Editing Block deck height

First, know that there are two deck heights on a motor. Block deck height is the measurement from the centerline of the main bearing bore to the flat part of the block deck where the heads bolt on. On a small block Chevy, this dimension is usually given as 9.025" from the factory. Not to be confused with piston deck height, which is the measurement from the piston crown to the block deck where the heads bolt on, with the piston at top dead center. This dimension could measure zero or it could be as much as 0.045" if the builder used "rebuilder" pistons that are shorter on the compression height than quality standard pistons, then left the block decks uncut. When combining a 0.045" piston deck height with a 0.040" compressed gasket, the result is a 0.085" squish, which will have little effect in controlling detonation. Squish is recommended at 0.035" to 0.045", so a zero piston deck height with 0.040" gasket puts the squish in the right place (0.040").  

Everyone seems all flustered when you ask them to measure the block deck height on a small block Chevy. The only tools you need are a 12" dial caliper and a pencil and paper. The last 12" caliper I bought was from an ebay auction and I paid 80 bucks for a quality Mitutoyo.

The main bearing bore (less bearings, but with caps snugged down) on a small block Chevy is 2.641". If we divide that by 2, we find that the radius of the main bearing bore is 1.3205". There is room to slide a 12" dial caliper down into the bore of #1, #7, #2 and #8 and snag one end of the caliper jaw on the edge of the main saddle, with the other jaw on the block deck at the edge of the cylinder. Measuring a stock block in this manner might give you a reading of 7.7045". Adding the main bearing bore radius to that figure results in a stock 9.025" block deck height. (7.7045" plus 1.3205" equals 9.025")