I am in the middle of a fairly stock rebuild on my 1970 slant 6 out of my d100. I have been extremely lucky so far and the bottom end of the engine is in excellent shape. I haven't got to the head yet and pulled it apart to see what I'm dealing with but it has been suggested to me in my thread on the overall stock refresh that I port and polish the head as they are notoriously rough out of the factory.
Can anyone give any pointers/tips on how to go about it and how far to go? As stated this is a half ton truck engine not a race engine but anything that will make it breathe better for a bit of elbow grease I am all for!

-Take the head apart and make sure it's good. ( not cracked)
-Grind-out the over-lapping material in the "pocket", just under the valve seats. Grind straight down, do not "under-cut" the seats.
(the black lines in the photo)
-Grind-smooth any other bumps in the port but just a clean-up cut, flush to the port walls.
-Use the manifold gasket to see if there is mis-match between the head's port openings and the manifold ports. ("gasket match") grind away any over-lapping material
DD

Thanks DD!

Is there an area or areas where these heads tend to crack? I will pay close attention to them but I’m pretty sure my head is good; the engine was running pretty well before I started the full restoration on the truck.

Stay away from the walls on each pair of I and E ports for each cylinder. There is a water jacket there that is easy to pop through if you "smooth everything out".

Lou

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Home of Slant6-powered fun machines since 1988

Is this the shared wall between intake and exhaust?

Yes, but not so much an issue on 1975-1987 heads....

Another big area of restriction is the valve guide boss in the runner itself... smoothing and blending is fine for a street
driver... for race a more aggressive approach may be desired before new guides are inserted....

for improving cylinder head port flow,
in the order of general improvement
1) clean up the ports by grinding away casting flash left from the OE foundry operations
2) #1 + install oversized valves
3) #1 + #2 + pay to have a multi angle valve seat ground in
4) #1+ #2 +3 + improve the short side radius
5) all the above + valve bowl work.

this article goes through that progression nicely

http://www.hotrod.com/articles/0610phr- ... d-porting/

as previously mentioned, steps 4 and 5, if you are not familiar with slant six cast wall thickness present the opportunity to ruin the cylinder head.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8