All I can say is if you had a doooog with a 484 or a 509 you had other issues. I've used many in both small blocks and big blocks with bone stock bottm ends and they screamed. The last was a 68 dart with a 508 stock bottom end, stock heads with a good intake carb ign etc. went 12.40's all day long in 90 degree heat and a stock convertor with 3.91's, with street tires and full exhaust. Maybe you need a new tuner?