Engine torque

[EternalArianne]

So I had posted a while back about why the older IH cubs had more "umph" than the newer ones yet have less HP, and everyone said it was torque.

On Tractor gearbox website it lists torque for the newer cubs but not the older ones. So I tried running the engine HP and RPM through a torque calculator but the numbers don't seem to add up, even for the newer cubs. For example it lists a 15HP at 3600RPM as having only 21.9ft lbs of torque, but the specs for that particular engine show it as having 25.3ft lbs.

So my question is, what's the best way to calculate engine torque? What kind of torque do the older IH Cub engines have, since they are not listed in the specs? Am I totally missing something here?

[ironman]

I don't know if it will answer your questions but try watching the video at this link....

https://www.quora.com/How-can-I-calc...in-the-formula

[EternalArianne]

The video mention gear ratios as what modifies the torque, so should two engines with equal HP and RPM have the same amount of "baseline" torque?

Does that mean that it's the transmission that gives you the higher torque? Are there any specs for the transmissions showing what these torque modifiers are?

Would it be possible to find a "perfect" pairing between engine and transmission to get the best torque/HP ratio?

[ironman]

Disregarding his talk about transmissions, the chart that he shows depicts that developed torque varies with engine rpm,
therefore Engine "A" will develop peak hp at one rpm and peak torque at another rpm,
while Engine "B" of a different design will develop peak hp and torque at completely different rpms.
So using the example you mentioned above, I would estimate that the peak hp (15) was developed at 3600 rpm while the peak torque (27.3) was developed at 3113 rpm.
Going back to the "umph" of the older cubs, my guess is that the older engine design developed the same amount of torque at lower rpm thus giving it the "feel" of power, much like diesel engine vs. gas engine.

[EternalArianne]

Ah ok that makes more since now, I think I get it. Maybe lol

[ol'George]

Just to muddy the waters, when I was young (and dirt was new) long stroke engines were popular in farm/construction equipment and didn't turn higher rpm's like the later engines in vehicles.
Tractor engines were rated at their max torque at usually less than 1500 rpm's
My 2 cyl JD engines are rated at 1050 max rpm's and the inline 4 cyl. Farmalls were maybe 1200.
in later years, the thinking was shorter stroke and higher rpm's.

[ironman]

I would add that as things progressed in lawn care considerations, the higher hp/rpm became desirable to give the mower decks more cutting rpm for a nicer cut.
Back in the early Cub Cadet days, I don't think grass cutting was thought of as the primary need for one, so more grunt factor was built into them to do the hard work.

[Farmall450]

Originally Posted by ironman

I would add that as things progressed in lawn care considerations, the higher hp/rpm became desirable to give the mower decks more cutting rpm for a nicer cut.
Back in the early Cub Cadet days, I don't think grass cutting was thought of as the primary need for one, so more grunt factor was built into them to do the hard work.

I'd be curious to hear from a Cadet engineer whether blade speed was a driving factor, and what they ballparked. You'd think gearing (pulley size) alone could handle this, and I somewhat suspect that's why they increased PTO size in the 90s. Not to mention belt life and other fringe benefits.

[CADplans]

A local dealer finally admitted to me that he knw all along that Cub Cadets had lower blade tip speed than the red and greene competition.

He could not sell if he admitted that to the customer.

Now that his franchise is gone, he admits knowing.

(I changed the mower pulley on the last Cub cadet I mowed with, then it mowed like a JD!!)

Anyways, IMHO, the high torque comes from the high rotating mass of long stroke engines.
Shorten the stroke, the rotating mass is reduced, less torque.

Short stroke engines are easier to:
build
maintain
sell, because they seem smoother running.
AND, they have WAY fewer repair claims. The engine is never doing as much work.

Oh, yea, way fewer emissions,,

Kiss the long stroke engines goodbye.