OK, I've had my theories on this subject. But I wanted to question it and see what others theories are, ect. Here's the example..... OK, the 21hp Kawasaki is just OK on a 48" ZTR running side discharge. The 23hp Kawasaki is strong on a 52" ZTR running side discharge. The 21hp = 38.4 ft lbs of torque The 23hp = 39.8 ft lbs or torque Now... for me, it is hard to believe that 2hp and 1.4 ft lbs of torque accounts for everything in the difference felt. Personally, as I have said before, I think the 48" deck is harder to pull than most think while still generating the same blade tip speed. The ratio between the PTO pulley and the spindle pulleys I believe is to blame. The spindle pulleys have to be smaller on the 48" in order for it to turn the shorter blades at the same tip speed. So the engine-to-deck gearing is higher to create the blade rpm's needed for the tip speed. So it is harder for the engine to turn under load, just like it would be hard to peddle a 10-speed bicycle up hill in a higher gear. Does this make sense? Do you think I am right or wrong? Also, is this also so much of a fact of the matter that you think the 21hp might feel closer to the 23hp if it were running the same 52" deck instead of the 48" deck? Or not? Thanks for your thoughts.