head identification

How do i know if i have cast iron or aluminum heads? I'm changine the spark plugs and theres different plugs for each.

look at them, the aluminum heads are silver colored and cast iron heads will be black, or more likely rusty

I belive your 90 will have cast iron stock, if that is the car you are asking on

Got magnet?

mmmmmmmm....dont ya love those simple solutions we all dream of?

Unless the head was changed, you have cast iron. AFAIK, in that year, only Vettes have AL heads.