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johnfundy
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2003-06-17          57863

I just read a reply on this board that stated the horsepower rating of an engine is less relevant than it's displacement. In essence, the comment suggested less horsepower from a large cubic inch displacement engine is better than more horsepower from a smaller CID engine. I disagree, but maybe there is some truth here. I understand "torque" as the act of doing work, frequently expressed in ft.-lbs. ( or newton-meters for Metric fans). I understand the rate of doing work per unit time, ft.-lbs. per second, is "horsepower". So where does engine displacement come into play?



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TomG
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2003-06-17          57881

There are quite a few discussions on this subject in the archives. I don't recall this one but I probably did read it. I can only guess the reasons behind the comment but there can be various valid ones. For example, other things being equal a relatively low HP engine/displacement should last longer that a high HP smaller one. High HP/displacement often is produced by tuning so peak torque occurs at higher rpm, which generally means more engine travel per hour of operation. Other means of increasing HP such as higher compression places greater stress on components like engine bearings which tend to be smaller in smaller engines.

The reasons may not have had anything to do with engine life but could simply be a preference for how low rpm engines feel when they're working. Big engines with low HP engines often produce peak torque in a narrow band at low rpm's. The torque may be greater than in higher rpm engines. They also tend to have more rotating mass that gives them better resistance to load increases. There's a bunch of things that can be said for old iron and many people prefer working with such engines.

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AC5ZO
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2003-06-18          57927

Tom pretty much covered it, but let me add a couple of things. Larger displacement engines deliver more torque. (Longer stroke is more important than bore size in an engine from the torque standpoint.)

Power or HP is the rate of delivery of torque to produce useful work and as such is essentially the engine torque multiplied by the RPMs and a factor to get the right units.

I have seen many tractor and engine specs where they will nudge out an extra HP or two by turning up the rated RPMs on the same basic engine by 10% or so. A 10% increase in RPMs increases the wear rate on the engine by 33%. (Wear is a factor of the cube of speed in RPMs) This is the wear rate during running, but in my experience running wear rate is less than the wear that occurs during starting.

Allowing the top engine speed to increase to provide a couple more horsepower does nothing to improve torque in the low end or mid range of the engine power. I don't know about you, but I spend much more time at mid-range of the throttle than I do at rated speed or full RPMs.

So, what does this all mean? A 28HP and 30HP engine might perform almost identically in the low and mid ranges if the engines are derived from the same basic mechanical block and have identical bore and stroke. The extra 2 HP may come from allowing the engine to rev out a little further.

One other example that you may recall relates to racing. You may have heard the term "qualifying engine." A qualifying engine is a very "hot" version of the standard racing engine. It will produce more peak HP with the same bore and stroke, but its life will be measured in minutes not hours. Its purpose is to put your car above the cutoff for the qualifing cars on raceday. You have to also remember that racing engines will get close to 1000 HP out of 2 liters of displacement by turning well over 10,000 RPMs, but they only last one race.

If a tractor manufacturer gets your business by specifying 30 HP over comparable models rated at 28 HP, then I suggest that you may want to look into this a bit further. ....

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buzst1
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2003-06-18          57928

Hi John,
I'm guessing your refering to my comment. The issue is that there is no easy way for a buyer to compare tractors based upon HP rating because there is no standard means for expressing HP. ie: would anyone believe a 24HP Sears lawn tractor as powerfull as a 24HP Kubota? The Mfg's have the ability to publish a HP rating based upon any rpm they desire, regardless of the fact that it may be on the down side of the torque curve. An example of this is a comparison of a kubota BX2200 and B7500. Because the published HP on the BX2200 is 22HP and that of the b7500 is 21HP many people actually believe the bx is the more powerful of the two tractors. If you examine the engine specs of the two machines you quickly find that the B7500 is a far more powerfull machine. Given that the technology of most of todays diesel engines is so similar, when comparing machines it really easiest to look at displacement to see which has the larger and "most likely" most powerfull engine. after potential choices have been made then you can compare the power curves of the engine to make a final selection. ....

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Chief
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2003-06-18          57937

I realize this is an orange conversation but here is some info. that applies to what you are talking about. Same thing applies to Kubota. I posted this in another forum on a conversation pertaining to the difference in power between the John Deere 4310 and 4410:



The 4310 engine (Yanmar 3TNE84) displaces 91.3 cubic inches. The 4410 engine (Yanmar 3TNE88) displaces 100.2 cubic inches. 8.9 cubic inches displacement is not a world of difference but certianly does add something. That something is a 9.1% increase in displacement and a corresponding increase in hp & torque as well as a 4mm longer stroke. This comes to 73.1 ft./lbs torque for the 4310's (Yanmar 3TNE84) and 81 ft./lbs. torque for the 4410's (Yanmar 3TNE88). That comes to about 9% increase in torques as well. Most would consider this a noticable and sizeable increase. Question is.......... is it worth the extra money to you?
....

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AC5ZO
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2003-06-18          57939

Even though the first question that a tractor dealer is going to ask is "What HP?; it is probably better to consider frame size and what you are going to do with the tractor. This puts you into a class that can use the right Backhoe, plow, FEL and so forth. The companies have done a pretty good job of matching the engines to the proper frame sizes. Competition selects the leaders. After you have selected a basic frame size you ask the question about whether more power is worth more to you.

With respect to the final selection of HP, you may want to also consider the standard hydraulic flow capacity and other things that might guide you. If you have a choice of engines, I personally would choose the slow, long stroke version. In my case, I live at over a mile above sea level and engine HP is lost. That can be made up for with more displacement.

BTW, I was not referring to anyone's comments outside of this immediate thread. I do not have a Kubota but this question came into my area of interest so I responded. ....

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DRankin
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2003-06-18          57950

Ok. I am NOT trying to stir the pot here, I just want a bigger perspective.

I know that a well made, well maintained diesel pick-up engine can go 250,000 miles...... what is the RPM range for these engines?

And, does anyone know at what RPM range diesel car engines such as VW's and Audi's run?

I am thinking that my BX engine running at 3200 RPM (max) can't be all that unusual or all that fast. ....

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Chief
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2003-06-18          57959

My Cummins is set to limit fuel at 3250 rpm. I rarely take it above 2800. Never need to. I makes 505 ft./lbs. torque at 1800 rpm. With a reflash or a chip/box it can go to 660 ft./lbs. and much more. 75 mph = about 2000 rpm. ....

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Art White
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2003-06-19          57993

Horsepower and displacement has little to do with each other as far as a relationship. When the word torque enters in then it changes. Normally bigger is more at this point. There are so many variables here, my sled has 800cc and produces 160 horsepower. Thats about 50 cubic inches, that's good horsepower and virtually no torque. ....

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AC5ZO
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2003-06-19          58002

Diesel engines and other engines for that matter will last for a very long time with good lubricant and long running. In my experience it is starting the engine that has the worst effect on wear. This is especially true of engines that are not run for quite a while. I have even used engines where you can pressurize the oil externally before starting it.

The oil film on cylinder walls will thin out after a time of draining. The oil film in the journal bearings will also thin out. When you start the engine, it has little lubricant until the oil pump gets it flowing and the crank gets some oil into the bottoms of the dry cylinders. This is why I personally use the best synthetic oil that I can find. I am not trying to start an oil debate here.

What I said about wear rate being the cube of engine speed is true, but if the wear rate is very small to begin with a 33% increase may not show up in practical terms. But, when selecting the engine for my tractor, I want the torque. That means more cubic inches.

Mark, you live at about the same altitude as I do, I think. At 5300 ft, my engine only produces about 85% of what the published specs say. I still vote for more cubic inches.

Changing the chip or programming of an engine affects the fuel usage primarily. But, there is a limit to how much fuel you can burn in a given engine cylinder and how many RPMs you can safely run. ....

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Jelliott
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2003-06-19          58005

This is slightly off topic, but I have to take exception to a statement that appears earlier in this thread, and in lot's of other places here on the Compact Tractor Discussion Board. The statememt I'm referring to goes something like this "some manufacturers turn up the RPM to get a few more HP". Given that HP is an emperical derivation based on torque and RPM, this may seem to be a reasonable statement, however, at or near max rpm's the torque curve typically has fallen off such that more rpms will actually result in less hp.
Hp = (2 x pi x rpm x torque)/33,000 (not 100% on the 33,000 figure, been out of schoo lfor a while), therefore torque and rpm contribute equally to hp, if torque is falling faster than rpms are rising, hp goes down. How many engines have you seen that develop max hp at the max rated rpm? ....

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AC5ZO
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2003-06-19          58009

You are not wrong with what you say, but the conclusion that you draw is flawed.

For example: 2600 RPMs may be a rated speed for a tractor engine. At that speed the tractor will deliver a 540 RPM PTO speed. This is not the maximum RPM of the motor or the speed at which the engine will develop horsepower. The maximum speed of my engine is controlled by my fuel delivery system. At full throttle, my tractor engine is only going to deliver about 2800 RPMS before it stops climbing. (Don't try this with your car.)

If you change the gearing and fuel systems so that the same physical engine will run at 3000 RPMS it will develop quite a bit more HP. The gearing has to be changed to still deliver 540 PTO RPMS. This engine that has been "turned up" will still deliver about the same torque curve up to 2600 and with the higher ratio gearing it will produce more torque at lower ground and PTO speeds. (If it can be used.) It will not reach rated HP till it gets to 3000 RPM.

If we took this a step further, that same engine may continue to develop even more HP if we let it go as far as 4000 RPMs and had a fuel system that would accommodate it. This is what the Tractor Pullers do in some competition classes.

Peak torque "peaks out" and starts to decline before peak HP is reached. If you continue to run the engine at still higher RPMs, HP will also decline, but rated speed and power on a tractor engine are nowhere near the peak capability on that physical engine. ....

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Murf
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2003-06-19          58013

Mark, earlier in this thread you asked the question "I know that a well made, well maintained diesel pick-up engine can go 250,000 miles...... what is the RPM range for these engines?"

Well, I don't know if you meant 250,000 miles as a benchmark, or just an example but we have a Ford F-450 at the farm which was purchased and has been operated strictly to haul trailers, equipment floats originally, for my business, then after 5 years of that it was off to the farm for 'retirement'. It is now 14 years old, has approx. 600,000 miles on it and still earns it's keep. Maintenance schedules were and still are strictly followed, and every 100,000 miles it gets a rebuilt injector pump, injectors, an oil pump and turbo.

The final drive ratio is a steep 5.13 to 1 so speeding is not a problem, in fact the engine rpm's hit the governor at 3450 rpm, which happens at about 65 mph in 5th gear (overdrive), and at about 55 mph in 4th gear (direct).

I would say that of all the miles on it only a very small fraction of them were NOT at 3450 rpm.

Best of luck. ....

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DRankin
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2003-06-19          58018

Thanks Murf. If my BX engine goes 15,000 hours that's about 100 years at my current rate of usage.

I'm thinking I don't have much to worry about. ....

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TomG
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2003-06-22          58111

There is a thread in the archives from a couple months ago where HP and torque were calculated at various points on a power curve for a current model JD (from JD site data). There also are some comments about the merits of traditional low rpm high torque/narrow power engines vs newer broader band higher rpm engines like MarkH's BX. The thread was interesting and relevant here. Wish I could recall the subject title. ....

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DRankin
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2003-06-22          58140

Is this the one you were thinking of Tom? ....


Link:   

Click Here


 
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TomG
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2003-06-23          58148

Thanks MarkH that's the one under the subject 'BX Engines.' I never would have remembered it. We sure did hash out the subject pretty good. It never occurred to me to copy the address when in the archives and use it for a web link.

For anybody who notices a formula in the discussion
HP = (Torque x rpm)/5252
It is a calculating formula that gives the same results as Jeliott's formula, which is in foot pounds. Another version gives results in inch pounds.
....

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Foghorn
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2003-06-23          58157

I was looking at the specs of my orange 2910 and the blue TC33D:

2910
4 cylinder
Gross HP 30
PTO HP 22
Displacement cu" 91.5"

TC33D
3 cylinder
Gross HP 33
PTO w/ hydro trans 26.9
Displacement cu" 91.3

I haven't see a curve chart for these two engines but could someone explain the difference in HP since they basically have the same displacement. Does the blue turn a "higher" rpm so to speak?! I would think the orange would be a smoother running engine since it has 4 cylinders. Would the blue with bigger pistons therefore give the feel of more torque?

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AC5ZO
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2003-06-23          58159

Displacement comes from both bore and stroke.

Torque (especiall down low) is more associated with stroke length than bore size. High reving engines will generally use shorter strokes for a given displacement and less low end torque.

I don't have the specs on either of these engines, but the overall power is a factor of many things. If you know the "rated RPM" then it would help. Since the NH engine will have about 33% more displacement per cylinder, I suspect that both the bore and stroke are larger on Blue.

As far as smoothness is concerned, straight three and six cylinder engines are quite smooth because of where each cylinder delivers power in a complete rotation. Four cylinder engines generally have two power strokes per revolution that are 180 degrees apart. Either engine can be very smooth and well balanced.

Most engines will deliver torque that will peak out at a particular speed and then start to decline slowly. In most cases, peak HP will happen after peak HP because engine RPMs rise more rapidly than torque falls off. Tractors are rated at "rated speed" which is less than peak HP that could possibly be achieved by "hot-rodding" the engine. ....

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DRankin
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2003-06-23          58161

I can't find the exact specs for the TC but the B2910 is a "square" engine: Bore and stroke are both 3.1 inches.

The RPM assumption is correct. The Kubota is rated at 2600 rpm and the Boomer is rated at 2800. ....

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AC5ZO
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2003-06-23          58165

The extra couple hundred RPMs and the higher torque from longer stroke are enough to close the case.

The rated RPM difference alone could account for 77% of the difference without looking at Torque curves.

The only other point that I find curious in this comparison is the difference in the PTO HP. The Kubota is down 8HP and the NH is down 6.3 HP. That is over 25% difference for the Kubota and less than 20% on the NH. Do they rate their PTO HP at the same speed that is used for rated HP??? ....

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Foghorn
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2003-06-23          58166

If my calculations are correct, the 2910 makes 60.6 ftlbs of torque at 2600 rpm and the TC33D makes 61.9 ftlbs of torque at 2800 rpm. That puts the two tractors a lot closer together then if you were to just look at the HP. ....

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TomG
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2003-06-24          58201

Sure would be handy if there was a table showing the rated and pto rpm's for both tractor and the torque at those points. Differences between the size of any gap between rated and pto rpm sure could account for the difference but so could different transmission efficiencies.

Specs sure are confusing. I hopped in the JD site simply because I knew where to look for specs. For a 4310, they give separate specs for advertised and official PTO HP at RATED RPM, and standard and maximum PTO HP at ENGINE RPM. However, all of them are 27/25 at 2600 rpm (guess the 27/25 is a range or maybe depending on the TX). Gross engine HP at RATED SPEED is given as 32 at 2600 RPM (wonder if rated speed is different than engine rpm).

I couldn't find the torque/rpm charts I remember but I'm pretty sure that rpm's above 2600 would produce power above 32 engine HP. Anyway, it sure would be tempting for a marketer to advertise at max HP RPM rather than a lower pto rpm but JD doesn't seem to do that. I'm not sure why manufacturers bother with gross engine hp anyway. It is perhaps the least related to a tractor's ability to do work of any common power measure.

Foggy: Right or wrong, I use a concept that torque is a measure of force and HP a measure of work. The thinking probably comes from junior high physics. When discussing ergs or some sort of measure I was surprised to learn that something has to move for work to be done. I could push on a rock all day and perform no work unless it moved. My reaction at the time probably was 'Yeah right.' To me torque is most useful as a measure of an engine's ability to resist load changes. Of course a heavy flywheel also resists load changes and I don't know if torque measures are taken with of w/o a flywheel. I don't know if all this helps or hinders interpretations of this stuff.

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Foghorn
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2003-06-24          58205

TomG, I didn't take physics but I did take statistics and what I learned from that course is that one must compare apples to apples to get a halfway decent comparison : ) I don't have much experence with tractors but I'm sure whether it's an orange/blue/green etc... for what I'm going to use it for any of them would do just fine!

Thanks to all of you knowledgeable members for the advise/comments/suggestions... foghorn

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AC5ZO
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2003-06-24          58210

Tom,
Torque from an engine is the ability to make force through the wheels or other transmission mechanism. Horsepower is the rate at which the engine can make a particular force or torque and is generally = torque X RPM X factor. (factor is only to change units of Power) Inertia is the resistance to change in speed and is a basic property of flywheels and other masses.

The engineering concept of "work" is troubling to many including new engineering students. But it is a semantic issue and you get used to the venacular. There are others like that; speed and velocity have slightly different meanings, for example.

The question that I posed earlier about the difference between PTO HP in the two brands could be due to efficiency or it could be due to the way the specs are written or both.

Foghorn, I think that you have it right. You pick a tractor in a frame size that fits your application. The difference in most of the engine variants in that frame size may come down to how fast you can accomplish a task, but all will finish the job. ....

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Chief
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2003-06-24          58214

You know how the ole' saying goes ..... "Liars figure and figures Lie". ;o) Each manufacturer wants to present their specs in the best light. ....

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DRankin
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2003-06-24          58232

I might be too trusting, but it does not appear to me that anybody is being hoodwinked by any major manufacturer.

If you peruse the numbers across the board they generally match up pretty well with the displacement/horsepower ratio.

The ones that don't have a reason.... they run in a different (higher) RPM range. And if that is bad for a tractor diesel, why is it ok for a car or pick-up diesel?

I have a tach on order for my BX, so I can't say for sure yet, but I think I run it about 2600 rpm's 90 percent of the time anyway.
That rpm setting would net about 6 mph ground speed in top gear, which would shake the pee out of you on most of my land.

Running the backhoe anywhere above half throttle is a waste of fuel and just results in it banging into the stops.

I guess I am saying it is pretty much a non-issue no matter which way you view it. ....

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TomG
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2003-06-25          58243

Yep I agree. Tractors are engineered to deliver draft. Tractors mostly pull things. There is a relationship between power, weight and size to do that job, and all manufacturers design them about the same. A person could cut through all this specs stuff by simply selecting the width implements wanted and then buy any tractor that they like with that width rear tire tracks. I guess that sizing a tractor to a shed wouldn't work that bad either. I suppose there could be a theory developed that relates the size shed needed to property size but I'm not too serious here.

Chances are that the tractor a person really likes is going to be the right one for them, and specs can be pretty much ignored. Well, 'one size fits all' doesn't quite work for tractors. The best machine to mow the lawn may not do heavier work that well. Lifting and trenching can impose some absolute limits that 'taking more time' won't solve, but minor differences in HP and torque specs really don't address these issues very well. I think most specs are for advertisement or to satisfy consumer law, and they aren't that useful for choosing a tractor.
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TomG
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2003-06-25          58244

AC: I was trying to reduce concepts to practical terms (hard for me I know). If a tractor is doing work, meaning moving things, then it is HP that is important. Torque is relevant only in that it's torque that makes HP at a particular rpm, or at least that's the way I think of it.

I also was trying to get the idea you sometimes hear that a high torque/low rpm engine will pull you though hard spots where other engines will bog down. I don't know if that is true but it does seem to be the heart of the torque vs HP debate. I suppose that if load exceeds HP delivered the engine slows down pretty fast as inertia comes out of the system, and HP is further reduced as rpm falls. Most operators then take some action to reduce load and then the whole thing is what happens after the load is reduced.

I suspect that most high-torque/low rpm engines have a narrow power band so that HP comes back faster if rpm increases (I've heard of that called a 'torque kick). I was wondering if these engines might have better resistance to load increases irrespective of inertia? The idea may be contained in a spec called 'percent torque rise.' I've seen that spec for farm tractors in the Nebraska Tractor Tests but not for compacts. I don't know how to interpret that spec. Despite my previous trashing of specs, here I am introducing another one. Go figure, but we're in a heat wave here so that's my excuse.
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Art White
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2003-06-25          58245

It sure is fun reading here! To think that on most of the engines you are comparing can be altered a little and change the whole package. Thing is will the engine hold together when you take a engine and bump it's torque load up? Some will some won't! There is more here than just a few formulas that you can throw numbers into. The manufacturers all have a prorated life built in. That tells them how far they can go and what they will have. The D-414 engine used in the IH 1066 one of the hottest tractors built,was rated at 115 horsepower was most efficient at 50 horsepower. Go figure! ....

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Misenplace
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2003-06-25          58253

This is certainly a good strand. Initially I thought I could add something but after reading TomG and AC5Zo's input I believe they really hit the nail on the head in the first two posts. Mark on My duramax at 75 mph I am turning a little over 2k rpm. I certainly don't think any of us on any of theese engines with normal care and maintenance have much to worry about as far as longevity. I have done the math on the hours and mine should easily out live me as well. I do think however if you are to compare any CUT tractor engine to any truck engine this entire strands validty is multiplied. That is too say overall mass, Displacement and stroke must be compared. I would not think the CUT engines would last nearly as long under the same conditions as Chiefs Cummings, nor would the Cummings hold up against Murfs F450. But then your tractor should still easily out live the both of us so it is splitting hairs a bit. I do think it is easy to get a little tied up in the stat zone when first time buyers are shoppng for a tractor Although I personally, even with a pretty strong mechanical background find the weight Vs. Horsepower/Torque debate a more aloof comparison with out experience in the saddle. In reference to the manufactures tweaking specs we could also add Marketing to the mix. I have the JD 2210. 23 hp and yet it is so light that it is hard in most situations to benefit from it as the tractor simply does not seem to weigh enough to utilize the full power band and the transaxle is not cast iron but aluminum alloy. ....

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Peters
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2003-06-25          58258

I have been reading this post along the way and am not sure I can add much.
Tom most of the high torque engines have a fairly wide power band that starts at near 500 rpm and goes to 2000. If the HP is 25 at peak you can see that the available torque is much higher than a 25 HP engine that has a band from 2000 to 3000 rpm. In most tractors you can not change gears without stopping and selecting the next gear. Therefore if you loose power you can either slip the clutch or stop, add fuel or stop and grab a lower gear. For example when I mow with my low rev MF 65 as I power up the hill I simply add fuel and the old tractor powers through the hill. With the JD I must have the correct gear at the bottom or as the rpms slow I do not have enough torque to pick the rpms back up by adding fuel. It is difficult to determine what gear you need to be in before you load the tractor therefore the higher torques is preferable. Naturally if the the tractor is hydro then the analogy changes you can easily slow the tractor and keep the RPMs up. If you look at the power bands on the hydros you will see that they are set differently.
Doc you can see that the 2000 to 3000 rpm engine has a better power to weight. The lower RPM engine must be built much heavier to accomidate the higher torque. But as you have stated power to weight is not that important on a tractor. ....

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marklugo
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2003-06-25          58261

Okay,
I think everyone seems to agree on horsepower determination. After researching it and trying to remember from my school days, does anyone of you "engineers" know a formula that can be predictive of torque. I know it is a measurable element of figuring horseower. However, if HP is not known may one be able to figure torque based off bore, stroke and total dispacement? I can't recall any discussions other than the HP formula given. ....

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Chief
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2003-06-25          58266

Hey Doc, the Cummins engine is an optional upgrade engine in the Ford F-450 and up trucks. If Ford had offered it in the F-350 series, I would be driving a crew cab F-350 right now. The Cummins ISB series engine comes stock in power ratings all the way up to 275 horse & 660 ft/lbs. torque. Just takes a reflash of the ECM by Cummins if you have the green backs and don't mind voiding the Diamler Chrysler warranty. ....

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Jelliott
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2003-06-25          58267

Chief,

That would be the F-650/F750 that offer the Cummins ISB as an option. I've got 275 RV injectors, and a mild aftermarket timing/fueling box (edge EZ) on my ISB. My warranty is toast, but I've got gobs of power! By the way, I'm not making the extra HP by spinning at a higher rpm. The entire torque curve shifted up around 100ft lbs (got before and after dyno runs to prove it). From my experience in 'turning up' diesel engines, this is usually the case - dump in more fuel & the torque rises across the board. Max torque/max hp occur at roughly the same rpm. ....

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Chief
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2003-06-25          58268

Jelliott, good call! You are right; it is the F-650 and up. You have the automatic or clutch? ....

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Jelliott
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2003-06-25          58269

Chief,

Here are the specs on my rig:

2001 Ram 2500 quad cab 4 x 4 (like you, would have bought a ford crew cab if it had the cummins).

Cummins ISB in 'ETH' trim (ETH is the high output version 245hp/505 ftlb torque).

NV5600 six speed tranny.

Truck is stock except for edge box and injectors. ....

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AC5ZO
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2003-06-25          58284

Tom, as Peters said, most Low RPM High Torque engines are very flat on their power band and produce a lot of torque over a wide range of speeds. For racing, we quite often try to get max HP out of the engines at the cost of low end torque and engine life. I have had dirt bikes that put out more HP than my tractor, but some of those dirt bikes don't have enough low end torque to start from a standing stop on a steep grade.

MarkLugo, there are no easy formulas for engine HP or torque based on the bore X stroke, or other simple factors. You have to include compression ratio, valve timing, injector timing, fuel volume, and a host of other variables that makes this a difficult task. There are general relationships between stroke and low end torque, for example, but eventually stroke length interferes with the RPMs that an engine can turn. There are other such relationships between engine setup and HP, but they all result in a compromise of sorts.

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AC5ZO
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2003-06-25          58286

Mark H.
I am not trying to say that a tractor engine is going to "wear out" significantly sooner because of speed. The formula that I quoted is correct, but even if wear is increased by 30% with a 10% increase in engine speed, it is all factored against the wear rate in the first place. If the wear rate is "next to nothing" to start with, 30% more is still "next to nothing".

It is much more likely that I might want a new shiny tractor and buy one for that reason than it is that I will wear mine out. I have a good bit of experience with engines and here is my short list of engine sins:
1. Lack of Maintenance and Cleaning;
2. Dirty oil and fuel;
3. Excessive Starting;
4. Lugging.

I believe that any of these and probably ten more things that I did not list can shorten the life of a properly designed and manufactured engine by several fold compared to wearing it out through normal usage. Notice #4; Lugging. More people will probably damage engines from running them too slowly under load than will wear them out due to high speed. I mention these four things, because they all have the effect of harming the lubricant film on the bearings that protect the engine from excessive wear.

I use 1500 to 2000 RPMs for most of the work I do. I set the brake and shift to neutral rather than shutting the tractor off when I get off the tractor for a quick hookup or intervention.



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TomG
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2003-06-26          58346

I'm inclined towards Art's point that maybe how a tractor works is more important than it's specs and that minor engine differences can change the specs a lot. I think that a 30HP and a 33 HP NH engine are almost identical except for the governors.

Regarding the torque and HP stuff: Apples should be compared to apples. Pick a narrow enough range and most any distribution is flat. A better comparison might be the same rpm range centered on the rpm where an engine produces max torque. I think wider power bands tend to be defined for newer engines. From that perspective the torque curve on many older engines may not look flat at all.

I do believe that for similar HP engines, low-rpm ones would have higher torque (almost by definition) since they can't run much faster to produce higher HP's. They also would have flat curves since rpm's can't be varied much to make very wide ranges. As is often the case, everybody seems to be saying pretty much the same thing.

I don't exactly understand Peters's comment about adding fuel. The Massey may have different type governor than I'm used to. I believe mine is a constant speed type that attempts to maintain the rpm set with the hand throttle under varying load conditions by changing the throttle. I assume that the governor gives me full throttle in high load conditions. Peters comment makes the important point that operators of geared tractors should use a gear that they know will get them to the top of a hill. I probably could shift down with my synchromesh TX but I'd just as soon not have to try it.



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Art White
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2003-06-27          58424

Just to talk a little fun we had here a few years back, We took a 1466 IH tractor and cranked the torque screw all the way, had 165 when getting to rated RPM and held it to 225 horsepower when at the rated RPM. We did the same with the fuel screw and had the same results just a little more haze on the exhaust. That particular pump will only push to 225 horsepower in it's original state. We have had fun, taken to soft of iron engines and destroyed them with being to tight and installing to big of turbos and destroyed crank and rods. We have spun them to over 5000 rpm and had no failures on some and wouldn't dare to go past 3000 on others for fear of disintegration even on standard fuel delivery systems. ....

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TomG
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2003-06-28          58466

The calm wise voice of our stalwart dealer here did come after having wild and woolly tractor pulling days. I've heard the voice at least once before and I'm more used to it now. But what's a torque screw? I can guess the fuel screw adjusts the governor, and governors on most compacts nowadays aren't readily adjustable. Maybe torque screws have to do with turbo boosts, which is something else most of us don't have.

Fun stuff to play with for sure. I didn't have access or money to do serious engine building during my wild and woolly days. But I did learn that putting one or several pieces of speed equipment on gas engines don't usually make them any faster. The exception is milling the heads.

Almost everything on an engine affects torque and HP, and all these things are designed to work together. The twin 4-barrel manifold I spent my young life-savings on did look and sound good however.

Diesels are a bit different I think--perhaps because they are usually designed for fairly low rpm's and there's more room before other bottle-necks become limiting. In normally aspirated diesels, rpm is mainly determined by load and fuel delivery. Turn up the fuel and they just keep going faster and the HP goes along for the ride until things start flying apart I guess.
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Art White
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2003-06-28          58469

Sorry Tom, The pumps used on those engines allowed manual adjustment of both fuel and torque, both the same but yet different. The fuel gave more fuel all the time, the Torque screw increased the torque by adding more fuel much the same but different. Both torque maximum and horsepower were normally the same just depends on who waas driving the tractor and the best way to make them live for the driver. Todays tractors do to a tougher environmental arena have fewer adjustments that might be able to be made by a dealer or owner. Many pumps today have shim packs that get changed to accomplish what we used to do with a 7/16th wrench and a screwdriver. The new way requires removal and disassembly of the pump. No more 5 miniute tune-ups for an additional 100 horsepower. Years ago with injection systems on auto's you could buy aftermarket units able to be fully adjusted like these diesels were. My point is you still have engines designed and built that can handle the RPM and torque increases and you have them that can't. The metel used in some, and the the design priciples used are not condusive for long life at more than the manufacturer sold it as. That means they could not live for one hour of spinning at 5000rpm much less ever reach it without greanading. Any fuel you add over the original pump setting will send plumes of black unburned and partially built fuel to the ozone as the head and piston designs are that inefficient even just for a simple 10 horsepower gain. ....

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TomG
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2003-06-28          58473

Thanks! It sounds like the difference between changing the governor calibration, which changes the fuel delivery at any given rpm or changing the max throttle position. Today, most of us have some control over the max throttle position through the max no-load rpm adjustment but the calibration requires shim or different governor weights. If the pumps, rather than the governors can be adjusted, then I'll be learning something. In practice, I just stick with the factor adjustments because I almost always run out of traction before I run out of power anyway.

Around here you still see some logging trucks that may have given rise to the expression 'dumping the coal to it,' although the expression probably actually came from steam engines. Black smoke rolling out of them is a sure sign that the fuel has been turned up or the drivers are running them seriously hot.
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Misenplace
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2003-06-30          58598

With out re-reading the entire strand I think someone asked for a formula to determine Cu in of Diplacement. The formula is pi x (bore/2) squared x stroke = displacement ....

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AC5ZO
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2003-06-30          58600

I think that the question was about "what formula you could use to determine torque for a given engine?" I said that there were no stock formulas only things that you could do that caused HP or torque to trend in one way or another.

Torque is technically going to be :
Combustion Pressure = CP
Piston Area = PA
Friction = F
Stroke = S
Engine rotation angle from TDC = A

((CP x PA)-F) x S /2 x sine A = Torque

This is the torque from a single cylinder. Three, four, six and eight cylinder engines can deliver torque more smoothly by having more power stokes per rotation. Average torque is smoothed out by the engine flywheel and other moving parts of the engine.

The reason that there are no stock formulas for determining engine output is that the combustion pressure changes during the rotation of the engine and due to changes in fuel volume, ignition timing, air volume, compression ratio, cooling, valve timing, burn rate and so forth. ....

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Misenplace
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2003-06-30          58603

I see, and you are right there are no standard Torque formulas. I do however have the Formula for the Correction factor to determine Torque in a standardized Dyno but I wouldn't begin to know how to post it. It primarily relates to Dry air pressure and ambient temperature to get a standardized reading Vs. High torque on a cool day or low on hot. ....

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AC5ZO
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2003-07-01          58618

The formula dealing with standardizing dyno readings basicly adjusts for air density. I have done this for my tractor.

Altitude, temperature, and humidity all affect how much torque and HP you can develop in an engine. For example, I am at 5300 ft above sea level where I live and the air density is only 85% of what it is at sea level. Up to a certain altitude, you can use this number directly to calculate engine output by multiplying the density percentage by the dyno HP.

So, my 45 HP tractor will only deliver about 38 HP. Here again more displacement saves the day. ....

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