I talked to the machine shop that built this engine about 18 years ago. I told him I wanted around 350 or more horse. He said he would port the heads, balance the lower end, cam and so on. When he built it before he put a rv cam what ever that was then and bored it 60. I was getting 10-12 miles per gallon which is fine with me. But if I have him do this extra stuff for more power will it kill what little mileage I am getting now? I get 8-10 empty and 4-5 towing now. What do you think