U puller 3rd gear


What size engine would it take to pull a
U Minneapolis moline in 3rd gear in 5500lb class?
425 with good heads and intake ? Thanks .
Wanting to expand past 5mph classes
If want to pull 8 mph will take 800 blocks and heads and at least 7 stroke. Maybe 7.5 and bore blocks to 5.5. Think can find used pistons from a radial plane engine. The guys said theirs were 711. And you need the airplane carb also.
Many variables. Track, sled, chain length, tire size, etc...what may run 3rd at one event may power out in 1st elsewhere. Yes, there can be and often is that much difference between location
Also keep in mind: big cubic inch won't be of benefit if it is not built right. I traded for one 618 ci a few years ago that powered out in low gear first time out. Brought it back home and redid some things would seldom power out in 4th after that. This tractor had the splitter gears in the transmission so 1st gear with 18.4x34 was 6.2 mph. 4th was near 11.
You can put 5.5 pistons and sleeves in short jugs. But not as good because Rods will be shorter. I had a 423 U. M&W Lp pistons and small combustion chamber heads. (Moline heads are terrible valves up in a hole in head. Can't breathe) it would pull in 3rd with 15.5 tires. But not 18.4' X 38. It had 125 hp on pto. My tractor now has 285. A stock RD IHC has 250 so does a 800 moline. To win 8 mph you will need to turn your tires at least 12. And the same tractors will pull against you at 6 mph. In that same gear. I'm just trying to keep you from spending money on a 423 when you need at least 600 cu in. 700 better. And some will be 800. And JD 1000 plus.

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