I just put a 1.80 straight cut planetary in my powerglide and a Vasco input shaft w/powerglide splines(i did not want to send the converter back to get turbo splines installed at this time)and the horsepower figures that TCI will quote you on the stock parts is around 650 hp for the 1.76 factory planetary and 500 hp. on the stock input.
I am making an estimated 620 hp and have a 2900 lb. car and when we took the factory input shaft out the converter splines were twisted :shock: ,I made the changes to get the trans to handle around 1000 hp. as we are going to start to spray the car this year and the Vasco input is required for that hp. level,but they tell me that is all the glide splines will hold anything higher than that will require turbo splines.