horsepower loss vs. elevation

[nedhed]

Hello Everyone! My first post. I have already gotten a lot of great information and insight on Kubotas. Thanks.

I am considering the purchase of a B series. I have 3.6 acres of trees and grass, but no mowing required. The CUT will be used for snow removal, grading and maintanence of 310' of a gently sloping gravel driveway, landscaping, log dragging, etc. The elevation is 8300 ft. I want to know how much extra horsepower I should get to compensate for the elevation. The only info I can find is for LP generators which are derated about 4%/1000ft of elevation above sea level. Is it similar for normally aspirated diesel engines?

 

[v8dave]

I just looked up the derating for altitude of Diesel generators. The recommended derating varied between 3% and 4% per 1,000'. Although, more gensets used 3% that 4%.

Looks like you'll lose 25% of your power at that altitude. I'd check with your local dealer to see what they recommend for continuous use at that altitude. Kubota doesn't appear to make a turbo tractor in the B-series. You might look at some other mfrs and see if they make a turbo CUT tractor. A turbo will make up for a lot of altitude pressure (and resulting power) loss.

 

[bandit67]

I run a Subcompact, 24 hp Case, and my neighbor runs a 22hp BX22, and both machines seem to have plenty of power. Years ago, I ran a 14 hp diesel at sea level, and that had plenty of power, so I figured 24 hp at 5600' would be fine, and it is. I think you'd be perfectly happy with a B7610 (24hp), and certainly anything up to 30hp. These diesel machines are very powerful, even up at altitude.

By the way, I'm sure you're talking to Longmont Farm Supply (they always seem to be asking too much for their machines), so I'd recommend contacting B&G Equipment in Greeley - I found better pricing and the service has been very good - they sell a lot of machines in the Denver Metro area, and especially in Boulder County. PM me if you want any additional info or specifics.

 

[earlw]

I'm at 7,300' here in Peyton, Colorado and had the same concerns as you about the loss of HP at this altitude. From what I have read, 3% loss per 1,000' seems to be the standard I see the most (as someone else already mentioned). But I have seen articles that said the first 1,000' is not included, and others that say it's included, so in your case of 8,300', you could be looking at a loss of 21.9% (7.3*3), or 24.9% (8.3*3).

There is a calculator out there which takes into account other factors like humidity and temp as well. Here is one I found:
Relative Horsepower Calculator . You might want to use WeatherUnderground to get the weather values you'll need to use the calculator.

Oh, just to make sure things are more confusing /forums/images/graemlins/tongue.gif, I called Kubota's division office (not the local dealer), and they said that you use 1% per 1,000' of elevation. I think that is a mistake, I have never seen 1% in my research. They also said to expect more smoke from the engine because of the lack of air density into the engine. Kubota doesn't offer a high-altitude kit or turbo-charger for these compact tractors.

 

[nedhed]

Thanks. It all pretty much confirms my suspicions. Can anyone comment on who manufactures CUTs with turbocharged engines? I'm not expecting there to be any since it adds significant cost to the engine, and it would likely be cheaper just to buy a higher displacement engine. Thanks for the link to the horsepower calculator.

 

[SkyPup]

As far as altitude goes, every single foot is included, including the first thousand simply because the barometric pressure is less as your elevation increases. Whoever thought that the first thousand feet of elevation was equilivant to sea level must have had altitude sickness....

There are some 45-50HP turbocharged tractors, both John Deere and Kubota make turbo models once you get over the mid 40's in horsepower. They all use wastegated turbos so your turbodiesel will perform virtually the same as it would at sea level, ie the 3% loss for each 1,000 foot elevation is negated.

 

[SkyPup]

BTW, the reason the engine power decreases 3% for every 1,000 rise in height is simply because the air pressure decreases by that exact amount and a naturally aspirated diesel is a simple air pump.

We had a barometic reading of 27.9 inches of mercury here at our farm last year (65 feet about sea level) when the eye of Hurricane Jeanne went right over us, making it seem as though we were at about 2,700 feet for a couple of hours..... /forums/images/graemlins/blush.gif

 

[AlbertaKubota]

I am at 4000ft and use a B7800. It works great and I only want more power when I use the tiller. I don't have any problem with other implements. If I follow the calculations I should have 30*(100-4*4) = 30*.84 = 25HP.
In you would use the tractor at 8000ft you only have 20HP. That's a little bit low

 

[JerryG]

<font color="blue">Can anyone comment on who manufactures CUTs with turbocharged engines? </font>
John Deere and Massey Ferguson has small turbocharged tractors. I can't tell you what size the JDs are, but the MF is a 40 hp.

 

[JeffRey30747]

I'm going to go off on a hopefully related tangent here and probably show how little I know, but here it goes.
My understanding has always been that a gasoline engine ignites a metered amount of air/fuel mixture in a confined space to facilitate internal combustion. A diesel on the other hand, injects a metered amount of fuel into an overabundance of air in a similar confined space to acheive the same end result. As a result, it would seem to me that the elevation change would have little to no effect until that overabundance of air was diminished. This probably depends on a number of design factors but with designs where hp increases are acheived by simply tweaking the injector pump settings, I would venture a guess that models on the low hp end of that common design platform would be less affected by altitude change than those on the upper hp end as the upper end models would probably come closer to utililizing the full potential of the air intake design for that model series.
Does this make sense to anyone else?
Jeff