of my cars has the closed cap, running to the a/c. The bird has a finned valley cover and I used the fill tube off a 69 Camaro. Sealed cap (looks like a radiator cap) with a bung for a fitting to the a/c. The OEM application was a PVC that screwed in there, I used a barb.

One caveat. The original valley pan didn't have a baffle, and I used a Moroso grommet with a "duck bill" design, to limit oil flow. When I built the new motor with the high volume/pressure oil pump, it didn't control the spray coming off the dizzy drive. That was a blower motor. Blew the head gasket on #7 twice before we realized the oil contamination was the likely cause. Welded a proper baffle under the valley cover, no more problems.

By DryLakesRacer - 8 Years Ago

Bill C that's correct. Most forget that the PVC valve is a flow device so the vapor it is sucking out of the engine is actually thru the engine and it should be filtered air. If you remember many GM cars had that filter inside the air cleaner but outside of the carb air filter and is an easy one to add. Many of the early PVC valves were threaded and I have one of those 69 camaro fill tubes withe sealed cap where you would place the valve. If that style is used however there should be a breather cap on one of the valve covers with a hose up to a filter also that's how they (GM) did it. Good luck and I like what you've done so far..

By 57RancheroJim - 8 Years Ago

Bill Childs (5/11/2016)

Been following this thread with interest trying to sort out a pcv plan. Check out this pic of what I have here:

I'm using the same set up as yours. I have the PCV valve inline between the valley cover and the carb. To use the manifold fitting would have required a large loop of hose to avoid sharp bends and kinks, going to the carb allowed a shorter hose with a smaller loop. I also use a filler cap with a hose going to the air cleaner.

By Bill Childs - 8 Years Ago

Great info! Without changing my oil fill tube, is there a good aftermarket cap with the hose fitting available, or a specific old one that will seal and do the job? Also, which inline pcv valve are you using Jim?

By 57RancheroJim - 8 Years Ago

Bill, I wish I could be more helpful but the system I have was salvaged off another engine, I believe it was a 1962, I got the valley cover with the PCV and hoses and the filler cap from it. Macs has a similar cap listed for trucks, there maybe other places to get them.
http://www.macsautoparts.com/ford_truck_late/ford-pickup-truck-oil-filler-breather-cap-painted-push-on-type-with-spout-292-v8.html

By Dobie - 8 Years Ago

A filler cap for a late 70s/early 80s Chrysler 318 may fit and it has the nipple for the connection to the air cleaner. I know they fit the filler tube for late late model flatheads and it looks like the y-block tube is the same diameter.

By DryLakesRacer - 8 Years Ago

Stant 10070. I believe it is chrome. A Scotch Brite pad and some semi gloss should make it look stock if that's what u are looking for. Good luck. Show us photos when it's done.

By Bill Childs - 8 Years Ago

Stant SO-70 is the painted version and exactly what I had in mind. Got the number from Jim's link then found a guy who has some NOS for sale on eBay. $9.99 including shipping. Now to locate a suitable pcv valve. Thanks guys.

By 57RancheroJim - 8 Years Ago

This is the type I have, a little more pricey, Didn't think to look at Ebay for an original..
http://www.ebay.com/itm/New-63-72-Ford-Oil-Filler-Cap-Closed-Emission-Fairlane-Galaxie-F100-Motorcraft-/321966990351?fits=Year%3A1962|Model%3AF-100&hash=item4af6ba640f:g:uUUAAOSw0QFXDE1~&vxp=mtr

By Bill Childs - 8 Years Ago

Just searched ebay again and found two different style caps with the same Stant SO70 number. Here's the one I got. Seller still has 8 of these NOS caps.

http://m.ebay.com/itm/STANT-SO-70-OIL-FILLER-CAP-NEW-OLD-STOCK-/272088359437?hash=item3f59bae20d:g:ABwAAOSwgQ9Vo8d5