1987Z28

Will all GM small block heads Mount up to all GM small blocks. I ask this becase some say for 87 and up GM blocks. Or is this only because of the center bolt pattern? And how do you tell small block heads from big block heads, or does it matter?

markinkc69z

Its because of the center bolts and matching up to the intake. It applies to iron heads. There are 4 basic designs:

55-86 iron - intakes all fit. perimeter VC -'55 unique VC pattern
87-up non vortec vertical center bolts centerbolt VC
Vortec - trapezoidal intake ports. 4 vertical intake bolts centerbolt VC
LT1 iron and aluminum - no water crossover centerbolt VC

david97gsxr

the difference in the 87- is the intake manifold bolt angle, afaik. from what i hear you can drill out the intake manifold bolt holes to fit either style heads.

if you have BBC heads and SBC heads sitting in front of you, the difference is obvious. but the biggest difference if you just have pictures, BBC heads valve springs are staggered. and sbc and bbc heads will not interchange.

1987Z28

so 86 and later sb heads will not mount up to my 87 iroc's TPI, and is this because the bolt holes are different or because the port shapes are different, or both?