Straightline Performance 727 Big Bore. Turn your 660 into a mud slinging monster with Straightline's 727 Big Bore. The kit includes new sleeve, piston kit, top end gasket kit, and camshaft. We recommend using a high flow exhaust and intake to achieve the best power with the Big Bore kit. The crank case requires boring to accept the larger sleeve. The compression ratio of this piston is 12:1 and requires the use of 105 octane.Fits: 2004-2007 Rhino 660, 2001-2007 Raptor 660, and 2002-2007 Grizzly 660.