383/388 Chevy stroker
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==Overview== | ==Overview== | ||
A 383 is a 350 block bored +0.030" with a 3.750" crank. A 388 is a 350 block bored +0.060" with a 3.750" crank. The 383/388 SBC stroker has become one of the most popular engines in the history of the small block Chevy. The only engine that surpasses it in volume is the production 305 and 350 SBC. | A 383 is a 350 block bored +0.030" with a 3.750" crank. A 388 is a 350 block bored +0.060" with a 3.750" crank. The 383/388 SBC stroker has become one of the most popular engines in the history of the small block Chevy. The only engine that surpasses it in volume is the production 305 and 350 SBC. | ||
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| + | A 388 can also be achieved by boring a 350 block +0.030" and using a 3.80" crank. | ||
The following article will help the new engine builder to better understand the details involved in building this powerplant. | The following article will help the new engine builder to better understand the details involved in building this powerplant. | ||
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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. | ||
| + | Another example using the 3.80" stroke crank (3.80" x .5 = 1.90") | ||
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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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===Piston rock=== | ===Piston rock=== | ||
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. | 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. | ||
| − | 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. | + | 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. |
==350 SBC piston compression height and piston deck height== | ==350 SBC piston compression height and piston deck height== | ||
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Some builders prefer not to use a 6" rod, the thinking being because the wrist pin intrudes into the oil ring groove- meaning pinned rings or support rails must be used to allow the oil control ring package to do its job- isn't worth the possible advantages from a higher rod/stroke ratio and/or lighter pistons, etc. However, Ross offers a 383 stroker piston with a 1.120" compression height that doesn't require rail supports. | Some builders prefer not to use a 6" rod, the thinking being because the wrist pin intrudes into the oil ring groove- meaning pinned rings or support rails must be used to allow the oil control ring package to do its job- isn't worth the possible advantages from a higher rod/stroke ratio and/or lighter pistons, etc. However, Ross offers a 383 stroker piston with a 1.120" compression height that doesn't require rail supports. | ||
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| + | If that option does not appeal to you, you can use the 3.80" stroke crank as mentioned above, use a 5.7" stroker clearanced rod and a Sealed Power H859CP Piston which has a compression height of 1.425". The stack out will be crank 1/2 stroke 1.9", connecting rod 5.7", Piston 1.425". This will give a stack out of 9.025". This will be dead zero deck height on a standard 350 block. For quench area a thicker head gasket will have to be used such as a FlePro 0.71 MLS. | ||
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<br style="clear:both"/> | <br style="clear:both"/> | ||
| − | Yet another option, although one of the least popular, is to use the stock SBC 400 rod with a 350 SBC piston. The stack of parts looks like: 1.875" + 5.565" + 1.56 = 9.00". The main complaint about using this combo is the rod length. | + | Yet another option, although one of the least popular, is to use the stock SBC 400 rod with a 350 SBC piston. The stack of parts looks like: 1.875" + 5.565" + 1.56 = 9.00". The main complaint about using this combo is the rod length. |
==Clearances== | ==Clearances== | ||
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For clearance, I-beam rods are much easier to use than H-beam rods. | For clearance, I-beam rods are much easier to use than H-beam rods. | ||
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| + | Another option for increased clearance are small base circle camshafts which are designed specifically to give the additional crankshaft counterweight clearance. If using the 3.80" stroke crankshaft this is a must even when aftermarket stroke rods are used. | ||
===Crankshaft and rod to block=== | ===Crankshaft and rod to block=== | ||
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==Aftermarket parts combos== | ==Aftermarket parts combos== | ||
| − | 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. |
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| + | Eagle also makes a great cast steel crankshaft internally balanced for lower power applications such as street engines without power adders. | ||
| + | The Eagle 10352380057I is a great 3.8" stroke crankshaft for up to around 500 HP. It's design exceeds the factory specifications for a stock engine and carries the standard bearing sizes. However, it is not recommended for high RPM use or power adders such as turbos or nitros. | ||
==Quench== | ==Quench== | ||
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==Resources== | ==Resources== | ||
| − | *[http://www.kb-silvolite.com/kb_car/performance.php?action=search&mfg=Chevy&EngSize=383&RodLen=5.7 KB pistons for a 5.7" rod SBC 383 stroker] | + | *<<dead link>>[http://www.kb-silvolite.com/kb_car/performance.php?action=search&mfg=Chevy&EngSize=383&RodLen=5.7 KB pistons for a 5.7" rod SBC 383 stroker] |
| − | *[http://www.kb-silvolite.com/kb_car/performance.php?action=search&mfg=Chevy&EngSize=383&RodLen=6 KB pistons for a 6" rod SBC 383 stroker] | + | *<<dead link>>[http://www.kb-silvolite.com/kb_car/performance.php?action=search&mfg=Chevy&EngSize=383&RodLen=6 KB pistons for a 6" rod SBC 383 stroker] |
*[http://www.gmpartsdirect.com/ GM parts], one of many sources | *[http://www.gmpartsdirect.com/ GM parts], one of many sources | ||
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