4 cyl. vs. 3 cyl. diesel: Kubota Review  -- Kubota Tractors Discussion Forum and Review 4 cyl. vs. 3 cyl. diesel: Kubota Review -- Kubota Tractors Discussion Forum

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 09-07-2002, 22:16 Post: 42136
E. WOZ
2002-09-07 00:00:00
Post: 42136
 4 cyl. vs. 3 cyl. diesel

I'm looking at buying a tractor in the 30hp range. I've noticed that the Kubota B2910 has a 4 cyl. diesel when the New Holland and the Deere have only 3 cyl. engines!! Is this a big issue that I should pay attention to?? Does the 4 cyl. have more torque than the 3 cyl.?? They never show torque specs in their brochures. Does this really matter??






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 09-08-2002, 06:44 Post: 42139
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 4 cyl. vs. 3 cyl. diesel

I don't think it's much of a practical issue. It eventually does become an issue if engine work is required since 4-cylinder engines are more expensive to rebuild. But few compact owners are ever going to need a rebuild. I wish I could recall an explanation I heard about 3-cylinder diesel engines having some advantages over 4-cylinder ones. The explanation had something to do with firing and degree spacing.

Torque and HP can get to be pretty complex subjects. I think several long discussions are in the archives. Basically, HP and torque are closely related and can be calculated from each other at a given rpm. Torque basically is HP divided by RPM times a constant to get from HP to foot pounds through minutes. I think the formula is in the archives.

The formula would give torque from HP at the rpm speced for the HP rating. That rpm probably is the max HP point and probably isn't the max torque point. However, two points are pretty close in most diesel engines.

In practice it's a little tough to judge performance from HP or torque specs. Analyzing specs is a good way to learn about tractors and that has value in itself. However, my notion is that all the major manufacturers make good machines and the best way to find the best tractor is to try a few around dealers' yards. The best tractor for a person often is the one that feels best. Never the less, keep asking the technical questions here since most people here used this board to start learning about tractors. I imagine youíll get some useful responses, but talk to a few dealers as well.






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 09-08-2002, 10:23 Post: 42142
EdC
2002-09-08 00:00:00
Post: 42142
 4 cyl. vs. 3 cyl. diesel

I believe the unknown advantage mentioned that is related to firing sequence and degree spacing is that 3 cyl engines have a natural vibration reduction advantage (as do 6 cyl engines) over 4 or 8 cylinder engines and thus require less vibration dampening enhancements such as heavy flywheels and counter balances.






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 09-08-2002, 19:38 Post: 42153
jeff r



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 4 cyl. vs. 3 cyl. diesel

Let's look at it the dollars and cents point of view. A 3 cylinder engine is way cheaper to build than a 4 cylinder engine. One less piston, one less connecting rod, one less set of valves,shorter crankcase, less machining on the crank journals and engine block/heads, LESS material to buy, 3 injector set rather than 4. A manufacturer puts LESS money in manufacturing costs with a 3 cylinder than a 4. Personally I think internal cumbustion engines should come with an even numbers of cylinders. With a 4 cylinder you have a cylinder firing every 90 degree turn of the crank not 120 degrees as with 3 cylinder. I challenge the "smoothness" theory with odd numder cylinders. How many 3 and 5 and 7 cylinder cars you see on the roads today???? Makes one wonder doesn't it????






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 09-08-2002, 22:35 Post: 42159
DRankin

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 4 cyl. vs. 3 cyl. diesel

Audi used to make a 5 cylinder and for all I know maybe still does.
Three's and fives are the basic engines and I see the sixes, especially the V-6 as a "doubled" three and the same for the latest craze.... V-10's, which are just "doubled" five cylinder engines. Conversely, some years back, Pontiac made a slant four that was no more and no less than a half bank V-8. So I think the three and five cylinder technology is alive and well out there.
Note on Kubotaís: The B 7500 engine (21HP) is a three-cylinder version of the B 2710ís 4- cylinder (27 horse) power plant. The bore and stroke dimensions are identical.
The same relationship exists with the B2410ís 3 cylinder (24HP) and the B2910ís 4-cylinder (rated @30 HP), again, same bore and stroke numbers.
Also reading between the lines, the four cylinder models have uniformly higher top speeds for the same max RPM's, a bit more speed than you can account for by considering their slightly larger tires.
Translation: the three cylinder versions are geared a bit lower overall to compensate for their reduced horsepower and torque. So, not to worry, pick the HP range you need and trust that the tractor, engine and drive train are configured correctly to do the job.






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 09-09-2002, 00:03 Post: 42164
Peters

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 4 cyl. vs. 3 cyl. diesel

Dynamic balancing is natural for a 3 and 5 cylinder diesel engine. 4 and 6 for a gas engine.
There are a number of 5 cylinder diesels made as well as three cylinder.
Volvo also sells a 5 cylinder gas engine, but has counter balance shafts to enhance dynamic balance.






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 09-09-2002, 05:13 Post: 42167
jeff r



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 4 cyl. vs. 3 cyl. diesel

The reason guys, mfg's use the same pistons as the 3 to 4 cylinder counterpart is DOLLARS guys. WHY SHOULD A MFG make 2 different pistons between 3 and 4 cylinder engines? That's right he doesn't. Just because a small car companies like AUDI and Volvo make a 5 cylinder doesn't make them a good design. I stand by what I said. A 3 cylinder is far less expensive to manufacture than a 4 cylinder. Combined with the same piston size between 3 and 4 cylinder blocks and you have a very economical parts manufacturing process. IT's ALL ABOUT DOLLARS GUYS. FIgure out the dollars and cents equation and the rest is easy. Even numbered cylindered internal cumbustion engines manufacrured since 1940 out number odd numbered cylindered engines a billion to 1. How many people reading the posts on this site have an odd numbered cylinder car or truck? How many pieces of HEAVY diesel construction equipment have 3 and 5 cylinder diesel engines? What do farm tractors have? I rest my case.






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 09-09-2002, 07:06 Post: 42173
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 4 cyl. vs. 3 cyl. diesel

My sort of subject, but I'll add a voice of moderation for a change and say that maybe we should keep a balance of following our interests and helping Woz's tractor buying decision. I'm interested in specs and design issues, but I really do believe specs can get in the way of buying a tractor. To me, going through specs is a way to learn about tractors, and specs act sort of like a bookmarker for a person while waiting for the 'Ahh this is the one' experience.

Vibration damping is what I remember about 3 vs. 4-cylinder design comment I mentioned. I'm also certain that fewer cylinders does reduce manufacturing costs. There's a good chance that everything said here is true. How manufacturers saw off design vs. cost issues would be very complex and beyond me but I'm usually among the first to think that in recent years cost is dominant. However, my Ford 1710 has a 3-cyl diesel. I think that NH continued to use the 3-cyl engine when they first took over Ford but later used a 4-cyl engine in a redesigned 1710. If true, I wouldn't know how to explain that in terms of costs.

Mark: I'm not sure if your engine comparisons have the same displacements or not. There are various reasons for differences in speed other than gearing even in the same displacement engine. I heard a story about some NH models I think where an expensive and an economy version of about the same tractor were produced. The expensive version was rated for higher HP but the tractors used the same engine. The explanation was that the injector pump was turned up on the expensive model. The story didn't note if the rad also was larger to keep the engine cool.

Other than design, on a level the max load-load rpm adjustment on the throttle linkage is what determines top-speed. If itís turned up the tractor will go faster, but maybe thatís not so good for the engine.






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 09-09-2002, 08:36 Post: 42182
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 4 cyl. vs. 3 cyl. diesel

Hello Jeff;
I repeat. The 5 cylinder does not make sense for a gasoline engine. Audi and Volve make the engine for space considerations.
For a diesel this is different a number of companies make 5 cylinder diesels. Mercedes make a 5 cylinder for their cars. Volkswagon just made a V10, the highest power for a auto. Deere make 5 cylinders.
I am not sure why the balance is good in a diesel vs the gasoline engine. I would assume it has some thing to do with the point of ignition with in the cylinder.






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 09-09-2002, 08:51 Post: 42183
DRankin

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 4 cyl. vs. 3 cyl. diesel

Tom, I am getting the bore and stroke specs right out of the Kubota sales literature.






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Discussion Boards > Active Subjects > Messages as Posted > Kubota Review Forum

Thread 42136 Filter by Poster:
DRankin 5 | E. WOZ 2 | EdC 2 | Gregory Lee 1 | jeff r 2 | Mr Ed 1 | Peters 3 | TomG 5 | Tommy Smith 1 |




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