350 Heavy Duty?

[77GMCSerria]

What exactly makes a 350 a heay duty 350? Is it a 4 bolt main or special heads or intake?

The motor was in a 81 K30 Crew Cab Dually with a auto tranny.

Thanks

[roundedline]

Typically 1 tons had 4 bolts, but I have see several that didn't, so don't count on it.  The 20/30 series trucks had valvtrains designed for low rpm to make pulling power and typically small valves.  For 1981 they had .1 extra compression (8.2 vs 8.3)

The block in itself is nothing special though.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project