Buying Advice More 2000 series buying advice

[ChuckinNH]

Prior to buying my Kubota, I did test the JD 2320, and 2520 side by side, and threw in the 2305 for a very brief trial too. ( I already had a BX) My findings were substantially the same as jcmseven's. If a dealer that I wanted to do business with had the 2320 in stock set up the way I wanted it, I would be using one today. I was getting ready to start chemotherapy at the time, and had some jobs that I wanted to get done so I went with the Kubota.

 

[MikeCorcoran]

John & Chuck,

Thanks, great evaluations. I'll still take a look at the 2520 he's got on Monday, but
I'll see if he can get the 2320 set up the way I want. The counter-guy looked at stock for me yesterday and there are half dozen within a couple hundred miles. I'm sure the So Cal JD dealers do waaay less volume than most y'all are used to, so their in-store stock is limited.

Mike C.

 

[cbturf]

cbturf,

I appreciate your insight into the 2320 v. 2520 power differences. Unfortunately, the RPM differences are different at the rating point so we do not have a direct comparison. Since these engines typically make more peak torque at lower RPM I suspect if they both shared the same 2600-2650 RPM rating speed, the difference would be much closer. Thusly, if one could tune the 2520 to a 3000 RPM rating speed, I doubt it could make 50 lb. feet of torque. I would expect the 2320 to make around 45-46 lb/feet at the lower engine speed, making it a pretty negligible amount of difference. I was intrigued to find that the slightly more narrow tires of the 2320 seem to grip a little better in gravel or loose dirt than do the fat tires of the 2720 I tried. The 2720, which was ballasted, lost traction more easily up my drive pulling the same size box blade. I suspect to gain full advantage of that machine's power one would have to add substantially more weight. I can say also having tried a 2305 during my testing, the 2320 felt much more powerful and pulled the BB more easily, belying the fact it reportedly has the same engine and tuning (which I doubt--but cannot prove). I also subscribe to the more power club, but unfortunately it might not be as profound as it might seem, and two PTO HP difference for the price difference does not seem to be justified. I think JD has done a fine job of marketing in how they rate these machines--to make it seem as though there is more difference than actually is present. This comes from an owner of two 3720's, a 4520 and a 4310, the 4310 being the only one I felt slack on power. I really wanted to love the 2720, and I did like it, but there was no way I could justify the difference in price for what I saw as a very similar machine.

John M

I think that I may have not explained myself good enough. I will whole heartedly agree that the 2320 will pull a box blade with no problems at all. I was referring to the difference in the two engines and how more torque is better when you are trying to do mowing tasks like he described in the OP.

We all know that torque and horsepower are related to each other. Torque is the rotational force applied to an object and horsepower is the amount of work that an engine will perform. HP=(T*RPM)/5252 or to calculate T at a specific HP and RPM T=(HP*5252)/RPM

If we take the two published PTO HP numbers from the JD website you have
2320 T=(18*5252)/540=175.07 lb/ft of rotational force spinning your rotary cutter.
2520 T=(20.5*5252)/540=199.38 lb/ft of rotational force turning your rotary cutter.

This is a substantial difference and this is why you are only rated to run a 4 foot cutter behind the 2320 and a five foot behind the 2520. Like I said in my OP you will really start to notice the power difference when your cutter blades start to dull and you start ripping the weeds rather than cutting them or you are trying to mow when there is some moisture on the ground and your clippings try to clog up the deck. This is why I ignore horsepower and rely only on torque numbers, that way you can compare apples to apples regardless of RPM.

 

[jcmseven]

Mark,

Please let me make sure I understand you well. It has been many years since my pre-med physics class, but I recall that I did OK in it so I might make this inquisition: if we have our torque/RPM formula for a given RPM: HP*5252/RPM (which I think addresses my concern about rated speed variances). Using this formula it would seem the 2520 produces 26.5 x 5252/2600, or about 53.5 lb/ft. of engine torque at its rated speed. This bears out the JD numbers fairly well for its rating. The 2320 is rated at 3000 RPM, not at 2600. Thusly, 24.1 x 5252/3000 or 42.2 lb/feet of torque at its rated speed, slightly higher than that discussed in the JD literature, but close and correlative with the JD literature HP rating which was used in the formula. If one substitutes 2600 RPM for the 2320, that being 24.1 x 5252/2600 to match the RPM numbers more closely one gets 48.7 lb/ft. of torque at that RPM. Conversely, it would seem that if the 2520 were rated at 3000 RPM, rather than 2600, the formula should show 26.5 x 5252/3000 which would be 46.39 lb feet of torque at that speed. I hope that I am not missing something here, but if this is true, it would first seem to indicate that my previous posting was correct: the 2520 would not make 50 lb. ft. of torque at a 3000 RPM rated speed, The 2320 makes over 47 lb/ft at the same 2600 RPM rating and that the numbers can be manipulated to make the torque difference seem larger than it really is by changing the rated speed as that places a relatively large number in the denominator. If this is indeed true; and again, my simple-minded physics is quite rusty, the actual RPM/RPM torque difference for the engine is 8.9%, rather than 25%; and for rotational torque about 11% for PTO force, given the lower numerators on both, combined with constant PTO RPM for both. Please let me know if I am off target here, but I think my math is right. I also think the RPM rating difference must be considered when reviewing the JD literature as they are prone to rate engines at different speeds and not disclose it. I also have a confession; I calculated this earlier in the post, so if I am wrong here I would have been wrong before, and two wrong's do not make a right. This is not to say that I do not think the 2520 and 2720 are not great machines, but if one looks at the 2000 series lineup it becomes to me apparent that JD has done a nice marketing job. Nowhere in the standard pamphlets that I have did I see what the rated speed is (it is on the website); it merely says "at rated speed." This leads some consumers to think there is an enormous difference between these machines and really there is not, that I can see. I agree that the 2520 would be very marginally better in PTO work, but I bet not much and for non-PTO work I could see no benefit to the 2720 I tried v. the 2320. The loader is DEFINITELY faster in the 2520 and 2720, but even looking at the specs in those shows speed as being the main difference. In my review of the JD literature, the loader specs on each machine were essentially identical save the lifting speed.

John M

 

[skidoo]

You're all making it too complex and concluding HP is irreverent. HP is a measure of Work per unit time. The more HP, the more work per unit time can be done. Or, the same work can be done in less time.


The ratio of your torque on one to the torque on the other is identical to the ratio of HP on one to the HP on the other with rpm being equal.

Ignoring HP doesn't make sense. I would much rather have a torque of 175 lb/ft at 540 rpm (18 HP) than one that makes 500 lb/ft at 1 rpm (0.1 HP)....

 

[AKfish]

You're all making it too complex and concluding HP is irreverent. HP is a measure of Work per unit time. The more HP, the more work per unit time can be done. Or, the same work can be done in less time.


The ratio of your torque on one to the torque on the other is identical to the ratio of HP on one to the HP on the other with rpm being equal.

Ignoring HP doesn't make sense. I would much rather have a torque of 175 lb/ft at 540 rpm (18 HP) than one that makes 500 lb/ft at 1 rpm (0.1 HP)....

I believe that the comparison is not being made too complex - rather the discussion is not complex enough.

The comparison between the different engines is being made upon a linear calculation using a "constant"; and does not provide an accurate calculation based upon a curvelinear method. That's OK; if all you want/need is a general or seat-of-the-pants estimate.

However, anyone who has looked at the torque curve of an engine recognizes that peak torque typically occurs well ahead of peak Hp. Increased rpm does not contribute to increased torque - but quite the reverse - less torque; but more Hp.

AKfish

 

[cbturf]

I will add one last bit to the discussion. Since HP is the amount of work that can be measured over a unit of time and that is our concern why not put a .6L 100 hp motorcycle engine in your tractor, that is absurd because it has no "usable" power like a 1.6L 23 hp deisel does. Furthermore, if horsepower was the main number wy do we not find any 3 Liter 1000 hp at 12000 RPM Indy car engines in the big road trucks. What we have is 13.5L 300 hp 1900 RPM torque monster engines. Torque is king and hp numbers can be manipulated by adding RPM without T. As you can see by looking at the fromula the as RPM increases towards the constant (5252) T and HP converge until they are equal at 5252 RPM, and then after 5252 RPM the HP number will be higher than than torque but the amount of brute force ability decreases. If you just have to compare HP numbers look at PTO hp since RPM is the same and you have your apples to apples comparison on all machines.

I did not mean to hijack the mans question with a HP vs T discussion but he asked my opinion and I gave it and explained why I had my opinion. And I am still of my opinion. I go through the same thing with my mulching machines, a bigger displacement engine at the same HP will produce more T.

It just goes back to the old hotrod saying "Theres no replacement for displacement!"

 

[jcmseven]

I, for one, am not enamoured with HP ratings. I make mention of them in my post mainly for comparative reasons. I, for one, do not mean to have "hijacked" the intent of the post, merely to make a point for anyone looking at a tractor in this size. I do not feel this concern is an esoteric one, nor not-applicable and realize it involves simple math, at best on my part. There ARE many variables which we do not know. We do not know what the respective actual engine torque curves might be, which one makes peak torque at which RPM, etc. We have no idea what driveline losses might be, friction losses, etc. THESE would perhaps be too detailed. I suppose my point when I tested the 2720 and 2320 over the last month of time is that my "seat of the pants" impression was either #1 the 2320 had more torque than advertised, or the the 2720 had less, or a combination of both. When I investigated this a bit more I found the rating speed for the two engines (and also for the 2520 discussed) are different. It appears the number printed by JD is a calculated number, but I assume that they actually ask Yanmar to place these examples of these engines on a dyno to verify their numbers, and potentially generate torque curves which we do not have. To me, this is a very important consideration, because if "torque is king" and we are comparing two similar engines in two similar machines and rating them at different speeds, why would that be done?? The only reason I can think of would be marketing purposes, to make one engine/machine APPEAR to have markedly more torque than another, which based on simple calculation might not be totally true. It is also interesting to me that this is not the case when rating the 3020 series and 4020 series tractors, as they are all rated at the same speed. Why are the 2000's different? I should note, though, that the economy tractors, such as the 3203, 3005, and E series machines, are all rated at different engine speeds, and their torque ratings are very close--but not exact, leading me to feel the predominant difference in their posted torque ratings is the manipulation of the engine RPM, if these are calculated, not actual. To me this VERY important to the purchase of any tractor, because one would hope that by paying additional money, one is getting more than 3-4 lb. ft. difference in torque, plus some additional niceties. It seems to have direct application here as well. I realize this point has been belabored, but I still would like to know am I missing something here on these ratings??

John M

 

[Birdmayon]

JCM, the 2320 and 2520 have different engines. More than likely, the peak torque for the 2320 is produced at 3000 RPMs while the peak torque for the 2520 is produced at 2600 RPMs, which is why they don't list the same RPM level for each in the literature. Maybe that is obvious but I noticed that you keep trying to compare both engines at the SAME RPMs which is not necessarily a valid comparison.

 

[cbturf]

Yes you are missing something in the numbers. The T numbers are not calculated they are measured on a dyno and then you use the formula to calculate HP. I think that I was missing your real question all along! Either an engine makes power or is doesn't, you can not manipulate what it does with a calculator. Now you know why I took my schooling (mechanical engineer) and became a contractor and not a teacher.

Check these engine specs out:

http://yanmar.com/file.asp?F=211D3D719D7B4AEAA9BAFB925DCCE666.pdf&N=3TNV76-CSA.pdf&C=store_items
2320 engine
http://yanmar.com/file.asp?F=9B3BC455794741108361F4E7591DDE0D.pdf&N=3TNV82A-BDSA.pdf&C=store_items
2520 engine
Carol Shelby once said horsepower sells cars (tractors) and torque wins races (mows pastures).