How to tell the difference between cast iron and aluminum heads?

Here are some pictures. I FEEL 100% retared on this one thanks for any help you can give.

 

I'm going to say cast iron because of the rust on them.

 

Pull off the valve covers and get the cylinder head casting number. Well, only pulling one of is necessary. That will give you a lot more useful information than just the material type.

Although, they have to be iron. Aluminum does not rust like iron will. Aluminum is not a ferric material, so it will only oxidize. Basically get very dull.

Here's some SBC head casting numbers.

http://www.kendrick-auto.com/chevrol..._number_re.htm

Hope I helped you out.

 

Magnet wont stick to aluminum

 

they would be cast my friend it's pretty hard to confuse, cast look like that and aluminum look like well aluminum .

 

Thanks for the help guys. Not going to pull valve covers off today but will keep that in mind for when I do if ever. Just trying to get the right spark plug and felt like having another opinion.