Three cylinders? Or four?: John Deere Review  -- John Deere Tractors Discussion Forum and Review Three cylinders? Or four?: John Deere Review -- John Deere Tractors Discussion Forum

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 02-02-2000, 00:00 Post: 12465
Roger L.



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 Three cylinders? Or four?

Reading through some of the messages lately, I see that some tractors are offered with three cylinder engines and others with four. The perception seems to be that "more is better"....or maybe it is simply that there is a bias in favor of even numbers of cylinders. Is there really any difference?






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 02-03-2000, 00:00 Post: 12471
Tom G



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 Three-cylinders?-Or-four?

I think the usual take on cylinder numbers is that more adding smaller amounts of power in more places around the circumference of an engin's rotation makes for 'smoother' power.

You can get much the same effect by using a heavy fly wheel. However, an engine with more cylinders may have better ability to pull itself out of a lugged down condition. I don't know this, but I reason that a heavy rotating flywheel has inertia that helps sustain rpm during high load conditions. But, when an engine is loaded to the point that it starts loosing rpm, inertia in the flywheel is lost as well. It takes power to restore that inertia as rpm increases under a lightened load.

Of course, all rotating components in the drive train have inertia. The flywheel is just one component. I'm guessing that designers can get good performance with lighter rotating weights if more cylinders are used. On the other hand, inertia is lost with reciprocating motion. Engines with more cylinders have more reciprocating motion.

Probably a mechanical engineer knows the answers that I only guess at. What I do know is that overhaul costs are a lot higher for engines with more cylinders. I also know that small numbers of cylinders do work. At least I think my grandfather used something called a JD 'one lunger' for many years, although I don't think I was able to count cylinders when I remember seeing the tractor.







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 02-03-2000, 00:00 Post: 12480
Murf

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 Three-cylinders?-Or-four?

There is at least one more major difference with more cylinders for a given displacement size. The more cylinders you have firing, the less power each individual cylinder must produce, therefore less heat and more efficiency. In extremes of temperature, or when running at maximum power this becomes very obvious. It also likely adds to the life of the machine, since each cylinder doesn't work as hard or as often (30% less with 4 cyl. instead of 3cyl.). The most noticeable however is the response and smoothness.






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 02-03-2000, 00:00 Post: 12490
MichaelSnyder

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 Three-cylinders?-Or-four?

Humm...I don't mean to be a blooming idiot, but I'm struggling to understand how 4 cylinders work/fire 30% less than a 3 cylinder. It's always been my understanding that each cylinder in a 4 cycle motor ignites fuel every other revolution of the crank shaft, OR every fourth cycle of the piston travel. So I not sure how this creates any type of % ratio. Regardless of cylinder quantity, internal combustion happens once every four cycles in each cylinder. I will definitely agree that response & smoothness increases as cylinder qty increases. But I'm struggling with the "more is better" concept. If this were true, why are most large farm tractors using straight six cylinder blocks??...To be honest, I think most construction pieces use I6's. I'm not trying to start a dilema..just trying to clear up my confusion..






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 02-03-2000, 00:00 Post: 12498
By the Brook Farm



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 Three-cylinders?-Or-four?

Engineering 101..energy is neither created nor destroyed. It is transferred. A hotter engine is more efficient, not less efficient. The hotter the better. Trick is to have it last without melting. More cylinders are smoother running because the ignition can be staggered around a 360 degree circle more equally. To wit: hop on a harley davidson, then hop on a 6cyl Goldwing. Feel the difference? On the two cylinder bike your fillings are falling out and on the 6cyl you think you are driving a Buick. More is better up to a point, and the point is right around 6 cylinders..that is why the big boys have 6cyl tractors. Of course there are about a zillion exceptions to this very basic outline but that would lead us to something like engineering 405..anyway, the bottom line is that more cylinders usually will equal a smoother running engine.
Take a BMW 750iL out for spin to see what I mean..then hop in a GEO Metro. Exercise would not be that noticable if you went from a 3 cylinder JD4400 to a 4 cylinder JD4600 running all of 2,000 rpms.






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 02-03-2000, 00:00 Post: 12500
CHRIS



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 Three-cylinders?-Or-four?

I have to agree with Brook. The 3 cylinder JD4200 ran as smooth if not smoother than the 4 cylinder kubota 2710 when I test drove them. Im sure there is a difference but at 2000 to 2600 rpm I couldnt tell it.






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 02-04-2000, 00:00 Post: 12503
Tom G



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 Three-cylinders?-Or-four?

Couple of notes: A hotter engine is more efficient. The power of an engine comes from expansion of input gases. Basically, you add fuel to air so you can get the mixture to expand a lot. A hotter engine means the mixture expands more. It's easy enough to engineer engines to operate at much higher temperatures than a typical 190F. In fact, I think WW2 British Spitefires were vapour cooled. They got more power from operating at higher temperatures, and they could use smaller cooling radiators.

One cylinder can be real smooth. I was near some oil fields in central California and heard this 'bang' 'bang' every five or ten seconds. I believe it was an engine that runs oil pumps. Never was sure, but it seemed to be a single cylinder engine that fires every 5-10 seconds. Guess that could be done with a fly wheel where the weight is large in comparison to the load. Just get the fly wheel spinning, and the engine bangs away occasionally to keep it going. The power would be real smooth. However, I imagine that such an engine would work well only with fixed loads, like pumps.






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 02-04-2000, 00:00 Post: 12507
David Paul



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 Three-cylinders?-Or-four?

Engine Efficiency = Thermodynamics
All internal combustion engines (gas or diesel) are subject to the laws of thermodynamics. They are heat engines and you increase the efficiency of a heat engine by lowering the exhaust temperature. There are a number of ways to accomplish this, one is as posted above is to run the engine operating temperature hotter (keep more heat in the engine), this works up to the point where the metal parts the engine is made of start to weaken or melt or the oil begins to breakdown for high temps. Another way with diesels is to turbocharge, convert heat in the exhaust to mechanical work to force more oxygen in the engine for more complete combustion of the burning fuel. If you measure exhaust temp in and out of a turbo you will find the exhaust is cooler (energy has been extracted read free HP) This increases the overall efficiency of the engine. Most internal combustion engines waste most of the energy in the fuel as excess heat that is dissipated thru the radiator or out the exhaust pipe. Diesels are more efficient than gasoline in the conversion of heat to work due to their high compression ratio and more BTU per gallon of fuel. That is why diesel trucks get more MPG than a similar gas model. HP is HP and it doesn't matter if ii is made with a 2 cyl or 6 cyl engine. Yes there will be differences in smoothness, as you add more cylinders the are more smaller power pulses per crankshaft revolution. This is what is felt as smoothness. With tractors fuel efficiency is an issue. An engine with less cylinders will generally be more efficent than on with more for a given HP level. The most fuel efficient traqctors ever built were the old JD 2 cylinder diesel models. That is one reason there are a lot of 3 cylinder engines out there in tractors. 3 cylinder engines also lower manufacturing costs over 4 cylinder due to the reduction in the number of parts required. There are lots of 6 cylinder engines for the same reasons. 2 less cylinders than a V-8. Bottom line is if the engine is well engineered and made from high quality materials it really doesn't matter if is 3 or 4 cylinders






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 02-04-2000, 00:00 Post: 12509
Murf

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 Three-cylinders?-Or-four?

Easy fellas, read the messages CAREFULLY, then reply...Laughing out loud...I said "less heat AND more efficiency" NOT more efficiency BECAUSE OF less heat. As far as % goes the logic is 40hp from 3cyl. is 13.3hp/cyl. whereas 40hp from 4cyl (like my Kubotas have) is only 10hp/cyl., therefore each cylinder is producing 3.3hp less and therefore working easier to do the same task. As for the heat issue, because there are 33% more cylinders (and more block to dissipate the heat), working 25% less each, it is not as difficult to keep the engine cool under load or in high ambient operating temps. I did not intend to infer that the engine operated at a lower temp. or that a lower operating temp. is more efficient. The bottom line, more cyl. working less each will outperform the same displacement with less cyl. every time, just ask the guy down the road who found out that my V12 Jaguar blows the doors off his new 'Vette....






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 02-04-2000, 00:00 Post: 12513
MichaelSnyder

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 Three-cylinders?-Or-four?

Ok.OK...I re-read the thread CAREFULLY.. (Murf says: since each cylinder
doesn't work as hard or as OFTEN (30% less with 4 cyl. instead of 3cyl.))
As my post indicated, I wasn't questioning the basics of "distributed load principle", just didn't understand the "often" part. As far as more cylinders being superior when comparing equal displacement...Again, my experiences cause me to disagree, If your statement held true, why do smaller 5.9L 6 cylinder Cummins not only keep up to, but pass larger 7.2L V8 Powerstrokes?? Yet..I fully expect a Powerstoke owner to respond and say "I can blow the doors off a Cummins".. And to be honest I would expect that a 7.2 liter engine would wipe up a 5.9L. Even though..time and time again, I've seen the 5.9L Cummins prove otherwise. One more note, Engines holding the record for highest HP output per Liter or CID are either 4 or 6 cylinder. Can't say I remember seeing any 12's holding those records. Although I've been wrong many times before. Of course now I really did it..I went and started the "Mine is better than yours" dilema...Why can't people understand the concept of something being designed to serve its intended purpose...Why does everything have to be a better or worse issue. So...how does a Jet engine compare to internal combustion 24 cylinder motor using......






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Discussion Boards > Active Subjects > Messages as Posted > John Deere Review Forum

Thread 12465 Filter by Poster:
Bird Senter 1 | By the Brook Farm 2 | CHRIS 1 | David Paul 1 | MichaelSnyder 3 | Murf 4 | Nuclear_Weapon7 1 | RBinNC 1 | Rick Seymour 1 | Roger L. 3 | Tom G 3 |




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