383/388 Chevy stroker
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==Parts stack height== | ==Parts stack height== | ||
| − | When the various parts that make up the reciprocating assembly are selected, these parts have to fit into the SBC deck height dimension of ~9.025". When calculating the stack of parts that make up the reciprocating assembly, use the radius of the stroke, which is the same thing as 1/2 of the stroke, because only 1/2 of the crankshaft stroke swings ''above'' the crankshaft centerline. So for a stock 350 Chevy having a stroke of 3.48", use 1/2 of the stroke (3.480" times .5 = 1.74") to start putting the stack of parts together that will fit into the block. | + | When the various parts that make up the reciprocating assembly are selected, these parts have to fit into the SBC deck height dimension of ~9.025". When calculating the stack of parts that make up the reciprocating assembly, use the radius of the stroke, which is the same thing as 1/2 of the stroke, because only 1/2 of the crankshaft stroke swings ''above'' the crankshaft centerline. So for a stock 350 Chevy having a stroke of 3.48", use 1/2 of the stroke (3.480" times .5 = 1.74") to start putting the stack of parts together that will fit into the block. |
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| + | In a running engine, the oil clearance will create a slightly longer stack- a 0.003" rod bearing oil clearance will add something slightly less than 0.003". In this article, oil clearance will NOT be added into the stack height. If desired the oil clearance may be added; easiest way to do this would be to either add the oil clearance to the rod length, or simpler yet, just add the oil clearance after the stack height is calculated. The added height from the oil clearance would only be an issue if the engine is being built with a marginal amount of quench (<0.035" for steel rods); if built with the "ideal" 0.040" quench, the oil clearance can be basically ignored. | ||
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| + | Another consideration is piston "rock". At TDC as the piston transitions from upward to downward movement, the piston will tip on its wrist pin. This causes one edge of the piston to be a small amount higher than the other edge. The exact amount will vary with how much piston to wall clearance there is; more clearance means more piston rock. Forged pistons generally have a looser piston to wall clearance than cast pistons, but newer design forged pistons have tighter clearances than was used in days gone by. This is another thing that's basically accounted for if a 0.040" quench distance is maintained. Only if less than 0.035" would this possible be an issue. | ||
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| + | The bottom line to all this is it's best to maintain an adequate quench figure of 0.040". There's nothing to be gained by going tighter, and a 0.040" quench distance will avoid unseen problems for the most part. If the quench is less than 0.040", be sure to double check clearances to be sure there is no contact between the piston and head- for obvious reasons. | ||
==Piston compression height and piston deck height== | ==Piston compression height and piston deck height== | ||
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A popular parts combo for a 383/388 stroker is the Scat cast steel crankshaft and Scat I-beam forged Pro Stock rods. The Scat counterweights will clear the pistons using a 5.7" rod and the rods will clear the cam, so no grinding on the rods for cam clearance will be necessary. You may need to do a little grinding on the inside of the block at the pan rail to clear the big end of the rod, but it will be minimal. | A popular parts combo for a 383/388 stroker is the Scat cast steel crankshaft and Scat I-beam forged Pro Stock rods. The Scat counterweights will clear the pistons using a 5.7" rod and the rods will clear the cam, so no grinding on the rods for cam clearance will be necessary. You may need to do a little grinding on the inside of the block at the pan rail to clear the big end of the rod, but it will be minimal. | ||
| − | == | + | ==Quench== |
| − | + | [[File:Squishband.jpg|thumb|350px||]] | |
| + | One way to arrive at a ~0.040" quench distance is to cut the block decks to zero piston deck height and to use a head gasket that compresses to around 0.040". This allows a [[quench]] (or squish, or "squench") measurement of 0.040". Squish is the high speed jetting of fuel air mixture from the dead zone opposite the combustion chamber. When the piston approaches top dead center, the clearance between the crown of the piston and the underside of the cylinder head diminishes to just short of a collision. This squeezes or "squishes" the mixture that is there, across the cylinder toward the spark plug. This high-speed jetting of the mixture not only eliminates any dead spots in the chamber, but also creates turbulence to achieve a more homogeneous mixing of the fuel/air mixture so that there are no lean or rich areas in the chamber. When using steel rods on a street/strip performance engine, having a tight squish of 0.035" minimum to 0.045"-0.050" will allow a high performance street/strip motor to run on pump gas without detonation, providing that all the other important areas are also covered, like the static and dynamic compression ratios. | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
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