Originally Posted by ryder57
I have the pistons and rods for the 350. Can I use these pistons and which rods do I need. If the 305 heads bump up the compression what about some vortec heads will they be ok? I'm sorry guys I don't know much about this and I appreciate all the help.
Each and every one of us began knowing absolutely nothing about an internal combustion motor, so don't feel bad.
Let me try to help you out with some basics.....
If you're looking at a bare block from the front or rear, you can see the centerline of the main bearing bores where the crankshaft bolts into the block.
From that centerline up to the block deck where the heads bolt on is called the block deck height. On a virgin block that has never been decked or had the main bearing bore altered, that block deck height on a small block Chevy measures ~9.025". When we're choosing parts to fit into the block, we add half the stroke (the radius of the stroke), the connecting rod length (center to center) and the compression height of the piston (distance from the centerline of the wrist pin to the crown of the piston just above the top ring) to find what we call the "stack" of parts to be used in the build.
Now, we know that the stroke of a 327 crankshaft is 3.250". If we divide that figure by 2, we come up with a crankshaft radius of 1.625". If we use a Chevy 5.7" rod and a 1.675" compression height 327 piston along with a 1.625" crank radius and add these 3 values together, we will get a "stack" height of 9.000". Now, if the block deck height is 9.025" and the stack is 9.000", then we know the stack we're planning to use will work and will leave the piston 0.025" down in the bore with the piston at top dead center.
It's the same routine for any motor, just different measurements. For instance, a 350 block would be 9.025" block deck height. The stack for a 350 would be 1.740" crank radius, 5.7 rod length and 1.560" piston compression height. Adding up the 3 stack components, we find a stack height of 9.000", leaving the piston down in the bore by 0.025" with the piston at top dead center. The 0.025" figure is called piston deck height, not to be confused with block deck height.
Same 350, but with a "rebuilder" piston that uses a compression height of 1.540" instead of 1.560" The pistons are made shorter on the compression height to allow the shop to cut the block decks by 0.020" to freshen up the decks if they are a little warped or if you want to equalize all four corners of the block deck with the centerline of the main bearing bore. This would leave us with a block deck height of 9.005" and a stack of 8.980", keeping the 0.025" piston deck height (piston down in the hole by 0.025" with the piston at top dead center.)