Block deck height
From Crankshaft Coalition Wiki
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==Deck heights defined== | ==Deck heights defined== | ||
| − | + | 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. The block deck height is 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" "down the hole" if "rebuilder" pistons were used. Rebuilder pistons have a shorter compression height (usually 1.54" compression height or '''''CH''''') than stock or quality replacement pistons (usually 1.56" CH), if the block decks were uncut. | |
An uncut production SBC block deck height is nominally 9.025". When combining a 0.045" piston deck height with a 0.040" compressed gasket, the result is a 0.085" '''[[quench]]''' distance, which will have little effect in controlling detonation. Quench is recommended at no less than 0.035" to 0.045", so a zero piston deck height with 0.040" gasket puts the squish in the right place (0.040"). This isn't the only way a 0.040" quench can be reached, obviously. A better way (and cheaper from the machine shop labor standpoint) is to use a thinner head gasket and keeping the deck as thick as possible. This is easy to do with the 4" nominal bore SBC because of the abundance of '''[[head gasket]]s''' available for that engine. | An uncut production SBC block deck height is nominally 9.025". When combining a 0.045" piston deck height with a 0.040" compressed gasket, the result is a 0.085" '''[[quench]]''' distance, which will have little effect in controlling detonation. Quench is recommended at no less than 0.035" to 0.045", so a zero piston deck height with 0.040" gasket puts the squish in the right place (0.040"). This isn't the only way a 0.040" quench can be reached, obviously. A better way (and cheaper from the machine shop labor standpoint) is to use a thinner head gasket and keeping the deck as thick as possible. This is easy to do with the 4" nominal bore SBC because of the abundance of '''[[head gasket]]s''' available for that engine. | ||
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*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
*[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| − | {{Note1}} Some dynamic compression ratio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure | + | {{Note1}} Some dynamic compression ratio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. <br> |
{{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated: | {{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated: | ||
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