Pistons and rings
From Crankshaft Coalition Wiki
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===Diagram=== | ===Diagram=== | ||
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==Piston design and material== | ==Piston design and material== | ||
Cast pistons are fine for engines that won't see nitrous or boost. Forged pistons are a better choice if the engine will see boost or nitrous due to the added durability. There are those who say using cast pistons and nitrous/boost is acceptable. And it is- providing the tune is spot on and the engine never sees detonation. If it does, the cast pistons will be the first thing to fail, and when they go they usually damage the bore and possibly the cylinder head as well. This is because cast and hypereutectic aluminum alloys are brittle and when they fail they tend to shatter into many pieces, where a forging will generally stay in one piece, with pinched ring lands or depressed crowns, etc. | Cast pistons are fine for engines that won't see nitrous or boost. Forged pistons are a better choice if the engine will see boost or nitrous due to the added durability. There are those who say using cast pistons and nitrous/boost is acceptable. And it is- providing the tune is spot on and the engine never sees detonation. If it does, the cast pistons will be the first thing to fail, and when they go they usually damage the bore and possibly the cylinder head as well. This is because cast and hypereutectic aluminum alloys are brittle and when they fail they tend to shatter into many pieces, where a forging will generally stay in one piece, with pinched ring lands or depressed crowns, etc. | ||
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==KB ring gap and piston to wall clearance instructions== | ==KB ring gap and piston to wall clearance instructions== | ||
| − | {{Note1}}The following info | + | *[https://www.uempistons.com/index.php?main_page=install_instructions United Engine & Machine (includes KB, Silv-O-Lite and Icon) piston installation instructions] |
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| + | {{Note1}}The following info on the KB Icon/Icon FHR (Forged Head Relief) series and various KB hypereutectic pistons used to be on the KB site but has been replaced w/the above link. Refer to manufacturer's instructions to verify these specs as revisions/redesigns may cause them to vary, and for other brands and types of pistons. | ||
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KB pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better and seals the engine for maximum power. When a loose fit engine is desired the rigid skirt design of the KB piston allows the builder a choice without fear of piston damage. See the clearance chart below for minimum and realistic maximum loose fit clearance for KB pistons. | KB pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better and seals the engine for maximum power. When a loose fit engine is desired the rigid skirt design of the KB piston allows the builder a choice without fear of piston damage. See the clearance chart below for minimum and realistic maximum loose fit clearance for KB pistons. | ||
===Special notice on Keith Black piston top ring end gap=== | ===Special notice on Keith Black piston top ring end gap=== | ||
| − | + | The Keith Black piston's unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below. | |
'''Example:''' 4" bore "Street Normally Aspirated" = 4" bore x 0.0065 = 0.026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as 0.060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached. | '''Example:''' 4" bore "Street Normally Aspirated" = 4" bore x 0.0065 = 0.026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as 0.060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached. | ||
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In summary, you can replace cast iron top rings with carbon steel, get all the benefits we’ve talked about in this bulletin, and rest assured we’ve done our homework on the engineering side!<br> | In summary, you can replace cast iron top rings with carbon steel, get all the benefits we’ve talked about in this bulletin, and rest assured we’ve done our homework on the engineering side!<br> | ||
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