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well.....I have a 5320 and from the dealer it dyno'd 62 PTO horses.....Deere advertises 55. Deere went to a different engine in the 25 series....no wet sleeves for one...but I also think it's maybe a 5 cylinder? Anyway..it's different than the 3 and 4 cylinders the 20 series used. That being said....ALL these new engines have added oil cooling, most are turbo'd and so forth..... lubrication and cooling is pretty much a non issue on modern tractors.....UNLESS you push things to the limit. The first thing you will have problems with is exhaust temperature when you go to cranking up the fuel. All the fuel gets burned and it has got to be exhausted.....you can make the exhaust turn cherry red...and that's not good. I had a very good Deere engine man tell me the 279 cube engine in my 5320 would go way past 100 horsepower....how long it would stay together is another thing. He also told me that Deere has these engines so dialed down nowadays that dialing in 20 extra horsepower was nothing and certainly do-able with zero problems. I was also told that before the engine ever reached being over stressed.....the clutch and drive train generally fails to handle the extra horses. Okay....the whole point is this: It is extremely doubtful that there is any difference at all between any of the tractors you mentioned...except how they were dialed in at the factory. The largest unit may have intercooling in the turbo and the smaller tractors might not.....I don't know and if you don't know....ask the dealer. There is no need in asking the dealer to turn up the fuel..... he wants your money and there being on average $4000 additional every time you go up in size.....that egg sucker isn't going to do you any favors.
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