Over the couple of years I've been on the site I've seen several references to angle milling the slant head. I think I understand the rationale but I'm wondering about a couple of things. First, how much difference does it really make and is it it really worthwhile. Second, what about the head bolts? Do the bolt holes need to be massaged in any way, and what about the bolt head seat? If the head is angle milled then the bolt head will meet the seat at an angle which seems to me would cause problems with uneven torquing and even possible head bolt breakage. Do the head bolt seats need to be remilled too? I'm not really contemplating doing this procedure, rather I'm just trying to learn about it in case I might want to employ it at some later date.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

When angle milling by 0.200" difference across the head, people have also angle milled the bolt bosses on the top of the head. I have done 0.100" across two heads and no boss milling, and zero problems up to 11:1 comp. I have 0.110"/0.210" off one head and 0.080"/0.180" off the other. I mill more on the plug side, as have others I've spoken with. No real world back-back testing I know of, just an idea!

BTW, the chambers in my most milled head are 34cc's, and were 30cc's with different (flathead) valves. They close up some too. Both are '64-'65 heads.

Lou

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Home of Slant6-powered fun machines since 1988

Thanks Lou! Good info, filed away for future reference.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

For the record, I think the angle change on the ports relative to the cylinder is probably not as big an effect as closing up the chamber some.

Angle milling allows you to remove more material since the plug side has less critical features (water jackets) that you would become critically weaker if you did a straight mill of 0.150" to get the same chamber volume as 0.110/0.210". That seems like the main point. Cheap compression w/ stock short block - no disassembly required.

In future, I will likely deck block or get custom pistons to adjust compression, but it's hard to beat head milling for convenience and price.

Lou

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Home of Slant6-powered fun machines since 1988