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The Lunati forged, 40cc reverse-dish piston offers the 542ci Indy engine ample combustion chamber size, despite a zero piston deck height and the 78cc chamber volumes of the Indy 440SR heads. This is important. In order to eliminate any chance of detonation with the moderate 9.5:1 compression ratio, the temperature throughout the chamber must be consistent. As a result, combustion occurs predictably across the piston surface. As bore diameters increase, this "squish effect" is harder to control, and when not considered, detonation is a likely result. The series of narrow grooves just below the piston surface are anti-detonation grooves. They also help reduce the chance of detonation as the grooves disperse raw fuel along the cylinder wall through piston travel rather than allowing it to reservoir along the ring and piston top surface. While on the topic of rings, the set is made up of 1/16, 1/16, and a 3/16 standard tension oil ring. The Holley Roadrunner will primarily be a street machine, yet we intend to do a little racing. We made it clear to Ken that we wanted both power and seal without the oil contamination that looser, high-horsepower race engines are known for.