The Stovebolt Site Forums The Shop Area Engine Shop PCV vs. Road Draft Tube for Daily Drivers

Have been using a PCV system on my late daily 235 now for 3 years, but begin to think of going back to the road draft tube system.

There just isn't enough manifold vacuum when driving on the freeway and climbing up the hills and mountains at 2500-3000 rpm.
At those rpm the throttle plates are pretty open and the manifold vacuum is very low - too low to suck out all the increased gasses and vapors from the crankcase at higher rpm.
When traveling for a couple of hours the oil vapors like to weep out at the dip stick tube, the distributor mount and the pcv tube mount on the valve cover.
This leaves more of a mess than the road draft tube dumping closer to the ground.

Another thought about going back to the road draft tube is that I don't want to introduce any crankcase vapors into the intake any more - it does create quiet a build up inside the combustion chamber already after 2 years of daily driving - hard to believe until you find yourself scraping off the oil crystals build up. Never seen this after over a decade of road draft use before the PCV system.

Maybe the PCV system was introduced back in the 60s, as many have said before, mostly for political reasons.
It just seems too ineffective and makes more of a mess inside and out the engine than the old road draft system.

So my questions to the daily and frequent drivers out there - what are your experiences and what system do you prefer?

Keeping the draft tube on my 261 just because it's unique and I like it. My truck is not a daily driver so a bit of smog is okay by me.

http://community.webshots.com/user/geezer

I don't have a problem with a road draft tube. I would, however, put a better filter on it.

The road draft tube packed with some loose stainless steel wool seems the way to go.
I leave the valve cover tube connected to the air filter for now, but if oil vapors still get pushed out up there from increased pressure, I put the filter breather cap back on.

Never again will oil vapors enter my intake.
Nothing like personal experiences and seeing the effect first hand.
Just makes no sense crusting up the combustion chambers.

So glad I realized this before running a fresh rebuilt 261 next spring...

This is interesting. I have also been planning on going with a PCV set up on the 261 I'm building. I always thought it was the way to go. Not by experience, but from what I've read here. If it's going to make a mess of my engine, I'll have 2nd thoughts.

Oh, like you I have been converted to PCV a few years ago by others who recommended and swore by it.
Nobody ever mentions the more than noticable build up already after 10K miles.

Both inner chambers had a little more build up than the outer 4, as they are closest to the pcv inlet on the manifold.
And that was WITH a filter before the manifold - most run PCV without any filter except on the inlet, like the 261 PCV ...

New rings and occasional driving may produce less build up over a longer time period and it may just appear like unburned gas build up.
As long as the engine runs at full temp for a while each time after warm up, harmful water vapor can evaporate, especially in humid and colder months.


I just hope others will find this post in the future and be warned.

Here goes one vote for the engine's well-being.
It tells me clearly to get rid of the P in PCV and stop the rebreathing non-sense.

I would find a air filter from a motorcycle or something that can be put on the end of the draft tube. A choreboy just doesn't have the filtering ability and doesn't stop small particles of dust nearly as well.

If it's not broke, don't fix it. If you are fixing it, fix it better.

I would stick with PCV for a daily driver.

The draft tube always sucks while you are moving, so you only need to filter the inlet, which is either the vented valve cover or a vented oil cap.

If you look at modern PCV systems they always have a breather to the air filter. This not only keeps the air going into the crankcase clean, it sucks whatever vapors the valve can't handle into the intake when vacuum is too low.

The way I would set up a PCV on a 235 is to use a PCV valve instead of a road draft tube, use a non-vented oil cap, a non-vented valve cover, and a hose with a baffle and a catch can to the inside of the air cleaner. (Look up PCV catch can on ebay, they use them in VW diesel engines to catch the scuzz that comes out of the PCV)

I hate the road draft tube on my 261- it belches fumes into the cab in stop and go traffic and I stink when I get to my destination.

The road draft tube only pushes out blow by gases - it can't suck in air. Pressure is always positive inside the crankcase without PCV.

Using stainless wool is mostly to prevent splashing oil to directly escape through the draft tube when the pressure increases.

Also the tube end is cut at an angle on purpose away from the driving direction.
Starting around 30 mph the crankcase gases get sucked out by the lower pressure air rushing by the angled opening.
The faster the speed the more gases get sucked out - exactly the opposite from a PCV system :rolleyes:

I'll have to disagree that the draft tube will not draw in air. Yes, the majority of the movement is out, but it does take in air also. Kind of one breath in, and two breaths out.

Yes, it was tied into the air intake to reburn the gasses, but it was also to filter out smaller particles of dust.

I still believe that a better filter is needed. If anything the draft tube should be lengthened. If you were to take some heater hose and route the draft tube back behind the cab (or further), that would help eleviate fumes and make it even more unlikely that dirt/dust would enter the crankcase.