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Easy, it’s all about the Onan. Massive cast iron flywheel with cooling fins. The yanmar just doesn’t have it. But, as they say, imho.
Torque is torque. Since it's a function of turning force over time and they are both rated at 18 HP, they should be about the same. Right out of the box, the 322 being 100 lbs heavier would have the advantage.

But I think Mr. "TempletonJDguy," is just stirring the pot looking for a lively discussion. If it's the numbers "Bolensman" is looking for he could easily look them up. Being they are both rated at 18 HP, the torque is likely to be very close.

IMHO :)
 
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I’m no aircraft mechanic. I think the yanmar is rated at 16. Mine is opinion only. To me the Onan has more power and pulling torque in the deep grass than my 332. I don’t have a 322 so can’t compare to that. Also been my experience the older motors with heavier flywheels out perform any newer motor rated at the same horsepower.
 

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I'll take the torque of the Yanmar diesel thanks. LOL................ I have a JD 318 Onan and the 332 diesel Yanmar beats it hands down in tall grass with a 50" deck, so unless my Onan is just beat to death. I mean it only starts on one cylinder then the second one fires.................. Who knows?
 

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Onan B43G: gas 18.2 PS (13.4 kW; 18.0 HP) at 3,600 rpm of horsepower and 43.0 N·m (4.4 kg·m, 31.7 ft·lb) of torque.
Source:
322 yanmar: 3TG66UJ 13.4 Kw (18hp) 4.2 kgM (30.3 ft/lb)

Source:
but its more than just absolute numbers. Power delivery at rpm is also a factor, not only in how it operates but how it “feels” when loading it down. Generally, a diesel makes more torque at lower rpms than a gas engine, which makes it feel more powerful. Whether or not that works for you depends on what you are using it for.
 

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It's easy to get off track with these 322/332's comparing gas to diesel. I don't think there is any argument about diesel being a tougher engine both in pulling power and durability. The OP was asking about 318's vs. 322's. So, unless you have both side by side on the same day doing exactly the same thing, both in the same condition, this conversation is nothing more than idle chatter.
 

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It's easy to get off track with these 322/332's comparing gas to diesel. I don't think there is any argument about diesel being a tougher engine both in pulling power and durability. The OP was asking about 318's vs. 322's. So, unless you have both side by side on the same day doing exactly the same thing, both in the same condition, this conversation is nothing more than idle chatter.
Sorry we got off topic. Don't kick us out. 🙏
 

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WOW ! I never expected such a response. Thanks to all the JD owners .It was nice torqueing to you.
We're just a bunch of old foggies with nothing better to do in the morning.
 

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Onan B43G: gas 18.2 PS (13.4 kW; 18.0 HP) at 3,600 rpm of horsepower and 43.0 N·m (4.4 kg·m, 31.7 ft·lb) of torque.
Source:
322 yanmar: 3TG66UJ 13.4 Kw (18hp) 4.2 kgM (30.3 ft/lb)

Source:
but its more than just absolute numbers. Power delivery at rpm is also a factor, not only in how it operates but how it “feels” when loading it down. Generally, a diesel makes more torque at lower rpms than a gas engine, which makes it feel more powerful. Whether or not that works for you depends on what you are using it for.
To Toumax's point, a factor is how the engine responds to the change in load, also the RPM range it makes torque. But aside from that, something else worthwhile...The Onan engine has the horsepower given at 3600RPM, which I doubt it is spinning that fast on most people's tractors.

It would be great to have the torque curves, but below the numbers we've already got. I plotted the hard knowns, and the estimated ranges. Since RPM, Horsepower, and Torque are related (Ft-lbs * RPM / 5252 = HP), we can at least look at the approximate HP/TQ values in the upper RPM range for the gassers. I included the full curves for the 332 direct from Yanmar simply because I have them. Use as a frame of reference for the diesel only, since that's not the question :)

The flywheel on the 318 is pretty huge, but it is also a huge air mover, which takes away some of its effectiveness as a flywheel. On the other hand, the 322 also has a huge flywheel without the need to move air. However, there is probably more rotating assembly inertia within the 3 cylinder, which also helps the flywheel effect. But the engine also has to run the accessory drive (cooling fan and water pump) which are parasitic losses that the 318 does not have. It might be a bit of a wash between the two, performance wise were there to be a good apples-apples comparison.

From what I can find, full load fuel consumption of the 318 is listed as 1.4-1.8 gallons per hour (duno what's realistic), the 322 is 1.4-1.5 gallons per hour (again I don't know, just what I have found on the forums), and the 332 is 0.8 gallons per hour (about right by my calculation).

Without knowing what the entire torque curves look like for the 318 and 322, everyone's guess is as good as anyone else's. I'd really love to know what the sales req would have had to say to a potential customer back then to try and upsell from the 318-322-332.

Rectangle Slope Plot Font Line
 

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Well, the OP specifically said he didn't want a physics lesson, but he got one. (We seldom listento such requests) Nevertheless, nice work, and it is appreciated. But I doubt Deere gave a rats behind what the torque ratings were back in the day. More like what fit and what was available. And as the auto companies, they would change things just to make them a little more attractive to the buyer. eg: water-cooled, diesel, etc. It's likely the 300 series tractor model numbers followed the advertised engine horsepower to some extent and the tractor was designed around the engine to a large extent. In other words, talking about torque in a garden tractor makes for a lively discussion but little else.

Now about that flywheel thing. It all depends on what you're trying to accomplish. Back in the day, one of the most common mods with hot rodders was shaving the flywheel to increase acceleration. Later, aluminum flywheels came along and likely still find their way into racers' engines. Sprint cars often ran no flywheel at all. Just a straight connection to an in-out box. All in the interest of fast acceleration. Aircraft engines have no flywheel other than the prop which make a very good one. But the accelleration is very slow mostly because even in the flat position they move a lot of air. I doubt it there is enough difference in the weight of an Onan flywheel vs a Kohler, or any other brand, to make an appreciable difference. The two being virtualy the same in design limits any advantage one migh have over the other. Newer "V" types withover-head valves are a different story and the older flat heads can't compete with. Which is why you seldome see them anymore.

Now, just the opposite is true on engines that need to lug heavy loads. The flywheels can become massive. But usually slow turning. Also, the design of an engine itself can change how the power is delivered. What's reffered to as an "over-square" engine had a bore larger than the stroke. It will accellerate much quicker than an equivilant engine size that is under-square. Or the stroke being larger than the bore. Most diesels are under-square. Most gasoline being over-square.

So, an engine producing higher torque can easily be a poorer application in many cases. All that torque usually equals slow accereration. So when you do dog that engine down, it takes that much longer to recover. If Deere or any other manufacturer cared about putting more torque in an engine, they would have looked at something totally different. And IMHO, there is not a hairs difference between any small engine in the size ranges we are talking about.

Those older engines are totally outclassed with the newer models available today in many ways. If your hanging your Onan hat on torque only, you're missing a lot. I'll take forty years of advanced technolgy over an ounce of torque anytime.

End of my physics lesson. :)
 

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The longer this thread goes on the more variables. So, I guess one can't simply say, "Onan's have more torque". Threads like this one are fun to read.
 
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