As Zed Head suggested, blocking off the vent hole in the side of the block will eliminate the entire "positive" part of PCV. The whole concept behind the system is that you positively have crankcase ventilation under all running conditions.

Using two ports combined with the PCV valve, you get flow through ventilation at all times, under all running conditions.

By just using the single port on the valve cover, you lose the benefits of positivity venting your crankcase and you will not have any flow through venting.

@Captain Obvious In my case example, There aren’t any provisions other than one 1/4” bspt vacuum port intended for the brake booster. Running triple carbs presents a problem. Eiji intentionally capped it when he built my engine. I would think if you did tap another hole in the intake you would have an imbalanced vacuum issue on one cylinder. Thoughts?

3 hours ago, Yarb said:

Running triple carbs presents a problem. I would think if you did tap another hole in the intake you would have an imbalanced vacuum issue on one cylinder. Thoughts?

Well my thoughts are that unfortunately you do not really have a perfect solution for your example. If there is no balance tube on the triples, then there's no "symmetric" location to put a PCV valve. As you suggest, without an evenly balanced place to put a PCV, one pair of cylinders will suffer if you were to just stuff it into one of the intakes.

I would, at least, as Duffy suggested, run a catch can on that port on the side of the block. At least that way, you would have two holes a-huffin and a-puffin as the pistons went up and down instead of just one (on the valve cover).

I’m sort of surprised with the number of folks that run triple carbs there isn’t a few kits out there that give more options. In pics I’ve seen both upper and lower locations running to a catch can. Now I need to research whether or not some cans are passive or there are some variety that use vacuum as well.

Edited May 6May 6 by Yarb

https://motionraceworks.com/products/motion-raceworks-top-loader-billet-oil-catch-can-clear-anodized-dual-10-an-port-32-100clr

Here’s an idea that looks plausible. Route both upper and lower ports to the can. Read through the description and present your feedback. Thanks

Advice from Nissan Sport's 'Yellow Books' for race & rally/sporting use:

Close the block breather with a suitably-sized Welch plug, then run the valve cover breather to the 11125-E4675 Oil Catch Can Kit, which is foam-filled and vented to atmosphere. The foam filling catches the suspended oil vapour. Give it a clean out occasionally.

I have seen that sports option catch can on Yahoo Japan auctions now and again.

I run triples and mine is vented to a catch tank. I have seen a k&n round filter put on the end of the standard metal pipe out of the block, but it had been pushed so far in, it didn't vent, may nor maybe not why the engine leaked oil everywhere...

Sometimes you see usually the rocker vent going to a hole made in one of the k&n filters attached to a carb, and thus draws air that way.

My friend has machined a large AN fitting to be a tolerance fit in the side of the block, and then you can add whatever AN fitting to the other end and go where you want.

An option in the v8 world is running the pcv out the block to a pipe on the exhaust manifold so the crank gases are pulled out by the flowing exhaust gases...

In my search for options I found a “AN bung” that could be welded to a freeze plug and drill a hole on the back side. Attach it to the block and go from there. I think I’m going to give that a shot. Wish I had thought of that while it was on the engine stand!!🤦‍♂️🤦‍♂️

https://www.amazon.com/Moroso-22765-Vented-Fitting-Integral/dp/B0FDL8R2M7

Edited May 7May 7 by Yarb

An interesting option, Yarb. But now I have to learn aluminum welding?

The Nissan p/n is 00933-N1401A for the freeze plug or Welch plug if you prefer. $2.50 at your local dealer.

Edit. P/N is incorrect. Picked up the plugs and they are too large. Ended up with the water galley plug instead.

Edited May 9May 9 by Yarb

Both ports have mechanisms to try to separate the oil vapor/droplets from the gas stream before they exit the crankcase/rocker arm areas. The valve cover has a shield and the block port has a wire mesh. Efforts to keep from removing oil from the crankcase.

The racing application might also be designed around the fact that blowby is "dead air". The oxygen has been consumed so recycling it actually reduces power output. It's also probably assumed that the engine will be maintained after every race. A catch-can is a high maintenance item.

For a daily drive odor, cleanliness, and ease of maintenance are probably most important. The blowby gases smell, they're oily, and the catch can has to be monitored and emptied, or the filter and the area around it need regular cleaning.

The standard 240Z carb'ed system runs the blowby hoses in to the clean air area after the filter but before the carbs. So, the carbs get the oily air and the engine does not make maximum power at high blowby levels. High blowby probably contaminates the air filter also. The triple carb setups are generally considered performance setups so power might be more important than the other factors. Don't they make big filter boxes that cover all three carb inlets? They're probably out there but don't look as cool..

Just trying to break it in to parts. And, it's probably more correct to talk about core holes and Welch plugs. That's a lot of words though.

Problem is you need a vacuum source from somewhere. It’s either the intake or the exhaust. If you’re getting 16 plus ounces of oil in that can on a regular basis you have a much bigger problem.