How important is engine displacement on same class of tractor?

Hozzie · Nov 19, 2021

I am down to the nuts and bolts of buying a new 70-75HP tractor. Basically down to Kioti 7320, Kubota 7060, and maybe a NH Workmaster 75.

I didn't really notice it before, but they all have quite different engine displacements.

Kioti - 149ci/2700 rpm
Kubota - 203ci/2400rpm
NH - 179ci/2300rpm

Seems to me more displacement at less RPM would in theory work an engine less and over time be more desirable. I like the Kioti overall, but am concerned a bit about such a big difference in displacement between it and the Kubota. Am I overthinking this?

alexpops · Nov 19, 2021

ALL THINGS BEING EQUAL (they never are) more volume ==> more torque. more HP ==> more speed (carries the torque higher into the rpm curve) In theory, you're right, BUT ... the explosion of more volume @ combustion (presumably with more fuel/air) puts more pressure on rings, rods & pistons. The turbo allows you to increase fuel/air pre-compression, but you need higher rpm to spool the turbo, the Kubota should have the higher torque across the rpm curve. What is it being used for? High speed mowing? Probably indifferent. Lower speed ground engagement like skidding logs/plowing? Kubota. JMO

Hozzie · Nov 19, 2021

Mostly being used for 12' batwing and loader work with grapple. Basically an all purpose tractor where I will use a 2 row bottom plow a couple times a year for my garden and run a tiller some for foot plots. I don't "farm" so it will have R4's on it so I don't tear up my yard.

dodge man · Nov 19, 2021

One may have a turbo? I agree all things being equal a larger engine won’t work as hard but I’d still get the tractor you like best.

Hozzie · Nov 19, 2021

They all have turbo's

alexpops · Nov 19, 2021

I'm guessing that for the loader/grapple work the displacement will keep the hydraulics powered up at lower rpm (assuming the pump is big enough in relation to the cylinders to not need high rpm for decent flow). For the plows/tiller displacement is your friend (depends on soil difficulty). I've never run a batwing, but if the cutting can bog you down, more torque and Higher RPM are probably necessary to maintain 540/1000 @ the PTO. Weight/Traction will come into play for the loader/grapple & plow work unless your plowing sand. I'd say, with the possible exception of the batwing & tiller, you could run lower rpms for all the work on the bigger displacement tractor & while it may not save fuel, it's easier on your ears. BUT ... if the emissions require higher RPM to heat up the exhaust you may lose that advantage.

ericm979 · Nov 19, 2021

I think all tractor engines are so understressed and overbuilt that the difference in displacement between models in the same size class is pretty much meaningless when it comes to durability. A 3/4 ton diesel truck makes about 3x the HP per liter and those can go for hundreds of thousands of miles (100,000 miles at 40mph avg is 2500 hrs).

OTOH you might like the sound or feel of one vs the others especially if some are triples and some fours. The lower rpm one might be a little quieter.

FERLING · Nov 19, 2021

Hozzie said:
I am down to the nuts and bolts of buying a new 70-75HP tractor. Basically down to Kioti 7320, Kubota 7060, and maybe a NH Workmaster 75.

I didn't really notice it before, but they all have quite different engine displacements.

Kioti - 149ci/2700 rpm
Kubota - 203ci/2400rpm
NH - 179ci/2300rpm

Seems to me more displacement at less RPM would in theory work an engine less and over time be more desirable. I like the Kioti overall, but am concerned a bit about such a big difference in displacement between it and the Kubota. Am I overthinking this?

Weight of tractor will make the biggest difference between these three. The heavier the tractor the more traction.

Hay Dude · Nov 19, 2021

If all things were equal and quality was equally acceptable, I’d go with more displacement. If the block is heavier, it will dissipate heat better and should run cooler, but there’s other factors in play.
Kubota will give you a much more extensive dealer network and parts should be easier/faster. Plus Kubota is growing rapidly into related equipment sectors.