THESE ARE BRAND NEW ROSS 8.1 BLOWER PISTONS AND ACKERSLY AND CHILDS RINGS THE BORE IS 4.030,STROKE IS 4100,ROD LENGTH IS 6.200,DECK HEIGHT IS 9.500 WHICH WILL MAKE 418 CUBIC INCH THESE WILL WORK WITH A DART PRO1 205 CC RUNNER HEAD,2.05,1.60 VALVE SIZE.THE RING STACK IS 1/16X1/16X3/16.