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LarryJ
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2003-03-19          51478

I understand the new BX series tractors have an engine that runs at higher RPMs than the older B series tractors. What is the real difference in these engines? Does this have any effect on the life of the engine? Is this a concern I should have?


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TomG
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2003-03-20          51497

Maybe somebody can comment on specifics of the two engines. My impression is that they are the same basic engines. There may be tuning differences such as cam duration, injector timing, fuel metering, and manifold lengths that affect an engine's power curve.

I don't think there'd be enough difference in the performance of the engines to make much of an issue for most owners. Higher rpm engines may be a bit better for mowing and lower for draft operations, and there may be a bit more wear per hour operation. New oils have reduced wear, and few compact owners would ever wear out their engines even with the old oils. I don't think are enough of differences to make rpm into a major factor in choosing a tractor.
....

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Art White
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2003-03-20          51499

Larry I would not worry about it. I was building diesels that were turning 5000 rpm years ago. With todays tooling there is no reason for concern. The higher RPM broadens the torque curve giving you a wider range of good useable horsepower. ....

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buzst1
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2003-03-20          51513

Hi Larry,
Take a look at the following web site:

http://www.engine.kubota.ne.jp/english/index.html

and look up the current bx and b series engines,the D722,D905,D1005,and d1105. You will notice that when kubota rates the engines for resale they are rated at a maximum of 3600 rpm. What this means to me is that when you are running at the bx rated 3200 rpm you are using almost 90% of the engines rated capacity. If the same engine were running at the more standard 2600 rpm it is running at slightly over 70% capacity. To me that is a big difference that will impact longevity. Acutally, none of this should really make a difference as none of us normally run our machines much over 1800 rpm, but on the bx machines Kubota geared the pto to reach speed (540 rpm)at 3000 thus requiring the bx user to utilize higher rpms.
In the end the bx is still avery good machine and I doubt the orginal owner will have problems. My concern is for later owners and resale value. ....

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slowrev
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2003-03-21          51566

Some of the compact tractor engines reach their maximum torque at a higher engine RPM than the RPM's required for 540 PTO operation. That is poor design and wasted power.
I like the slower tractor engines, more low end torque=usable power.
....

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Art White
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2003-03-21          51569

Slowrev, I don't think any new metal or change of designs would ever change your mind. The International 1066 in the early 70's with the legendary RPM at the time of 2700 and 2800 at the time was unbelieveable to many people when they introduced it. After all, most diesels at that time only revved to about 2000. Those lower revving engines were all based on 50's technology and were made out of softer metals by far than the Melrose engines were. Crankshafts needed turning for nearly every rebuild, egg shaped, not like the newer ones where only if you starve the oil system will you need to turn it. Standard to us was to drop a 4500 rpm govoner spring into the pump and lets go pull! We turned them up more yet, and run like no tommorrow and never grenaded one!!! The wider RPM band allows to build an engine with less overall stress than a high torque, low rpm engine with less flexability of range. ....

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TomG
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2003-03-22          51594

Art: I don't this tractor-pulling side of you has ever come out in your comments before.

I'm thinking about Slowrev's comment about max torque placed above pto rpm and true enough I don't understand the design theory. However, designs are complex and I don't expect to grasp all the complexities.

In my terms I guess there are a couple ways of thinking about it. My first thought is that max torque placed below pto rpm would help support the hp if rpm decreased under excessive loads. Such a design might help a tractor pull through situations where otherwise draft would have to be reduced. However, another way of thinking about it is that if an engine lugs, the first reaction of many operators is to reduce draft. Max torque placed above pto rpm would provide some 'torque-kick' to get the engine back to pro rpm. A lugged engine does have to carry the load plus accelerate itself and the drive train back to speed.

Don't know. The real reasons for one design or the other are probably considerations that escape me. For persons who are unaware of the relationship between torque and HP, the basic idea is that torque = hp/rpm. Another version of the formula is torque x rpm = hp. The actual formula contain a constant.

Regarding the engine stress: I started out thinking that I could see why it might be better if an engine didn't sit banging away at it's max torque rpm all the time during pto work. But then I thought 'well, if power isn't needed fuel the governor reduces fuel delivery to maintain the rpm.' Reduced fuel delivery should also reduce stress. Again, the real reasons for designs probably escape me.
....

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Art White
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2003-03-22          51601

Tom, depending on the injection pump which makes a lot of difference as to the adjustability you can do a lot. To have a low rpm engine with high torque you could exert a higher stress load to the rotating mass than having a larger band of rpm developing the same horsepower. We have seen it in the engines and the parts that need to be rebuilt and when. Case was the industry leader years ago in cubic inches, they were a low rpm engine with a narrow high torque band. They used a softer crank that nearly always needed to be turned. Often found bent rods due to different problems, maybe a leaky head gasket. JD to had softer cranks, not quite as soft as Case but close,IH used a system that was extremely hard, rare to need a turn unless it was scored, nearly impossible to egg like the others and good for high rpm. I can go on and on here and this is about compact tractors not the big ones. ....

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Peters
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2003-03-22          51604

To me the width of the torque band is key and the balance of the engine. If JD and Case had low turning engines then even if the iron in the crank was equivalent then their cranks experienced greater stress due to dyanamic stress caused by the poor balance.
I like an engine that has a low initial torque and a high RPM. The volvo B and F series 4 cylinder engines had a curve the started around 1500 and a max RPM near 6-7K. The engines regularly got 300K miles when NA engines rarely got over 100K. Very fun to drive, but few here would know as they tied it to a slush box rated for the peak HP not the torque.
From what I have seen of the old IH, I think the engine was much the same. Low intial torque and high RPM.
The band on my Cummins is similar 4K max and 1.5 peak.
The a lot of current CUT diesels have little or no torque under 3K. This means that you are running the engine at near max RPM all the time.
I believe that this is done for operating efficiency reason the same as the fact that a lot of engines are limited to automatics for EPA reasons. Longevity is not a primary consideration.
Oh well every thing my change if we go to the small diesel electric hybrids. If you talk to the large equipment operators they have suprising torque for the size. ....

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TomG
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2003-03-23          51660

Art & Peters:

I must have been cooking these ideas over-night. Here I am this morning with some refined ideas--at least refined for me. The engine stress thing may have to do with how active the governor is. The governor on a narrow-band high-torque engine is likely to be more active than on a wide-band engine. An engine at its peak torque rpm that receives frequent full-throttle pulses seems like it would be absorbing more stress than an engine with a less active governor that's not running at it's peak torque.

I seem to be thinking my way to endorsing modern design, but along with Slowrev I do like the feeling of a low rev engine when it gets down to work. ....

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Peters
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2003-03-23          51673

THe fact of life is it that it is easier to achieve an efficient design for a narrow power band than a wide power band.
Companies like Honda etc. have complex systems like variable valve timing, swirl combustion and precombustion chambers to over come some of this in gas engines.
In a tractor you need the power, but not all of it all the time. I have tested tractors that require the engine at the PTO speed to do almost any work, even light bucketing.
Over drives are placed in modern cars for longevity, reducing the speed of the engine.
Balance is required but so is low RPM for longevity. ....

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WillieH
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2003-03-23          51675

WOW, What a Sunday morning breakfast topic!
Switching gears abit...These days, I don't think you could find a very active Governor, regardless of what state your tractor is in.

I think we can all agree, the occasional "throttling" of your particular Governor maybe beneficial for many parties involved...
Oh, TRACTOR governors...har, har
Personally, I would say that the operation of the engine speed, with at least today's units, really are application dependent. Your obviously going to be seeking a higher efficiency if your operating a 3pt generator, as opposed to a pto driven brush. As with many applications, one may be able to get a very satisfactory performance, and engine longevity, from running at 70% or even lower, than running at 90%. Each application potentially requires a different set of parameters.

Willie H. ....

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Art White
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2003-03-23          51683

Willie, active govoners to a farmer are critical and have often made a difference as to farmers uses of tractors. The tractor used on a forage blower when filling a silo needs a quick acting govonor or else he will plug the pipe and be down for 30 minutes unclogging it. The same holds true for many jobs on todays farms not just a generator. I've often listened to customers tell me that a smaller tractor does better in one spot or another than a larger one.It may not be critical for all on this board but someone else might find some very good reasons. ....

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WillieH
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2003-03-23          51695

Art -
I appreciate your comments regarding the silo blowers, etc. As I mentioned, a lot of different applications are seen out there, and, consequently what is a good operating parameter for one application, may not work as well in another. Quite familiar with the farm biz, for over fifty years, we have been selling and repairing electric motors for amongst others, farmers, in our area. Silo blowers were not uncommon to have brought in, not from tractors per say, however the principle remains, slowing down the force feed, whether electric or pto drive, will encumber the efficiency of the process.

Don't read too much into this thread...I'm not disagreeing with what anyone stated, merely pointing out that everyone has a potentially different scenario, hence requiring a slightly altered use of his / her tractor operating parameters.

Willie H. ....

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TomG
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2003-03-24          51734

I was wondering about efficiency as well. Near as I can figure HP can be viewed as a kind of efficiency measure. Other things being equal, HP is torque times rpm, so an engine that has greater torque at some rpm has greater HP and probably greater efficiency as well. Some assumptions here are that the engine displacements and fuel deliveries are the same but this still might be an apples and oranges comparison.

One thing about narrow band engines is that the peak torques are higher than wide-band versions of the same engines. As I recall a style of designing racing gas engines was to narrow band them and shift the peak torque rpm about as high as was feasible. That gives a lot of HP for the displacement. The problem then is to keep the engine operating within a narrow rpm range. I seem to recall that during the '60's Formula Junior drives shifted an average of every 15 or 20 seconds on Grad Prix courses.

Limits to human endurance is probably why automatic TX's came to be used in racing machines, and maybe racing engine design is different now as well. Whatever the design style is today, I'm sure that longevity isn't a goal of racing engine designers either. Efficiency is a goal but only when it translates into HP.
....

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DRankin
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2003-03-24          51746

Maybe we can hear from someone out there who has worn out a BX engine. I have never heard such a tale......

The folks who do ask questions about problems with Kubota engines seem to have tractors that have been out of print for twenty five years and those tractors seem to have had multiple owners, so we cannot track the maintenance history.

Art has alluded to other Kubota engines that have gone many thousands of hours, I don't see any reason to believe a BX engine won't go the same distance. ....

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buzst1
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2003-03-24          51751

This has been a great exchange and I sure learned a lot. I guess now I would really like to know why Kubota with the bx and now Deere in the 2210 have chosen to put the same engines in their "sub-compacts" that they are using in other compacts, gear the pto to opperate at 3000rpm (which is now outside the torque curve) to achieve 540pto and promote them as "higher" HP machines. Could it be that since these tractors are being targeted at the high end consumer (homeowner)market that planned obsolescence has come to the cuts market? ....

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DRankin
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2003-03-24          51758

If you really examine the charts for the D 905 engine you will see the following "net" torque figures:

37.5 foot pounds at 1600 rpm (the chart starts at 1600)

39.5 foot pounds at 2600 rpm (everyones favorite rpm #)

37.5 foot pounds at 3200 rpm (the listed max rpm for BX's)

Now I am not an engineer and I may be missing some nuance here and there, but that looks like a broad, flat torque band.

The rear PTO gets 540 rpm's at 3068 engine rpm, or about 38 to 38.5 foot pounds of torque. Does anyone really believe that dropping 1 foot pound out of nearly 40 is missing the torque curve?

BTW, my JD4100, with a 1.0 liter engine (the BX is .898 liters), gets 39.7 foot pounds at 2650 RPM.

If that sounds familiar see the BX numbers above.
....

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TomG
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2003-03-25          51806

I just thought I'd crank the conversion formula of
Hp = (torque x rpm)/5252 on MarkH's specs because it illustrates the effect of rpm on power very well.

11.4 hp at 1600 rpm & 37.5 ft. lbs.

20.0 hp at 2600 rpm & 39.5 ft. lbs.

23.3 hp at 3260 rpm & 37.5 ft. lbs.

23.9 hp at 3600 rpm & 34.9 ft. lbs.

The formula seems to give the same results as the performance curve on the site Buzz mentioned. I calculated the bottom row at 3600 rpm from torque specs on the site.

What I see on the above chart is a big hp rise in from 1600 to 2600 rpm when the torque also is rising and a moderate rise from 2600 to 3260 when the torque starts falling. The torque drops off so fast after 3260 that the hp is virtually flat beyond 3260 and I imagine it declines after 3600 rpm.

To me the specs also look like a pretty flat torque curve. In terms of using the tractor, it seems that chugging around doing loader work at 1600 rpm seriously under utilizes the engine's potential hp. However, operating at 2000 rpm gains about one ft. lb, and given the torque rise and rpm increase produces almost 15 hp. It seems like its getting into its power range around 2000 rpm. At 2600 rpm there's still considerable room for more power by using lower gearing to increase rpm while maintaining ground speed. That might work if a load is lugging the engine up to about 3260 rpm and then there's no further power increase.

So, I get a 'working power range' of something like 1200 rpm, which isn't huge but isn't bad either. I hope these numbers helps illustrate something of this torque/hp buz. I don't think anybody here has ever said that BX, or any other CUT diesel, lacks longevity. I was just thinking through Art and Peters comments about narrow band engines placing more stress on an engine.
....

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buzst1
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2003-03-25          51823

Hi guys,
I am not questioning the power or quality of the sub compact tractors and apologize for continuing to dwell on this topic. But, I really do not understand either Kubota or Deere’s rational for up rating their subcompacts. As I see it:
1.)Both the bx and 2210 use the exact same engines that have been very successfully used at lower rated rpm in other tractors (3TNE74 in the 4110 and d905 in the b1700). They did not design a new engine intended to operate at a higher rpm.
2.)The smaller wheels/tires used on the subcompacts prevent full transfer of any additional HP to the ground.
3.)The 3pt on the subcompacts is not large enough to accept attachments that can utilize the higher PTO HP.
4.)Continued use at higher RPM will increase the opportunity for failure.
5.)Continued use at higher RPM will shorten overall lifespan.

So, I can only see two reasons the manufactures are promoting the sub compacts in this fashion:
1.) By decreasing mean time between failures they are getting the customer back to the dealership more often, as well as reducing the competition for new business from their older machines that are being sold on the used market.
2.) the manufactures believe the dealer sales force is not able to effectively sell against the higher end garden tractors in the 16-25 hp class (simplicity, cub, etc)

This all may sound somewhat cynical but why else are they being rated this way?
....

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Art White
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2003-03-25          51825

That is a way to look at it. But I look at it differently than you maybe, a little different perspective as I get to listen to what people would like buy. The reason of the RPMs and the torque curve tends to fit the general applications that these tractors are used for. The extra rpms for you is not extra for us, they have done it for years. The fact that if you have 5 acres or ten and want a compact but can't justify the expense, you can often afford a BX Kubota when comparing the initial price difference with a full sized garden tractor equipped with Brand dedicated equipment which only fits "that make and model" tractor. Often it is tough to justify purchasing a attachment because you will wear out your garden tractor or choose to replace every so often and can't afford it. Buy buying a BX it gives you the flexibility to expand your attachments and flexability. I've only had two traded in, both were BX2200's for BX22's with the backhoe attachment. I certainly thought that both were good fits as well as the customers as many more perspective customers come in telling of these owners satisfaction. To lead the industry with the forsight to produce equipment that is unavailable thru your competition and to fill this void like the Kubota BX is what business is all about! ....

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buzst1
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2003-03-25          51828

Hi Art,
Thanks for the reply. when you say

"The reason of the RPMs and the torque curve tends to fit the general applications that these tractors are used for. The extra rpms for you is not extra for us, they have done it for years"

You are touching on the issue I am having a hard time understanding. What are the applications that your customers are doing better by utilizing the additional rpm of the bx than they would have done with the B1700 at 2600 rpm? I fully understand the general benefits of the bx just not specifically what is gained by requiring additional engine rpm to obtain 540 pto rpm over what can be done with the B1700? ....

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Art White
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2003-03-25          51839

The ground speed would be a little slow if you didn't have the extra RPM. With a flat curve on torque it allows you to start a little higher rpm and still run pto equipment well. Not all people run the equipment at the required rpm for a big torque curve. They are used to gas engines which often turn higher rpm and tend to drive the compacts the same way, not like a tractor as they have never been on one much less operate one. We do have engines with huge power bulges on torque. To look at some of the other lower rpm Kubota's you will find some of those engines do have the bigger bulge much the same as some of our Case-IH engines. ....

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buzst1
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2003-03-26          51902

Hi Art,
Thanks I think I got it. Are you saying that the smaller tire size of the sub compacts require higher rpm to achieve "normal" ground speeds within the confines of the torque curve?
....

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slowrev
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2003-03-26          51914

I thought the groundspeed/PTO speed was a function of engineering the gearing of the treansmission to match the engine/tire size together as a well balanced package. That was what I was referring to in my previous post suggesting poor engineering. ....

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DRankin
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2003-03-26          51915

Slowrev, if I am understanding your point correctly, then you would be saying that the BX is "set up" correctly.

The 540 pto speed is achieved at 3100 RPM, at the top of the operating range. And of course the HST allows you to choose any ground speed between 0 and 8 mph while running at that RPM. ....

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slowrev
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2003-03-26          51924

Mark,
Yes, It would appear so for the high reving engine. Just a personal prefrence though... I like lower reving high torque engines.

Torque is where it is at, no RPM.

....

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Art White
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2003-03-27          51968

Hey, just a thought slowrev, maybe you are not one of the people that the BX was built for. I know I've never seen the perfect piece of machinery for anyone! I've seen a lot of machinery that is good enough to get the job done and it is the best that is available. But I've never seen that perfect machine! No offense, just a fact, thats why Kubota has other models of tractors. There are many engines out there in tractors with a larger power bulge and lower rpm that are very suited to you and the way you wish to use your equipment. There is no reason otherwise not to spin a diesel engine to the same speeds as a gas engine. You can have problems with such a large mass spinning it fast if it is not balanced or built with good material or design. But getting away from the quality they can be reliable and durable. ....

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TomG
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2003-03-27          51973

Some years back I heard a popping that sounded like some sort of peculiar shot gun practice or maybe one of those acetylene gadgets that are supposed to keep birds away from crops (and don't work very well I hear). I was visiting on the central California coast.

Somebody told me it was a gas engine used to drive pumps used in oil fields. From the popping, I'd guess the engine was running at less than 60 rpm. More guessing is that they have big torque and low HP for their displacement and probably last indefinitely. I imagine the engines drive huge flywheels that would store energy from infrequent torque 'pops' to keep very long stroke pumps going.

I have to assume that this would be the best design possible for the particular application and it would work only for constant loads. Such an engine wouldn't accelerate very well. The extremes designs can take for specific narrow applications always is amazing to amateurs like myself.
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DRankin
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2003-03-27          51981

I suppose that if longevity was a big problem in high revving diesels then we would be hearing complaints from Mercedes, Audi and VW owners.
Those Cummins engines in Dodge trucks must turn more than 3000 rpm? ....

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slowrev
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2003-03-27          51983

Art,
No offense taken, Hopefully no one has taken offense at my posts, if so I apoligize. No the BX22 is not for me, I like something larger. Just don't care for high reving tractor engines.

"There is no reason otherwise not to spin a diesel engine to the same speeds as a gas engine"

Is there a RPM limit to diesels because of the burn rate of diesel fuel in the combustion chamber ? No sure, but I would think it would burn slower than gasoline. ?? Just a thought, way out of my field there.

Ben

....

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buzst1
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2003-03-27          51985

Hi Guys,
My questions were never intended to compare high vs low reving engines.
All I was trying to understand was why Kubota and Deere are using the exact same engine in their subcompacts as in the compacts, reving it up and rating it for higher HP than when used in the compact. I don't think there can be any doubt that if you take two engines that are exactly the same, run one for 3000 hours at 3200 rpm, run the other for 3000 hours at 2600 rpm, the engine that ran at 2600 will have had fewer problems and be in better shape at the end of the 3000 hours than the other. Based on this asumption it didn't make sense to me that the manufactures would do it without design or marketing reason and I couldn't come up with any design reasons. Art's point about higher rpms being necessary to obtain reasonable ground speed with the smaller tires seems to be a valid reason the manufactures would make this sacrifice in longevity.
Thanks all... ....

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slowrev
Join Date: Jul 2003
Posts: 231 Winchester , KY
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2003-03-27          51989

Buzst1,
Sorry we got off on the side road on this one, it is a recurring sore point with many folks on one side or the other.

I think you hit the nail on the head. Same engine + more RPM = more HP = less cost to the manufacturer than building a larger displacement/stroke engine. But not necessarially better for the consumer, could be ok, depends on the gearing.

I do agree though the more revolutions the engine turns = more wear = less life.



....

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Art White
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2003-03-27          51993

There is far more than meets the eye when talking about horsepower and torque and engine life. I have played up to 5000rpm with the standard cam and only mild engine work and pump,turbo and injector work. Just like cars, have you seen the new honda's with a 9000 red line from the factory? It's the quality of the metal and how it's put together. When the Kubota's are out there at 2700rpm and last over 10,000 hours when properly taken care of than what's a couple of hundred more rpm. Cuts the life to 9,000 hours? Many manufacturers are satisfied building engines that at 3500 hours they are done! I don't think that Kubota is out of line at all with their BX tractors. ....

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2003-03-27          51998

I think Art hit the nail on the head with the quality point, it is far and away the most important point, second would be maintenance.

Years ago we purchased as a runaround, a Suzuki Samurai, pickup version, it was the funniest thing you imagine, the tin box out back was 4' square, and it had a whopping 650 payload, operator, passenger & fuel included. When it arrived I pointed out that it did not have a tachometer and instructed the staff to get the dealer to install one when it went back for the first inspection (oddly enough, after 25 hours of operation, regardless of mileage).

The dealer said no, it seems they weren't even OFFERED, when questioned the reply was "The engine is designed with a 12,000 rpm redline (it was basically a 1 liter motorcycle engine in a 4 wheel frame) and if you put the clutch and gas pedals to the floor it would only go to 9,000 rpm, so there is no need for one." The staff installed one themselves, and at first thought it was broken because it read 6,000 rpm at highway speed, 60 mph, which was floored. The tach. was NOT broken, and that little thing went 200,000 miles before being retired to an employees cottage as a bush-buggy where I'm told it still serves, although it does smoke a 'little' from oil consumption, this he states is his 'firewood-cutting-mosquito-repellent-system'. I doubt it's EPA approved, but I'm assured it works, either that or he's so high from the smoke he doesn't realize he's being bitten....

Best of luck. ....

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Art White
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2003-03-28          52045

Just for the sake of it I talked to a couple of old freinds that are still playing with pulling tractors locally here. They are turning up into the 7500 rpm range here and this is not the big boys mind you. It still depends on the engine makes as some will and some won't live at that or even at 5000 rpm. Some of them are turning lower rpm because they can't get the mass to spin well enough but load the torque on the pump with a big bulge. They have problems with bending rods. Buy heavier rods and they take out the crank, put in a ckank made of better steel and then they take out the block webbing that supports it. That is only if they can keep the heads bolted to the block tight enough to keep from blowing out the head gaskets. Gosh, it was a good conversation and it was with a orange (Allis) and a Red power man so we did have a little diversity there and a little chop busting but we did cover most all the current major colors locally. ....

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