Exhaust Cross Over Ports in 350 Heads, What Size?

I'm wanting to plug the exhaust cross over ports in the heads that heat the intake. Anyone know what size they are? I want to get some freeze plugs and close them off. It has an electric choke and I don't mind it being slightly cold natured. My Stage 1 with Edelbrock heads has not had a choke going back to the mid 80s.

 

Possibly 18 or 19mm. I got mine from napa

 

I think your better off with threaded pipe plugs, I’d have to measure mine as I have to transfer the plugs from my old set of irons.

 

Best block off method I've seen is Storm1's heads, done by Angelucci Performance. They poured molten aluminum in and sculpted it to the port shape, exactly like the others without the crossover.
And I thought my brass press-in solids were nice till I saw those....
Pics of my home made plugs...

 

Those look good Mart!

 

Greg, I think a .750(3/4") freeze plug would pound into the crossover.
My brass deals are .750,
swedge down to .720 to fit deep so I could contour the brass that sticks into the port some. They are 1.625 long.
I did make just basic plugs like this also... they are .760 dia. Kindof crude casting you are pounding these plugs into.

 

I still say that molten aluminum method was absolutely the best! Just like there was never a crossover, and no void left at all.

 

Agreed

 

I ordered a set from Summit to see how it goes. I may take the heads back apart and see how hard it is to pour molten aluminum into them without making a mess.

I assume the preferred method is to use something to block the exhaust valve side of the port and pour the aluminum into the intake side hole? What do you block the exhaust port side with that won't burn up?

 

That's going to be an interesting project. Don't burn yourself! Read up, you could use zinc it seems too.

https://www.classracer.com/classforum/showthread.php?t=60514

You probably can pound the freeze plugs in place to block off alot of cavity that won't have to be filled. I'd probably pour it in from the exh bowl side. Finish the bowl with carbide burr.

 

I'll see what shapes up. I know 600° aluminum can't be wiped off.

 

I pounded in some plugs looked ok used. plugs like mart said they are still in there

 

I put my plugs in today. They fell in at first and I hammered them deeper into the heads. They shouldn't come out, I hope.

 

Yep, drift them in. It's a funky tapered cast hole you're dealing with.

Look good. .750 fit ok then?
That'll seal the aluminum you're going to melt and pour in the bowl side...

 

I think I'm going to just leave it like this if it will run. All I'm trying to do is keep the hot air out from under the intake.

 

Easiest way is usually the best way....

 

It will run fine