Modern piston design locates the top ring higher for improved performance. a high top ring operates at higher temperatures and requires a larger top ring end gap. To find the proper ring end gap, multiply your bore size by the ring end gap factor listed on the chart (i. e. , Street Normally Aspirated 4. 000" bore x . 0065" gap factor = . 026" total top ring end gap). Your hypereutectic performance piston will expand less than typical cast or forged pistons. Because of this and the wear characteristics of the hypereutectic alloy, you can run tight piston?to?wall clearances. NOTE: Hypereutectic piston engines will require 2?4 degrees less total ignition timing. One key to top performance is to have all cylinders longing for the same timing numbers. Equal air flow, fuel mix, quench, chamber temperature, swirl, and compression at each cylinder work to this end. The following standards are used on all kb hypereutectic non?coated pistons. On 4. 000" to 4. 100", std sizes have . 0005 clearance built into the piston (example 4. 00 bore block, std piston size will be 3. 9995). This allows you to hone std block to attain the . 0015 minimum clearance required in the application Chart. All other oversizes have the minimum clearance built into the piston (example 4. 030" bore block, . 030 piston size will be 4. 0285, . 0015 min clearance).Pit Stop USA offers KB Pistons Performance Hypereutectic Flat Top Pistons - SB Ford 289 - 5.155" Rod Length, .030" Over Bore Size KB115-30 at low everyday prices. Be sure to check out all of our products from KB Performance Pistons including KB Performance Pistons Hypereutectic Pistons - Small Block Ford.