Let me give it a shot here, and I am sure I am gonna repeat alot of what has been said. PMSmechanics post at the end of page 1 is spot on.
First: To answer the "Why need more power" question.........alot of tasks with a tractor, traction ISNT the limiting factor. HP is. My 50HP tractor is physically big enough to pull a 15' batwing or bigger. Do I have the HP to run it....NO. Anyone who has bogged down a rotary cutter because they hit a dense patch in too high of a gear....understand what I am talking about. ANYTHING driven off the PTO could stand for some more HP. An average 3000# tractor these days has a ~2500# rear lift capacity and 40HP. So you want to run a tiller? Your limited by nothing other than HP. So, yes, I understand where the OP is coming from in "thinking" that tractors are underpowered.
Second: dynos dont actually measure HP. They measure torque and the computer calculates HP.
Now as to how its calculated, you are correct. Its done the same way. The dyno dont care about max, peak, continuous, etc. Thats a MFG and engineering thing.
You see, those 400hp+ engines in a pickup......thats a peak rating. Can they indeed make 400hp.....yup. Can they do it all day long.....nope.
So a tractor, that is designed for continuous use, needs to be governed. It needs to be "de-tuned" or (underpowered) down to the point where it can work all day long, and still last a lifetime. If tractors were unleashed, with no governing.....people would be blowing them up all the time.
So, while you "can in theory" make a tractor engine make about double its current HP.......It wouldnt be able to sustain it. Thus, they are regulated down to a power level that they CAN sustain all day long, AND still live a full life.
Yes, you are right, the higher the HP the shorter the life. But, if I were to re-flash the PCM in my 2555 and say get 85HP out of it, that would have very little if any impact on engine longevity.
Also, the Mahindra 2565 Shuttle Cab sells for $41,230, the 2555 Shuttle Cab sells for $36,680. They are the exact same tractor except for that 10 HP, which Mahindra makes you pay $4,550 for. Why should we pay over $4500 for a messily 10HP?
This is done across the board, all makes, all sizes of tractors. Its actually cheaper for the MFG to use a LARGE engine, just de-tune it a bit, and meet a lower HP point. Rather than casting a whole new engine block and associated parts. And yes, many times the next bigger HP model, has nothing dont to it other than different programming. Though sometimes there are some other slight differences to cooling system, or drivetrain to handle the extra power, but not always.
You ask why charge $4k+ more for it......simple economics. Supply and demand. They charge more because they can.
Look at johndeere 7x30 series. All have a 414.4 cu in 6-cylinder
7130.........125hp
7230.........135hp
7330.........150hp
7430.........166hp
7530.........180hp
Granted there are some other differences on those models as well. But in your example of the mahindra 2555 and 2655......does it cost mahindra the same amount of money to build each, probably, since its only a difference in computer programming. But if they sold the tractors for the same amount of money.....do you think they would ever sell any of the 2555's? They might as well not even have that model in their lineup. And to have a totally different engine design (rather than just de-tuning an engine) for every HP point they sell at.....would drive to cost of the tractors up across the board. The would have to stock lots more parts, etc.
So instead of looking at it like that extra 10hp costing $4500 being a rip-off. Think of it in terms of getting a really good deal on a 2555 by giving up 10hp.
