I'm curious about this one...

On a recent engine rebuild for a '72 Nova that I'm restoring for a customer, we took the engine to a machine shop that absolutely swore by zero-decking the block. I'm curious as to what the general consensus is on zero-decking for performance gains are, or if this guy was simply talking out his *** in order to get more money out of the people having the engine built. I appreciate any input you guys have.

 

Decking can do several things. First by decking you know that the block is level, a used block has a tendency to sink several thousands in the area between the cylinders between exhaust valves. This can cause a blown head gasket here. Also by decking you can bring the piston top up to the block level helping the quench area, which in turn may be worth 5-8 hp and can help reduce detionation. Decking the block will reduce the volumn by 5cc's or so helping raise compression, taking some of the load off of milling the heads

 

If you use flat-top or d-dish pistons and heads that have a flat surface next to the combustion chamber and run a tight clearance (.035-.040") between the piston and head you will cause a lot more turbulence when the piston comes up and compresses the fuel/air mixture. Physics aside, it will cause the mixture to become much more even and atomize the fuel even more, increasing efficiency and lowering the engine's octane requirement.
As a matter of fact, sometimes adding a thicker head gasket to reduce compression will cause the need for HIGHER octane, due to the loss of the squish/quench.