What to do with the PCV tube?

[JumboFett]

Hey y’all,

I’m building a street performance L20B for my 620 and I’m kinda stumped on what I should do with the PCV oil vent tube coming out of the block. Should I just plug it and make the only crankcase vent the one on the valve cover, or is there something else I can do? 
Thank you 🙏 

[banzai510(hainz)]

that would be the dumbest thing I ever heard off to plug it!!!!!!!!

 

I would cut it where its 90 out and one can run a catch can  or just open vent it as I do.  I will assume you run sidedraft carbs.

 

if run a weber DGV I run it to the bottom of the aircleaner . It helps keep the stink down on a worn motor

[JumboFett]

18 minutes ago, banzai510(hainz) said:

that would be the dumbest thing I ever heard off to plug it!!!!!!!!

 

I would cut it where its 90 out and one can run a catch can  or just open vent it as I do.  I will assume you run sidedraft carbs.

 

if run a weber DGV I run it to the bottom of the aircleaner . It helps keep the stink down on a worn motor

I had a feeling that was the answer just wasn’t sure since the engine has two vents!

Got a suggestion on which catch can I should use? Maybe something I can mount on the firewall?

I’m using a Weber DGV 32/36 that I’m feeding with a cold air intake, and cannon manifold, heat shield wrapped headers, and I’m having the cam reground for a bit more lift and duration. 
 

(edit: now that I think about it there’s probably two vents so one and pull from the other 🤔)

Edited November 23, 2022 by JumboFett

[banzai510(hainz)]

the crankcase  sucks in alot of air above  idle

 what I have notices

But since you going to run a weber DGV set up I would just use the stock type set up. Unfortunatly the stock L20 vent tube is not going to come out in the right spot to hook up to the PVC valve.  I have a L16 set up and there was not much change.

 

the aircleaner vent I routed to the bottom of the weber as it come with a 90 L tube to suck anything from there also. But soem people open vent that also. I route a hose down to the ground so so oil spashes up on the fire wall.   Biggest thing is dont plug up the cramk case vent tube.

 

datzenmike or others can give a better explanation on how to do this

 

heat sheild wrapped headers? somebody told be it makes the header HOTTER and breaks the welds if a cheap header. or holds the moisture in to rust out faster. The stock manifold would have been better but too late now if the exhaust is good. Ceramic coat would be good.

as for the Cam you need now new last pads of the correct size which you dont know what you need and then maybe valve retainers.. Be hones the best bang for the Buck was or is a 38/38 weber dgv if you live in a flat area. if lots of hills then maybe its too much as needs to be dialed in and have more work on motor. Once rolling it goes pretty good but if stuck on a hill it would die out if pushed the pedal down too much to keep the revs up.

Edited November 23, 2022 by banzai510(hainz)

[datzenmike]

4 hours ago, JumboFett said:

Hey y’all,

I’m building a street performance L20B for my 620 and I’m kinda stumped on what I should do with the PCV oil vent tube coming out of the block. Should I just plug it and make the only crankcase vent the one on the valve cover, or is there something else I can do? 
Thank you 🙏 

 

4 hours ago, banzai510(hainz) said:

that would be the dumbest thing I ever heard off to plug it!!!!!!!!

 

 

 

if run a weber DGV I run it to the bottom of the aircleaner . It helps keep the stink down on a worn motor

 

Always keep the PCV valve even if you have to plumb it into the Cannon manifold somewhere. Drill and tap a hole on side near carburetor like the stock one. Valve cover hose fits to the bottom of the Weber air cleaner. There's a Weber part for that.

 

What's with catch cans????? Keep the PCV and you have no need for the catch can. In stock form the PCV valve uses intake vacuum to suck water and gas vapors out of the engine replaced by filtered air from air filter. Excess blow by reverses direction and goes back into the air filter and is sucked into the carburetor and burned. Catch cans you gotta empty that shit out and dispose of. What's the sense of that? You don't need a catch can but somehow after market companies have convinced car owners they can't get by without them. Don't be 'that guy'.

 

 

If you have to pass smog you are already a visual and emissions fail.

 

[Thomas Perkins]

Best way to pass a smog test.Is move to freaking Georgia.

[JumboFett]

6 hours ago, datzenmike said:

 

 

Always keep the PCV valve even if you have to plumb it into the Cannon manifold somewhere. Drill and tap a hole on side near carburetor like the stock one. Valve cover hose fits to the bottom of the Weber air cleaner. There's a Weber part for that.

 

What's with catch cans????? Keep the PCV and you have no need for the catch can. In stock form the PCV valve uses intake vacuum to suck water and gas vapors out of the engine replaced by filtered air from air filter. Excess blow by reverses direction and goes back into the air filter and is sucked into the carburetor and burned. Catch cans you gotta empty that shit out and dispose of. What's the sense of that? You don't need a catch can but somehow after market companies have convinced car owners they can't get by without them. Don't be 'that guy'.

 

 

If you have to pass smog you are already a visual and emissions fail.

 

What do you think about crankcase evacuation through the exhaust using a check valve? They’re a common race engine solution. 🤷‍♂️
 

No smog issue. It’s a ‘74

[datzenmike]

 The PCV valve was introduced in '62. Before that a '50s car would be doing very well to get over 100,000 miles. The PCV draws out the water and gasoline fumes and draws in fresh filtered air. Extends oil changes by about double than without. Oil stays cleaner and less diluted with crap. Keep it functional it's fool proof. Everything is still there, just put together. No need to re-invent the wheel.

 

  

[Ooph!]

2 hours ago, JumboFett said:

What do you think about crankcase evacuation through the exhaust using a check valve? They’re a common race engine solution. 🤷‍♂️
 

No smog issue. It’s a ‘74

 

Some racing classes allow an evacuation system and/or a dry sump engine, its not done for smog reasons its to remove as much air as possible from the crankcase to remove windage and increase power at high RPM's , removing blow by is a side benefit. There may also be Rpm ranges where the vacuum is too low to remove vapor and it will oil mist the area around the vent. Honestly I'd stick with the PCV its simple it works and they don't rob you of power.

Edited November 24, 2022 by Ooph!

[JumboFett]

On 11/23/2022 at 7:28 PM, datzenmike said:

 The PCV valve was introduced in '62. Before that a '50s car would be doing very well to get over 100,000 miles. The PCV draws out the water and gasoline fumes and draws in fresh filtered air. Extends oil changes by about double than without. Oil stays cleaner and less diluted with crap. Keep it functional it's fool proof. Everything is still there, just put together. No need to re-invent the wheel.

 

  

I hear you, and I completely agree that I should maintain a PCV system. I really don’t want to start drilling and tapping holes in the cannon manifold, it’s looking like the most viable solution is to run it through the exhaust with a simple weld-in check valve. Exhaust consistently draws a vacuum of 3-6”Hg, which is more than enough to maintain positive pressure. 

As always, thank you for your advice and insight. 

[datzenmike]

Is there a built in flame arrestor to prevent any chance of all that oil and gas fumes blowing up. Seems rather scary. The PCV does close if you do have a backfire.

 

The cannon should likely have a drilled hole for a brake booster. I think every engine after the 510/521 had boosters.

[JumboFett]

10 hours ago, datzenmike said:

Is there a built in flame arrestor to prevent any chance of all that oil and gas fumes blowing up. Seems rather scary. The PCV does close if you do have a backfire.

There are several stop-gap measures to prevent a backfire from going up into the crankcase: one-way check valve, oil separator, free flowing exhaust, etc. 

My buddy ran this system on his 67 Cougar with a 351W for years and never had any issues. That Windsor had a rumpy cam too; lots of unburnt fuel in the exhaust at idle… no explosions at all. 

[Stoffregen Motorsports]

If you're absolutely set on deleting the PCV system, you can plumb the two vents (valve cover and engine block) into a catch can. You can even plumb the PCV into the catch can to pull a vacuum. Old engines like this will have a certain amount of blow-by, and using the catch can will help keep things clean. If you plumb it properly, the oil that gets in there can drain back into the block.

 

I've built a few systems like this, mostly for high performance applications, but some for the street as well. They have internal baffles to keep the oil from splashing out of the vents. Plumping the PCV into the can works as well as any normal PCV system but doesn't allow much of that blow-by into the intake. The baffles in the can help keep the PCV from sucking up liquid oil.

 

Unfortunately I don't have many pics, but here's one I made 20-25 years ago.

 

 

Edited November 26, 2022 by Stoffregen Motorsports

[Stoffregen Motorsports]

You can also do a sort of cheater PCV system by deleting the PCV valve from the manifold, but then connecting the two hoses together in a tee and then plumbing them to the top or bottom of the air cleaner housing.

 

The reason I call it a cheater system is because having it plumbed to the air cleaner will still pull a tiny vacuum, but only at higher RPMs.

 

Like this. Same engine, but two different air cleaners. You can see the grommet in the top of the Weber air filter, but the hose is disconnected. In the stock modified air cleaner, you can see the grommet in the right side of the air cleaner base.

 

 

 

 

Edited November 26, 2022 by Stoffregen Motorsports

[Stoffregen Motorsports]

There is yet another way to deal with the blow-by. Using an oil-air separator you can plumb it into the two lines. It's basically the same as a catch can, but is not open to atmosphere. Not completely ideal for carbureted street driven vehicles, though I have used them on fuel injected engines.

Edited November 26, 2022 by Stoffregen Motorsports

[JumboFett]

On 11/26/2022 at 10:57 AM, Stoffregen Motorsports said:

There is yet another way to deal with the blow-by. Using an oil-air separator you can plumb it into the two lines. It's basically the same as a catch can, but is not open to atmosphere. Not completely ideal for carbureted street driven vehicles, though I have used them on fuel injected engines.

Thank you 🙏

I definitely don’t want to delete the pcv system and I think I’ve settled on plumbing it into the exhaust to draw vacuum. I can put an air/oil separator in between the block and the exhaust check valve. Any thoughts on that?

[Stoffregen Motorsports]

Running it to the exhaust is an old drag racer trick. I think boats use this style too. I didn't mention it because I don't love it, but it does work. Not like manifold vacuum though. It will work similar to the plumbing to the air cleaner housing - the tiny amount of vacuum will be at higher RPMs. Manifold vacuum will be highest at low RPMs, when the throttle plates are barely open.

 

The main issue with the exhaust style system is the blow-by.  Datsun motors, when run hard, tend to puke oil out of the valve cover, and plumbing it carefully will allow the oil to drain back into the block. Using the oil/air separator will require more than occasional checking to see if the canister has oil in it. They do make those canisters with a clear bottom, so it's easy to see.

 

 

[JumboFett]

9 minutes ago, Stoffregen Motorsports said:

Running it to the exhaust is an old drag racer trick. I think boats use this style too. I didn't mention it because I don't love it, but it does work. Not like manifold vacuum though. It will work similar to the plumbing to the air cleaner housing - the tiny amount of vacuum will be at higher RPMs. Manifold vacuum will be highest at low RPMs, when the throttle plates are barely open.

 

The main issue with the exhaust style system is the blow-by.  Datsun motors, when run hard, tend to puke oil out of the valve cover, and plumbing it carefully will allow the oil to drain back into the block. Using the oil/air separator will require more than occasional checking to see if the canister has oil in it. They do make those canisters with a clear bottom, so it's easy to see.

 

 

As usual all y’all have been incredibly helpful. Thank you