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#2---- Clearance Requirements for Hypereutectic Pistons | 1/27/2017 |
Special Clearance Requirements of KB Pistons
(Reprinted from KB-Silvolite website http://www.kb-silvolite.com)
Suggested Piston to Wall Clearance
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 Top Ring End Gap
 The Keith Black pistons 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 .0065 = .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 .060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.
| AUTO APPLICATIONS |
| APPLICATION |
Hypereutectic |
Forging |
| Ring End Gap Factor |
Suggested Piston To Wall Clearance |
Ring End Gap Factor |
Suggested Piston To Wall Clearance |
| Bore To 4.100" |
4.100" & up |
Bore To 4.100" |
4.100" & up |
| Street - Normally Aspirated |
.0065" |
.0015" - .0020" |
.0020" - .0025" |
.0040" |
.0035" - .0045" |
.0045" - .0055" |
| Street - Towing |
.0080" |
.0015" - .0020" |
.0020" - .0025" |
.0045" |
.0040" - .0050" |
.0050" - .0060" |
| Street - Nitrous or Supercharged |
.0080" |
.0020" - .0025" |
.0025" - .0035" |
.0050" |
.0045" - .0055" |
.0055" - .0065" |
| Circle Track - 2 BBL or Restrictor/Gas |
.0070" |
.0015" - .0045" |
.0020" - .0050" |
.0040" |
.0040" - .0050" |
.0055" - .0065" |
| Circle Track - Unrestricted |
.0080" |
.0025" - .0045" |
.0030" - .0045" |
.0040" |
.0045" - .0065" |
.0055" - .0075" |
| Circle Track - Alcohol Injection |
.0060" |
.0025" - .0045" |
.0025" - .0050" |
.0040" |
.0045" - .0065" |
.0055" - .0075" |
| Circle Track - Alcohol Carbureted |
.0080" |
.0030" - .0045" |
.0030" - .0050" |
.0045" |
.0050" - .0070" |
.0060" - .0080" |
| Drag - Gasoline |
.0075" |
.0015" - .0045" |
.0020" - .0045" |
.0040" |
.0050" - .0070" |
.0060" - .0080" |
| Drag - Alcohol |
.0065" |
.0015" - .0045" |
.0020" - .0045" |
.0040" |
.0040" - .0070" |
.0050" - .0080" |
| Drag - Supercharged or Nitrous Gas |
.0095" |
.0020" - .0045" |
.0025" - .0050" |
.0050" |
.0060" - .0090" |
.0070" - .0100" |
| Drag - Supercharged Alcohol |
.0085" |
.0015" - .0045" |
.0025" - .0045" |
.0050" |
.0050" - .0070" |
.0060" - .0080" |
| Drag - Supercharged Fuel |
.0115" |
.0030" - .0050" |
.0035" - .0055" |
.0060" |
.0070" - .0100" |
.0080" - .0110" |
| Marine - Normally Aspirated |
.0080" |
.0030" - .0045" |
.0035" - .0050" |
.0040" |
.0045" - .0060" |
.0055" - .0070" |
| Marine - Supercharged |
.0090" |
.0030" - .0045" |
.0035" - .0050" |
.0045" |
.0055" - .0070" |
.0065" - .0080" |
| Air Cooled Baja |
.0075" |
.0030" - .0045" |
.0035" - .0050" |
.0040" |
.0050" - .0070" |
.0060" - .0080" |
| Propane |
.0065" |
.0015" - .0045" |
.0020" - .0045" |
.0040" |
.0035" - .0070" |
.0045" - .0080" |
| Supercharged Monster Truck / Mudbog |
.0090" |
.0025" - .0045" |
.0030" - .0050" |
.0060" |
.0080" - .0100" |
.0090" - .0110" |
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