The 409 engine – talk about WEIRD – these things have no combustion chamber in the heads, and instead have the top deck of the block cut at an angle that is NOT 90-degrees to the crank line to make up for that. They were a bored and stroked old Chevy truck motor, and very inefficient, but the shear size made up for that, and were the beginnings of the American “Big Block” era of the late 60’s.