HP Rating for D1105 engine

mikeyd · Jan 15, 2007

I own a ZD28 mower with the D1105 engine which Kubota rates at 28 hp @ 3000 rpm. The problem I am having is that they rate the exact same engine at the same rpm at 24.8 hp on other equipment. For example, I have a deposit down on the new RTV1100 coming out in April. It comes with a D1105 engine, same as my ZD28 yet they rate it at 24.8 hp at 3000rpm. Same engine, same rpm .....where did 3 hp go and, more importantly, can I get it back. I know, I haven't even taken delivery of the RTV1100 and already trying to soup it up. Can't ever get enough hp's!!!!!!!!!!!!!! In researching I found other Kubota equipment with the D1105 and some are 24.8 hp and others 28, all at 3000rpm. What gives?

DmansPadge · Jan 15, 2007

I don't really know why they do that... but I think a lot of the time it will be something simply like different fuel injectors that change the HP.

art · Jan 15, 2007

Some engines build a lot of torque and not much horsepower. Some don't build to much of either and probably last a long time. It takes a well machined engine to turn a high RPM as well as using good metal. There are torque differences in most engines by application and I think that is what you will find here.

mikeyd · Jan 15, 2007

Yeah, that's what I am thinking too, maybe just different injectors. My dealer says he can cross reference the injector part numbers once thr RTV1100 comes in. If it is only the injectors that is a real inexpensive way to pick up a 12% gain in power for the RTV.

psdx · Jan 15, 2007

Both the ZD28 mower and RTV1100 actually use engines with the same displacement - 1123cc, however this does not mean they are the same exact engine. Kubota sometimes uses a different head and/or fuel delivery system that will vary the power output.

The B2620 uses the D1105-E2-D21 engine - 26hp @ 2800rpm
The RTV100 uses the D1105-E2-UV engine - 24.8hp @ 3000rpm
The ZD28 uses the D1105-xx-xxx engine - 28hp @ 3000rpm

I could not find the exact model number of the ZD28 engine, but I believe the B2630 & RTV1100 illustrate the point. Perhaps someone can comment on the specific differences to help understand the difficulty associated with modifications for hp increase.

mikeyd · Jan 15, 2007

Thank-you PSDX...no doubt there is a some kind of difference in the motors. My understanding is that the ZD28 uses the D1105-e2-uv so again why the difference? Plus on the other engine you mention, the D1105-ec-d21 when they say 26 hp is that gross intermittent HP because that would be identical to the D1105-e2-uv rating for gross intermittant. The continuous rating for both engines is 24.8, again identical.

I guess what I am trying to figure out is why would two motors with same model number, same displacement and run at same rpm be given different HP ratings by Kubota. I agee that it has to do with fuel delivery or perhaps the head design, the question is what is it and is it simple enough that I can pick up the extra 3hp easily and inexpensively when the rtv1100 gets here. I mean if it is just a matter of buying 3 injectors and installing them on the rtv thats quick easy hp for little money. I can see alot of rtv1100 owners who wouldn't mind a little more power if it is quick and easy and inexpesive.

AB2 · Jan 16, 2007

Here are a few more hp ratings for you. The B2400 engine is the D1105-D10. The B2410 engine is D1105-E-D16. The B7610 engine is also D1105-E-D16. They are all 1123cc and rated at 24 engine gross hp at 2600 rpm. I suspect that all the D1105 engines that have been discussed produce the same power and the differences are only due to ratings at different RPM. For example 24 hp at 2600 rpm, 26 hp at 2800 rpm and 28 hp at 3000 rpm. There may be even more confusion if some ratings are gross continuous or gross intermittent or net continuous or net intermittent etc.
The different ratings may have more to do with marketing than anything else. For example I have a B2400 and the 3pt hitch is rated to lift 1280 lbs. The B2410 replaced the B2400 and the 3pt hitch is rated to lift 1356 lbs. They actually have exactly the same lift capacity. There are 2 sets of holes in the lift arms on both tractors and the B2400 uses one set and the B2410 the other set of holes. Switching which holes are lifted by the rockshaft changes the rating and trades lift capacity for distance. The higher rating may have helped to sell more B2410 tractors even though there is no real change.
You can see hp and torque curves at Kubota Engine America Scroll down to the super 5 series and click on the hp rating.
If you want more power there is a turbo version of the D1105 shown at that site… 6.5 more hp.

mikeyd · Jan 17, 2007

Thanks AB2. However, on both my ZD28 and on the RTV1100 the HP ratings are measured at the exact rpm...3000. This is according to Kubota's own specifications. I have already gone to the Kubota engine site, as well as others, and have yet to see any D1105 engine rated at 28 hp(Peak,gross, intermittant or otherwise), they are always rated at 25hp.

So, the question remains, you have identical engine model numbers, same manufacturer, same displacement, same design, same rpm(3000), one puts out 25hp and the other 28hp. It has got to be more fuel or air , better exhaust etc. which means different injectors, head design or something similar. What I am trying to figure out is what exactly is it so I can make the changes to the RTV1100 engine and pick up the 3 ponies.

Yeah, the turbo is a possibility, especially as Kubota already makes one for this engine. But, I imagine that the cost would be substantial. As I see it, if the only difference in the motors between the 28hp and 25hp D1105 engine is, let's say, the fuel injectors, then that would be a real cheap way to pick up 12% more HP's. Plus, installation would be a breeze.

psdx · Jan 17, 2007

mikeyd said:
As I see it, if the only difference in the motors between the 28hp and 25hp D1105 engine is, let's say, the fuel injectors, then that would be a real cheap way to pick up 12% more HP's. Plus, installation would be a breeze.

If you really want to know, find the part numbers for the injectors on a lower HP and a higher HP D1105 engine. Perhaps the B2630, B7610 and ZD28 would be good samples. The parts manuals can be found here: Kubota Parts Manuals

If someone does the looking - let us know what you find.

mikeyd · Jan 17, 2007

Thanks PSDX......I went to the parts manual and looks like the injectors. Crank, flywheel, cylinder head, injection pump all the same. The injectors show a different part number as between 25hp and 28hp, also some models show different governor part number. Anyways, thank you so much for directing me to this site. Once the rtv1100 comes in I can just compare part numbers to my zd28 and get down to specifics. Thanks again.

Soaring high · Nov 6, 2021

mikeyd said:
Thanks PSDX......I went to the parts manual and looks like the injectors. Crank, flywheel, cylinder head, injection pump all the same. The injectors show a different part number as between 25hp and 28hp, also some models show different governor part number. Anyways, thank you so much for directing me to this site. Once the rtv1100 comes in I can just compare part numbers to my zd28 and get down to specifics. Thanks again.

Hey mikeyd.. been trying to get some info on the x1100c for more ponys have a 2021.. just wondered how you made out with injectors n such please reply thx..

Paystar · Nov 7, 2021

I have two versions of the D1105. One in my new RTV-X1100C, the other in my B2620. Not important to this thread, but wanted to mention something I notice. Both my machines run strong, but I notice my B has almost no exhaust smell, but the RTV exhaust smells like an old big rig. No smoke but it has a diesel odour to the exhaust.
Maybe due to the different tuning between them?

All I know is I like having the matching engines because most of my filters are all the same between the two. That's why I want to get a U27 excavator....it also uses the D1105.

Soaring high · Nov 10, 2021

Paystar said:
I have two versions of the D1105. One in my new RTV-X1100C, the other in my B2620. Not important to this thread, but wanted to mention something I notice. Both my machines run strong, but I notice my B has almost no exhaust smell, but the RTV exhaust smells like an old big rig. No smoke but it has a diesel odour to the exhaust.
Maybe due to the different tuning between them?

All I know is I like having the matching engines because most of my filters are all the same between the two. That's why I want to get a U27 excavator....it also uses the D1105.

Hey psystar.. thx for tuning in.. how is your x1100c power wise I would to gain those 3 ponys we where talking about.. if any info please share thx..

Milo · Nov 10, 2021

There was discussion about Kubota lowering HP ratings back in 2019. What year did you buy your ZD28?

I bought my bx23s last year. The brochure listed the horsepower at 23. I researched the stand alone D902 engine on Kabota's site and it was listed as 21.6. As far as I could tell the engines were identical. I'm guessing Kubota needed to get their info on the engine straightened out.

The same engine can be rated for different outputs, there are 4 ratings they can use also (gross intermittent, net intermittent, gross continuous, net continuous) and there are different ratings based on rpm and application.

Since it appears the PTO hp stayed the same I wouldn't worry about it, although I am curious what brought about the change.

Snobdds · Nov 10, 2021

Always go back to physics. A diesel motor's variables are air and fuel, if the engine architecture is the same.

I know on the massey (Iseki) engines, they use the same engine in the 25 and 23 horsepower versions. The 25 hp spins faster, 3k rpm, to make the rated power, but there is more. The differences are in the fuel shims on the injector pump and governor (2600rpm vs 3000rpm). The 25hp is fed more fuel, which gives it more power. There is some gearing differences in the HST to account for the RPM's but that's it.

It's the fuel changing the power.

Paystar · Nov 10, 2021

Soaring high said:
Hey psystar.. thx for tuning in.. how is your x1100c power wise I would to gain those 3 ponys we where talking about.. if any info please share thx..

I'm only at 620 feet above sea level, but as far as power.....just know they will lose lots of speed, but they never quit pulling. Even when it bogs down, it will still climb idling.

It's hard to tell the steepness in a pic, but my RTV will run 25/26 MPH on the road, verified with my Garmin GPS.
On this hill in my back yard it will run drop to 10 MPH empty, 9 with AC on, or as low as 7 with 2 buckets of pit run gravel from my B2620 in the bed and AC on high. But as soon as it drops if I lift on throttle pedal it picks right back up.

So if you are an ATV trail rider that likes to go fast, you will be disappointed. But me, having done all that and having gone fast racing motorcycles until 2003, I now take the RTV before I ever get on my atv's. I go cruising the trails, I get to see the scenery at lower speeds, it climbs any hill at idle without having to rev and attack the hill, I'm comfortable and clean in the cab, and what burns half a tank of fuel in my atv's, the RTV doesn't even move off full on same loop.

Last weekend I did a test too. I ran up this same hill again with my Boss vee plow on (400 pounds) and a full load of maple hardwood blocks in the bed, and again.....9 MPH up hill. I think it will do ok for me plowing this winter.

But as happy as I am.......if it could top out at 30 MPH, it would be absolutely perfect to me.

Paystar · Nov 10, 2021

I can add also....in this pic where I haul gravel up my bush roads, it will make trips WAY faster than I can make one bucket at a time with my B2620 tractor.

River Valley Landscaping · Dec 23, 2021

I would think the different hp ratings would be mostly for emissions reasons depending on what category of machine it is put in. Similar to the ford powerstrokes that get extremely governed and derated hp and torque when put in a drw dump truck configuration verses a srw or drw pickup truck model with the same engine. I have heard some of the reasoning behind it is because the heavier the truck is, the more likely someone would blow the transmission if all the hp was available. The manufacturers like to play with the torque curves keeping a f650 to a few hundred horsepower and bumping the torque up meanwhile a f350 pickup can be pretty close to double the horsepower in some cases.

Soaring high · Dec 30, 2021

mikeyd said:
Yeah, that's what I am thinking too, maybe just different injectors. My dealer says he can cross reference the injector part numbers once thr RTV1100 comes in. If it is only the injectors that is a real inexpensive way to pick up a 12% gain in power for the RTV.