JD 790 Power Modifications

[Flywheel]

Just curious - the early 790 was a 30hp tractor - mine is rated at 27hp - what changed adn is there any way to get that back....or more?

I know diesel trucks can be modified through component and software - is there anything to further improve the performance of the Yanmar?

Thanks

[JerryG]

There was a lot of discussion about this, about 3 years ago here on TBN. If I remember right JD actually changed to a different engine. If you do a search, I am sure you will find all you will ever want to know about it.

[RoyJackson]

Originally Posted by Flywheel

Just curious - the early 790 was a 30hp tractor - mine is rated at 27hp - what changed adn is there any way to get that back....or more?

I know diesel trucks can be modified through component and software - is there anything to further improve the performance of the Yanmar?

Thanks

The original 790's (1999) had a 91 cubic inch displacement. This was the 30 HP engine. Around 2002, Deere (Yanmar actually) started using an 81 cubic inch engine. I don't know why, but probably a cost issue (also, the 30 HP engine 790's were too close in power to the 4200 and 4300 tractors). I've also read the original 30 HP ratings (with the 91 cid engine) were somewhat exaggerated...I've no idea if there is any truth to that.
Around 2004-2005, Deere went to another engine, also 81 cid. Again, no idea why, but this may have been a cost or emissions required change.
Another possibility (a guess on my part) is the oil dip stick. On the earlier 81 cid engines, the dip stick is very short and requires the side cover to be removed to check the oil. This is rather inconvenient. Again, that's a guess.

As the frame of the tractor hasn't changed, you could probably put the 91 cid engine into your tractor. As the PTO HP between all three engines is within 1 HP (25 on the early machines to 24 on the 81 cid machines), you really wouldn't notice much difference.

A real diesel guru could probably play with the injection pump for more HP or come up with a turbo set up.

Personally, I think the 790's power is quite adequate (the PTO HP is within 1.5 HP of the 3320's). I do think Deere could upgrade the hydraulics considerably, but that would put a low priced tractor in direct competition with some of their higher priced machines. Also, considering the power, the 790 is a pretty light tractor. The power to weight ratio is pretty good (and keeps the operator out of trouble).

And, of course, the 790 is an old design, stemming from the 1980's. It's probably getting close to the end of it's run.

So, if you want more power, maybe it's time you look at some of the newer models. Even the smaller Deere's have more hydraulic capacity and lifting specs (how much weight do you really need to lift?).

I'm pretty happy with my 790, especially since I got a ballast box to aid in traction (a world of difference). None of my few implements weigh more then the tractor and loader can lift. I'm currently mowing an acre of finished lawn and about 4 acres of field. That's a pretty good fit for my needs.

[JDFANATIC]

Roy,

Nice summary. Weren't you one of the owners that shimmed their hydraulic pumps on this tractor for more capacity? If so, how has that worked out?

[RoyJackson]

Originally Posted by JDFANATIC

Roy,

Nice summary. Weren't you one of the owners that shimmed their hydraulic pumps on this tractor for more capacity? If so, how has that worked out?

Yes, I added shims to the pump.
I cannot give you a quantitative answer, but it does feel stronger when I'm lifting a load.
So far, no adverse effects...

Wish I could be more helpful in this answer.

As I wrote in my first post...if you really want a boost in digging and pushing, get some ballast on that 3PH. I got a really good deal on a Deere ballast box (weighs between 500-600 lbs) which significantly improved my digging capability.

[JDFANATIC]

Originally Posted by RoyJackson

Yes, I added shims to the pump.
I cannot give you a quantitative answer, but it does feel stronger when I'm lifting a load.
So far, no adverse effects...

Wish I could be more helpful in this answer.

As I wrote in my first post...if you really want a boost in digging and pushing, get some ballast on that 3PH. I got a really good deal on a Deere ballast box (weighs between 500-600 lbs) which significantly improved my digging capability.

Ah yes, the easiest thing to add but is often overlooked. Ballast is good. Keeping the shiny side up is even better!

[Flywheel]

Thanks, Roy.

The tractor is a great tractor - i just figured ther might be some tweaks in there - seems like evrything is detuned for safety or marketing nowadays.

I did the shim kit as well - don't notice too much of a difference - yet...

I filled th tires with water as well - couldn't find the beet juice anywhere???

Anayway - out working on a pile of sand this morning with just the box blede on - I see what you mean about ballast - I was spinning a lot.

I think I'll make one with concrete - tough to beat $35 and a little prep time.....or fab a mount on the box blade..


Thanks again -

[ruglad03835]

I find mine to be a stout tractor. I have also owned a 1050 that I bought new in 1986. I find the 790 to handle itself just as well as the bigger tractor. Granted the 1050 could lift more weight. The 300 loader far exceeds the loader on my 1050 in comparison to removing it. As far as ballast goes I have loaded tires, a ballast box, and my backside sitting in the seat for weight over the rear tires. Needless to say there is plenty of weight over the tires. Another nice feature is that it fits in my garage with 2 inches to clear. As I have always said about this tractor: I feel it has the most bang for the buck.