Basic engine nomenclature
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| − | + | #Piston deck height. This is the dimension from the crown of the piston to the flat deck of the block with the piston at top dead center. Nominally, with a premium 350 piston and a virgin, uncut block, this dimension will be about 0.025". | |
| − | + | #Squish. This is the dimension from the crown of the piston to the underside of the cylinder head with the piston at top dead center and adding in the thickness of the compressed head gasket. Current thinking is that a squish of 0.035" to 0.045" works best. | |
| − | + | #Compression height. This is the dimension from the centerline of the piston's wrist pin to the top of the piston's crown. With a premium piston in a 350 Chevy, this dimension is about 1.560". Lesser quality rebuilder pistons will measure out at around 1.540". This will increase the piston deck height and the squish and make the motor more sensitive to detonation. | |
| − | + | #Stack. This is the combined dimension of the crankshaft radius, rod length and piston compression height. A common stack with a 350 Chevy would be about 9.003". That would be with a crank radius (half the stroke length of 3.480") of 1.74", rod length of 5.703" and piston compression height of 1.560". | |
| − | + | #Block deck height. Nominally, this dimension would be about 9.025" on a virgin small block Chevy cylinder block. So, when using a stack of parts equalling 9.003", this would result in a piston deck height of about 0.022". Combined with a steel shim head gasket thickness of about 0.018", this would result in a squish dimension of about 0.040", just in the middle of the desired range of 0.035" to 0.045" to help prevent detonation with a reasonable (nominally, about 10.0:1) static compression ratio on pump gas. Alternately, a builder might cut the block decks down to the height of the stack and use a more conventional composition gasket that specs out at around 0.040" compressed thickness. If you had a stack of 9.003", cut the block decks down to 9.003" and used a 0.040" gasket, then the piston deck height would be 0.000" and the squish would be 0.040". | |
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