Horsepower on John Deere Compacts

[Tractor King]

I've been involved with John Deere compacts and wonder how Yanmar changed the Horsepower on their engines. I have a JD770 and the engine size and compression is about the same as my JD790, however HP is 6 additional in the 790. How does the companies acheive this. Difference in pumps etc.....????

 

[beenthere]

Have you looked at the engine specs? Are the displacements, stroke, cyl. size, etc. the same?

Seems there are many ways to change the hp.

 

[RoyJackson]

I've been involved with John Deere compacts and wonder how Yanmar changed the Horsepower on their engines. I have a JD770 and the engine size and compression is about the same as my JD790, however HP is 6 additional in the 790. How does the companies acheive this. Difference in pumps etc.....????

790 has a different engine then the 770. Larger capacity and produces more HP/torque.
The first 790s had 30 engine HP advertised. The later models had 27 HP. Over the years, there had been some comments (on TBN as well as other sites) that the original HP rating was somewhat exaggerated.
If your question is just hypothetical...well, you have your answer. If you're considering more HP, it's probably cheaper just to find a used 790.

 

[joes_427_vette]

Makes one wonder when they say this one has 21 hp while another in the same class has 24 hp. I believe this information sometimes is inflated. The pumps are somewhat adjustible and maybe the injector size is increased. It would be interesting to dyno a half dozen and compare the results. Total weight and tire size are a better indicator of performance when rated power is very close.

 

[jcmseven]

Also one must keep in mind that many of the flywheel ratings are "manufacturer's estimates" and that actual operating HP "may be less." John Deere seems especially guilty of doing this, thus comparing PTO HP is likely more accurate in compacts. One can log onto the JD website and check out the "economy" series flywheel v. PTO HP v. the "20" series machines as an example. The flywheel HP is essentially an estimated HP most likely in these cases derived from the formula extrapolate actual measured PTO HP. Though one can dyno test a bare engine, it is much easier to test PTO HP and this is what most companies know will be tested in independent testing. JD has always produced machines that meet or exceed their rated PTO HP when tested by independent third parties but their flywheel numbers may be highly variable. Of course, the other thing to keep in mind is the rated speed, another way that companies manipulate their numbers. All parties do it, and it makes it even more confusing.

John M

 

[JD755]

Thought I would wait for Roy to respond first. He is one of our 790 experts here. As is usually the case with Deere, the errors in their publications make it hard to get details. I have 790 tech manuals from JD dated 2003 and 1999. If you look at bore, stroke, and engine model designations you see the problem. I have attached a single sheet of 790 specs, a page with 770 and 790 specs, and a 790 advertisement from 2001. The single spec page indicates the 790 has a 3TN82A engine. The other one indicates a 3TNE84 although the engine bore does not match. Horsepower numbers also confuse. One shows 30 engine/25 PTO HP. Another shows 27 engine/25 PTO HP.

Something else that does not get mentioned much is that in the early years of the 770 JD advertisements they kept pointing out that while others advertised Gross HP, Deere advertised Net HP. Around 1994 Deere gave in and began advertising both Net and Gross. At that time they said the 770 net was 24 and gross was 25.5. So always compare one to one.

I believe the short answer to your question is the 770 has the 3TN82 while the 790 has the larger 3TN84.

 

[Gary Fowler]

It is not unusual for todays tractor models to use one frame size and engine for 3 or more models. My LS 7010 is identical motor and frame to 7020 and 7030 models with hp ranging from 72-88. More HP can be made by cranking in more fuel and then even more added by putting in a turbocharger and or adding an air intercooler so the intake air is cooler thereby expanding more during combustion thus giving a few more HP. MF does the same with their 1642,1648 and 1652 model. Weights vary slightly due to different sized tires on some and not at all on others (only price varies and even that not by much). This is not a lot different in car engines with same cubic inches varying greatly in HP. Some internal changes may be made to the engines but in my LS they show same model number so it is just the fuel turned up.

 

[glc24]

The pumps are somewhat adjustable and maybe the injector size is increased.

Good point Joe.
How do we know that every (in my case) 2520 injector pump is set at the exact same spec?

Greg

 

[OneMarineE5]

I feel Gary Fowler is correct about pump output!

Consider the current 4020 series. The 4120, 4320, 4520 & 4720 have no discernable differences when viewing their specs yet they all have increased HP and torque ratings as you go up the line. The 4.5L in the 5000 & 6000 series vary their output as well.

Use to be very common with the big-rigs too (not too up with them today). Was fairly common to see an engine put out anywhere from 270 to 425 HP with identical stroke, bore, compression ratio etc.... dial up the pump and the manufacturer had a more expensive engine or an engine for a different vehicle/application.

Keep on:tractor:

 

[JD755]

I think sometimes people forget, or didn't know, that in the past cars usually had several horsepower versions of the same engine you could choose from. This was before every combination of engine/transmission/axle ratio had to go through 50,000 mile emissions approval testing. Because of that added time and expense, each engine today typically only comes in one (maybe two) combination. Years ago, many combinations of carburetors, camshafts, and other things were available just by checking off what you wanted on the dealer order sheet. One size engine might vary from 150 to 400 horsepower. So tractor power variations with one size engine just seem normal to me.