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Re: Deve's PCV system (valve)
WarEagle1 #1331865 Wed Oct 30 2019 03:16 AM
Joined: Apr 2002
Posts: 1,699
Fox Offline
A teacher, but always an apprentice.
I appreciate all the help from all the people on this site! Thanks Deve. Thanks Jerry. I will pull my plugs to see if they are oily. I’m not an expert by any means and both of you make a lot of sense to someone who is still a very young apprentice! I remain on the fence on this one! 😃

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1951 GMC 9430 1 ton dually—-Shiny!

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Re: Deve's PCV system (valve)
Fox #1331884 Wed Oct 30 2019 12:40 PM
Joined: Jan 2016
Posts: 567
Shop Shark
Originally Posted by Fox
I appreciate all the help from all the people on this site! Thanks Deve. I remain on the fence on this one! 😃

The PCV upgrade is one of the best things you can do for the engine health.
Another version for the GMC where the draft tube is also the oil fill.
This on is modified by cutting and turning the tube orientation and the road draft is removed.

Attached Files
Last edited by showkey; Wed Oct 30 2019 12:45 PM.
Re: Deve's PCV system (valve)
WarEagle1 #1331900 Wed Oct 30 2019 02:02 PM
Joined: May 2006
Posts: 846
Shop Shark
Here is another GMC configuration I have seen and using on my GMC motor installations.

Attached Files
pcv1.JPG (29.61 KB, 373 downloads)
pcv2.JPG (29.74 KB, 370 downloads)
Re: Deve's PCV system (valve)
WarEagle1 #1331906 Wed Oct 30 2019 02:17 PM
Joined: Feb 2019
Posts: 783
Jack of all Trades, Master of None
Interesting! In this setup it appears that the PCV is drawing air from the valve cover and drawing filtered air thru the crankcase. I assume the canister on the side would be for a filter.


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Re: Deve's PCV system (valve)
Phak1 #1331908 Wed Oct 30 2019 02:39 PM
Joined: May 2006
Posts: 846
Shop Shark
yes. You are correct. A pleated paper filter is used. This set up can be used on a Chevy as well. I usually see these on the military 270's and 302's but have seen them used on 228's etc - for the pre-war trucks and later.

This type of draft tube and filter set up can be found on Ebay. I believe there are a couple on there now.

Locating an elbow or making an elbow for the valve cover should not be too difficult. One of my 261's has a home-made elbow that was tacked to a small metal backing plate, that was then tacked to the underside off the valve cover. A rubber line was then routed to the intake, that was drilled and tapped for a fitting and PCV valve. It works although not the prettiest I have seen.

Seems to make sense.

original filters can be found easy enough with a little patience and perseverance.

Last edited by tom moore; Wed Oct 30 2019 04:46 PM.
Re: Deve's PCV system (valve)
WarEagle1 #1331964 Wed Oct 30 2019 09:03 PM
Joined: Feb 2004
Posts: 20,843
The round track small block V8's we built with extremely loose piston skirt and bearing clearances to prevent the engines from tightening up during extended periods of full throttle operation had massive amounts of blowby, more than any normal type of crankcase ventilation setup could handle. That's just a normal byproduct of race engine building- - - - -"Go fast for a little while- - - -win a few races- - - -blow up into a bunch of pieces of expensive junk!" Repeat as necessary. Run out of money!

The breathers we fabricated were made of two pieces of exhaust pipe about a foot tall, welded to the driver's side valve cover, with vented oil fill caps attached to the top. Quite often, we would zip-tie a couple of folded up shop towels around the breathers for extra filtering. I found that cutting angled slots into the pipes and welding pieces of thin sheet metal into them made the vapors and oil splash negotiate a kind of maze before reaching the top, and kept more of the oil from finding its way all the way to the breathers on top of the pipes. Something similar could be done to a standpipe fabricated to fit the breather hole in a stovebolt block, with the PCV valve at the top of the pipe. A sealed oil filler cap could be added if desired.

The murder victim was drowned in a bathtub full of Rice Krispies and milk.
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Re: Deve's PCV system (valve)
WarEagle1 #1331975 Wed Oct 30 2019 11:05 PM
Joined: Jan 2018
Posts: 187
Shop Shark
I was wondering, would a baffled PCV in the valve cover like most engines I've ever seen make more sense, with a baffled breather on top of the draft tube, or at the other end of the valve cover?
Or, with a filtered breather on the outlet of the draft tube.

Last edited by 4100 Fire Truck; Wed Oct 30 2019 11:20 PM.
Re: Deve's PCV system (valve)
4100 Fire Truck #1332012 Thu Oct 31 2019 02:11 AM
Joined: Mar 2010
Posts: 9,397
Master Gabster
Originally Posted by 4100 Fire Truck
I was wondering, would a baffled PCV in the valve cover like most engines I've ever seen make more sense, with a baffled breather on top of the draft tube, or at the other end of the valve cover?
Or, with a filtered breather on the outlet of the draft tube.

It makes perfect sense.That is why newer engines were fitted with them eventually.
I brought his very point up when Deve proposed his current design years ago.
All you would need to do is use an early draft tube which came with a oil fill cap, put a filtered oil cap on it, and close the lower end of the draft tube. Then put PCV valve on the top of the valve cover.
These old engines are prone to blow by when brand new due to loose tolerances compared to modern engines. This results in contamination of unburned gasoline and water vapor into the crank case. A good portion of these contaminants end up migrating upward and and can be seen wafting out of the vents of the valve cover at idle after a long drive. It also is the white oily gunk seen on the inside of the valve cover.
Having the PCV valve at the top of a ventless valve cover would effectively remove those contaminating fumes.
Having the PCV valve at the draft tube clearly would not. In fact, these fumes will be sucked down through drain holes in the heads and end up in the oil before the draft tube PCV has a chance to sip the fumes out of the crankcase. (PCV systems have a significant amount of restriction in them, so there is not huge amount of air rushing through them. If they did, it would act like a giant vacuum leak.)

resident armchair expert of nothing, but wordy, nonetheless

Last edited by 52Carl; Thu Oct 31 2019 02:13 AM.
Re: Deve's PCV system (valve)
WarEagle1 #1332080 Thu Oct 31 2019 06:01 PM
Joined: Dec 2000
Posts: 3,543
Gas Pumper
Agreed. The amount of suction for the total engine is between 18 and 20 inches of mercury, but for those of us who think more along the lines of pounds per square inch that is between 8.84 psi and 9.82 psi. So, the V-237 pulls out crankcase gases at about 0.98 psi. I would argue that it doesn't matter which direction the suction goes... from the valve cover or from the road draft tube location. Either way, the oil can mix with existing crankcase gases on its journey through the engine since all internal parts are coated with oil. The idea is to create a negative pressure where a slightly positive one exists. With no PCV, you have gases coming out of the valve cover AND the road draft tube which represents positive pressure. By adding a valve and connecting it to the intake, you have slightly (depending on the valve you use) negative pressure which pulls away the gases. (But only if the system is sealed. Valve cover and side cover gaskets aren't leaky, road draft tube port is sealed, and the dipstick has a good seal to the dipstick tube). Since this is all happening every second the engine is running, it's very effective.

I would also remind those of us who were there during the initial discussion years ago that we were all looking for the least invasive way to do this for all vintage 216/235/261 engines. The entire "Keep it Stock!" crowd who many of you are a part of didn't want holes in the vintage valve cover, or in the air cleaner, or in the road draft tube. When Dave and I and a few others engineered the system after lots of feedback from here, it was keeping that solidly in mind. With "Deve's PCV System" (which in actuality was a group effort) the PCV system can be removed, the road draft tube inserted and no harm, no foul.

Since the gases that are present are created on the bottom end as they are on the top due to friction, heat, oil and environmental characteristics, (thus the term crankcase gases) we did the best we could with the design Chevy gave us in the least invasive way. By inserting a freeze plug and grommet at the road draft tube port, we are sealing that hole completely which is important in closing the system for best performance for the valve. With about 1psi of actual pull, there is no chance of oil getting sucked into the valve or any other adverse effects with the added bonus of not affecting vacuum windshield wipers or brake boosters. This system works very well. Is it perfect? I am not sure any PCV system is perfect since you are combatting a problem that was created before the fact. (crankcase gases exist first). I only wish there was an easier way with our vintage GMC (stock) engines to accomplish the same thing. But a little effort and you can get it done anyway! Great conversation!

Research and how to make this system yourself is here:


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Re: Deve's PCV system (valve)
WarEagle1 #1332121 Fri Nov 01 2019 12:22 AM
Joined: Oct 2019
Posts: 45
Wrench Fetcher
Thanks Deve and everybody

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