Understanding HP difference b/t 4120 and 4720

[KEG]

I am looking at a JD 4000 series CUT but can't decide between the 4120, 4320, 4520 or 4720. Seems they are identical except for horsepower (HP) - and when I say identical I mean they are exact to every spec except HP. I have heard they get different HP by changing the turbo.

Since the price difference between a 4120 and a 4720 is about $4,500. It would be interesting to see if you could buy the 4120 and do a changeout to increase the HP. For example, buy the 4720 turbo and bolt it on the 4120. The turbo has to cost less than $4,500.

Soooooo ... does anyone know what other changes or differences there may be between the lower HP 4120 and the higher HP 4720?

KEG

 

[jmt1271]

Are they all intercooled? There may be cylinder head differences as well. I am a complete novice with diesels, and just guessing. But surely there are other differences to justify the price. maybe something with the computer as well.

 

[jcmseven]

I am not a JD mechanic by any means, but my understanding is that the engines are essentially the same, with primarily fuel delivery being the difference between them. I am not sure if the turbo is different, but I do not think so. I would defer to another poster on this fact, but I do know that JD will be very hard on anyone if he/she tries to modify one engine to make it more powerful. I have had a 4520, and my neighbor has a 4320. To me, there was very little, if any, perceptible difference in performance between the two. My suspicion is that if you bought a 4120 or 4320, you would get 99% the performance of a 4720 at less cost anyway. Even the 4120, which has the lowest horsepower of the four in the line, has plenty for most any job. The only instance when I think a 4720 would be better would be when doing PTO work which is really pushing the limit of engine power. Those cases are very few. For non-PTO drawbar pull work, the 4120 is every bit the machine as the more expensive one. Having had a 4520, if I were to go back to a large framed green compact, I would probably go 4120 and save the money.

John M

 

[JD3520]

I believe this has come up before and the answer was not only is the turbo different but the computer brain that controls the HP would have to be changed out. Apparently JD saw this coming and took preemptive steps. I'm sure it could be done but your final cost would be more than buying the 4720 to start with.

 

[RRacing]

Actually they have the same turbo in all. And the computer dosen't have any control in it either. The fuel adjustments in the shimming of the injectors and timing of the pump. JD is very secretive about these adjustments.More fuel builds more boost which makes more HP. The 4120 if I remember correctly makes 5-7 LBS of boost were the 4720 is 14-17.

Jim

 

[dunhamg]

So does anyone have access to a service manual for this series of tractor? There must be something in there for the mechanic to set things up correctly if they have to work on one of these tractors.

Grady

 

[ctlguy]

Keep in mind that although is a mechanical setting for fuel delivery on this style of engine that the 4520 and 4720 DO have a ccu engine controller where the 4120 and 4320 do not. This is only on the new 2011 versions, I was to understand that this came about with current govt restrictions based on engine hp levels so large tractor circuitry was added to those last two models. This may not be the case but I would think that this controller has something to do with it but to what regard I do not know. Also keep in mind the govt fine for adjusting fuel control levels beyond where the oem intended is a substantial fine if caught. Typically if you want the real nitty gritty on fuel control systems beyond engine mechanical settings this info only comes from fuel injection shop dealers. Although I do not know what else they can offer for common rail Style of fuel delivery. Not much help I know

 

[creekbend]

There are several differences. The weight, transmission and various other differences can be found on this website: TractorData.com This website contains info on most tractor makes and models. Hope you find what info you need. Good Luck. Please post a reply if this was helful. Have a Happy Day.:tractor:

 

[creekbend]

attn: If you are searching for a manual, perhaps this will help. Go on EBAY, go to SEARCH, type in tractor manuals. Sure wish you luck in your endeavor.:tractor:

 

[AKfish]

This topic has been kicked back and forth since the new line of 4000 series tractors hit the ground!

Please note the date on the OP's inquiry.

If you want to do a bit of "wool gathering" research start here: John Deere - Parts Catalog

Please note the part number differences between the models for the injectors, injector pumps and turbochargers. As well, ctlguy's information regarding the Computer control module's...

I don't think that for $4,500; you'll have much left over with a DIY conversion...

AKfish