The motor my father ran was bone stock internally & nothing really broke, more wore out really bad. His experience with them was he saw cranks break,piston crowns break away bores wear out unusually fast. In our part of the world we also recieved Australian cast engine parts. Castings never seemed to have the same strength/durability as the U.S. cast equivalent. The other problem he had was exhaust seats coming loose under prolonged load. I spoke to another guy who circut raced a 39 Ply coupe with a 250 in the 60's & he had the same problem. To fix the problem it came down to cooling. Make & drill acurately your distribution tube, this helps to keep the valves/seats cooler & stable. Secondly he put a larger pully on the water pump to slow it down. These engine were never designed to rev so high for so long & the coolant at high rpm simply never got the chance to cool down. Remember the fan blade becomes effectively worthless at high rpm so the motor relies on air flow entering the rad. not the fan drawing air in. All of this makes a difference to high rpm reliability. On the subject of bottom ends, nobody really played with them to much because of the crank breakage problems. A guy my father raced against did lie his 250 dodge on it's side to get the center of gravity lower & dry sumped it- didn't make a difference to h/p & he had trouble with reliability so flagged it - 35 yrs ago it was a case of build it/race it/fix it, all home made of course. Just a note - technology has come a long way & the theories & practices have our made our jobs a lot easier than the trial by fire the likes of my father had to contend with. I've learn't a couple of tricks & hope I can pass some on - lets keep it going.
