"And then there'll be some knucklehead that will claim he puts 220 HP thru a D-21 all the time.....yeah, I've heard it all before and also seen the results of that." Know of one that dynoed 180HP...and  the story went like this... Old man farmed a majority of his life with Allis tractors and had done good. the old man's daughter grew up and married a farm boy that worked for his father...  Old man decided that he needed to slow down a little bit and made a deal with S-I-L . So he moved to town and would go out to the farm. S-I-L now bought big green tractors... Old man wanted one of comparable size but not green. LOL so he bought this D-21 with an honest 180HP in it. S-I-L hated it except one day he had to disc down some setaside and didn't want to abuse his green machines and plug up the screens with the bloom and pollination, So he took the D21 to disc with, every pass would overheat and the guy would wipe the grill and pour water in on 70 acres.  Fall came and the old man went around and checked every tractor except the D-21 because it had checked good when he bought it, He didn't know that the S-I-L had added water to it. cracked the block externally so next spring they fiberbonded the crack and it didn't leak so...S-I-L figured his JD's were to good to put on the manure pit agitator/pump. Ran it for three days straight agitating and then pumping. Fall came and the S-I-L drained the radiator... and forgot about the block drains... Well the old man went to move it and found water in oil pan. That was the last it ran. They pushed it to the side and left it. Old man died that winter and in the spring the SIL decided he didn't want or need the 21 anymore and sold it, cuz it was just a piece of junk.  It has sat for 35 years since waiting for an engine to be put in it .