Allante North and I are both doing 425 project engines at this time. With the parts I'm using and my modifications, "Desktop Dyno" projects about 440HP and 480 ft.lbs. of torque. If I'm not mistaken they were originally rated at about 150 net HP. My husband used to get about 14mpg on the highway commuting to work. There's plenty that can be done to them, but for really monster torque, it's hard to beat the 500CI. If you're going to build it up, you've come to the right forum. You should be able to avoid any of the pitfalls we've discovered in our attemps at power.