Can I get some help understanding what this is? Is it a way to purge the air from the block?

And what methods are best for doing this in swaps?

 

Oh man, do a search and read until your eyes bleed. Opinions run strong on this one.

Yes, just to get the air out. That is why so many members get away with blocking off all 4 vents. Pretty simple matter to crack a vent each time you fill or drain the system and get all the air out.

But it is also pretty cheap insurance to plumb them into some part of the pressurized coolant system, say the radiator, drill and tap the water pump, a T fitting in a hose, or best a separation tank. That way you should never have to worry about forgetting to vent the air.

 

Yes, it is just to get the air out of the cooling system, apparently, these engines need that...
Anyway, the easy way (if you can) is to keep the OEM vents and connecting pipes, and then connect a hose to the rad, below the cap, in the pressurized part of the rad.
In my case I had a nipple soldered under the cap of the factory rad of my '70 Impala, and done!

 

You can block the back two (if they are open) use a crossover tube on the front and use one of these adapters with 1/8 threaded port in-line with your upper radiator hose. These are about $15 or less on ebay or amazon.

 

Wave57 Do u have a build thread?
If not post some pic of the car and the install

 

The reason they have them is because on a 23* head old school smallblock. the highest point of the cooling system with the thermostat closed was the thermostat housing outlet. Air pockets travel up. The thermostat opens and the air pocket goes to the radiator. Thats why alot of guys will drill a tiny hole in the thermostat. To let the air escape.

On an ls. The heads are the highest point and the thermostat is on the inlet. The air pockets will go to the heads. The water pump circulates the coolent, then the thermostat opens and let the cool coolent in. If they are blocked off. Now you are trying to get those air pockets out, in the very corners of the heads, on a theoretical "dead head system". If you cant get that air pocket to move I could see it causing a hot spot in the head. If you can get it to move. You have to hope it gets it all the way cycled through before the thermost closes and gets into the radiator. This is why the line goes to the radiator. Soon as the thermostat opens. you got a direct shot to the radiator.

Some guys say its contributes to the back to cylinders getting hotter. Esp with the #7 cylinder. Other guys will argue till they are blue in the face and say cap them off.

Both ways will work. Im not saying anyone is better than the other. Im just summing up what I learned when doing this. lol

I believe its worth every penny to vent them out. Its something thats cheap and no way can it hurt in anyway. It can only help. Plus with mine being a transplant. My geometry might not be right and the front or rear higher than the other. I did all 4.
I did mine exactly like Casias and the trickflow braided kit. If nothing else. It makes me sleep better at night and thats what matters. lol