Has anyone taken .060" off of a 462 head, or, taken .060" off of any 64 cc chamber head, and then measured the chamber volume? Or is there a generic (probably somewhat inaccurate) formula I can use to find the chamber volume after removing so many thousandths, or a simple way to measure the volume?

 

IIRC, generally you can count on 1cc per 10thou removed when flat milling.

That said, I wouldn't take that much off the head just to increase compression - especially if its a GM casting, as they are often quite thin and will have cracking and warping problems after that much metal is removed.

You would also have to have the intake face of the heads milled and have the intake manifold itself milled to match so that everything lines up and seals properly again. Alot more trouble than its worth.

You'd be better off to do one of 3 things:

- Use a thinner head gasket
- Use pistons with less dish and/or closer to '0-deck'
- Start with heads with smaller chambers. Most of the good 305 heads are between 55-58cc.

 

I already have all the components for a long block, and I will be using .015" thick x 4.100" bore head gasket. The short block is already assembled, and the deck height is about .018". If I can find out beforehand how many cc's I'll be removing (6 cc's?) from the heads, I'll machine them myself. I mentioned '.060"', because I have heard that is usually about the most that can be removed without having to machine the intake, too, but I could probably do that also. I don't see any reason why the intake face on the heads would need to be machined, just the intake would.

I'll probably just assemble everything the way it is and suffer with 10:1 compression until I can afford aftermarket heads, but I would still like to know more accurate numbers for how many cc's are removed while machining 64 cc heads; I would assume the amount would be similar for most 64 cc heads.
For what you said 'generally you can count on 1cc per 10thou removed when flat milling', is that specifically for a 64 cc head?, because I know that can't be accurate from 265 heads all the way to 454 heads.

 

Its a typical amount for a medium sized sbc chamber. I never said it was pinpoint accurate. The only way you'll get a measurement like that is CCing before and after milling. I still wouldn't recommend cutting that much off a factory head - you'll have cracking and warping problems in the future, especially if you overheat it. Same problem GM had with their 'lightweight' head castings in the '70s, because thats one of the locations that lost the most metal with that redesign.

 

Yeah I know what you mean/meant.
I know this has been done before, I thought I'd try and find out what another persons results were.
I guess if the results of machining heads are known to be troublesome, I'll stay from doing that.
Are most aftermarket heads thick enough to be machined that much?

 

Most quality aftermarket heads (AFR, World, Dart, etc) are quite a bit thicker on the deck surface than any factory head will be. My iron World 200cc are about 3/4" thick or so, which is quite a bit more than the factory heads were that they replaced.

If all you want is a smaller chamber, email AFR and see if they will make a Gen 1 SBC head with their smaller 55cc LT1 chambers. Then you don't have to worry about shaving down a perfectly good head.

 

I never knew LT1's had such small chambers.
Maybe I could contact AFR about that. Do you know if they cast the chambers in then machine them, or just machine them from a flat deck?

 

I don't know what their process is, though I'm sure they rough cast it, then machine it out to their specs. Cylinder head castings are always made up of various cores that make up one casting, so they may be able to just use LT1 chamber cores on a regular SBC casting. I don't know for sure though - thats how GM made them in the '50s, maybe its changed.

And 55cc is actually 'big' for an LT1... stock aluminum LT1 heads have 53cc chambers.

 

I found this, but I doubt it is very accurate:
http://www.wallaceracing.com/millcalc.php
Maybe I will contact AFR when it is time for new heads.
I know Pontiac used common castings for different chamber volumes, at least until the early '70's.