AFTER YOU BOLT ON A ROTATOR GEAR BOX THEY ARE STILL LIGHTER THAN AN O540!!!!!!! I have been playing with them for over a year now we have been getting HP numbers in the 500HP range with our mod's. And almost 600HP with a set of our fully ported heads and custom cam. They also have a very strong bottom end. I have yet too see one get hurt. I don't want to get into specifics until I have at least ten more completed and on the shelf the first 16 flew out the door. Two of them went on air boats. The weakest one yet dyno’ed at 472HP at the Rear wheel, that’s after losing 16% in the drive train. I’m assembling one now that I know will produce over 600HP. It will be thundering around the marsh here shortly. I have been selling a complete version intake to pan with waterpump, flywheel, oil pan, plug wires and complete ignition that makes 450HP for $5,900.