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TFF

9020 versus 7119

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TFF

I picked up a great 9020 this week. It's been repowered, but runs like a champ. This got me thinking... Since I already have a 7119, why is the (original Onan?) 9020 so much more powerful than the 7119 (KT19)? I know horsepower is not the best judge on how much "work" a tractor can do...

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mtoney

I believe one reason is the Onan has a better torque rise than the Kohler. One of the reasons big green went with Onan in the 300 class was the torque rise and at the time the Kohler twins had some issues. Mike

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Brettw

Well, you say the 9020 has been repowered. The 7119 will be a 25-35 year old motor, so that could be a "new" 20 horsepower, and a very tired 19 horsepower. Now when you say "so much more powerful" how are you quantifying that? Equal tasks would help to determine the reality of the power difference. Same size decks cutting grass? Same size snow blowers? Hard to make the comparison when they don't have the same attachments to run. A one horsepower engine, geared correctly, could pull a train (all be it at a very, very, very slow crawl). The 9020 is a much bigger tractor, and should likely not be confused with horsepower. I recall as a kid, the local farmer got a 520(?) Case farm tractor. It was 52 horsepower and a BIG deal at the time. It is amazing what gearing will do and what can be accomplished with each and every horsepower.

Now, torque is a different thing. Someone will have to chime in about the two, horsepower and torque. I know just enough about the differences between the two to get in trouble.

Post like this are fun, because it brings out the discussions!

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GrincheyOne

Brett,

You are quite correct... My query got two interesting results.

www.epi-eng.com/piston_engine_technology/power_and_torque.htm

and

'>http://auto.howstuffworks.com/difference-between-torque-and-horsepower.htm

Don't remember much of this from High School Physics, but portions of the discussions seem to echo out of General Physics 101 at Temple U. one summer (lots of years ago)sm00

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PeppyDan

I believe the base reasons for the difference is in the displacement of the two engines. A Onan CCKB has 49.8 cubic inch displacement while a Kohler Magnum 20 (I think these have the same bore and stroke as the KT19) has 46.98 CID. As they say in the hot rod world....there is no replacement for displacement!

Dan

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huffy
quote:Originally posted by Brettw

Now, torque is a different thing. Someone will have to chime in about the two, horsepower and torque. I know just enough about the differences between the two to get in trouble.


id="quote">
id="quote">Here is how I have always understood it.Torque is an actual measure of force. Basically, it's how many pounds of rotational or "twisting" force the output shaft can produce. Horsepower, on the other hand, really isn't a measure of force; it's a calculation of how much "work" an engine can theoretically do in a minute. It's based on the mathematical formula of torque x rpms, divided by a constant (5 thousand something).So, say you have one engine that can produce 100 lbs of torque and runs at 50 rpms. Then you have another engine that produces only 50 lbs of torque, but runs at 100 rpms. They'll have the same "horsepower" rating. But, if equally geared the former engine will pull much heavier loads, etc. Thus, the first engine would be better for some tasks such as pulling a moldboard plow, tugging a loaded dump cart, etc. However, the latter engine may be better for things like mowing, snowblowing, etc, where you need the mower blades, auger, etc, to run at higher speeds. It is my understanding that the older engines ran at lower rpms than the new engines. So, a lot of the newer engines have a higher horsepower rating, even though they're really no "stronger," or in some cases not even as strong, as some of the older engines.

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TFF

Great discussion...thanks! My original comment came to mind after I had to move some of the 9020's attachments, which are so much heavier than my comparable 7119 attachments. 3 point hitch vs. sleeve hitch, etc. The torque/work/rpms relationship has always confused me, so great comments. One interesting note: the 9020's snowthrower turns so much easier than my 7119's - it's geared differently...but my goodness I can't move that thing by myself!

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midnightpumpkin
quote:Originally posted by TFF

Here's a picture

20141108_135008.jpg


id="quote">
id="quote">Nice looking tractor, you will really like that blade to plow snow. You said the 9020 has been repowered, the engine in the picture does not look like an Onan CCKB, what is the engine?John U

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mtoney

Its not so much a differance in RPM's. The older Onans turned at 3600 and so do new engines. But take a new engine just a few RPM off that 3600 and the torque/HP drops off way more than the older engines did. The range of RPM where the older engines made enough power to work was much more broad compared to new. That being said, you should never work an air cooled engine very hard below 3600rpm. They will overheat, very quickly on a hot day. Mike

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TFF

It was repowered with a Honda GX670, which has the lowest displacement when compared to the Kohler kt19 and Onan CCKB, yet the highest horsepower? Confusing. So the torque at 3600 rpms would be 35 for the Honda, 28.5 for the Onan and 27.7 for the Kohler... could this be correct?

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b52c130

TFF - what is missing is the "Volumetric Efficiency" of an older Flathead Engine verses a newer Overhead Valve Engine. The 'thru-put' of fuel/air mixture in an OHV engine is close to 20% higher than the "L-head" of the old flathead engines. And now the garden tractor world has caught up with the automotive world of the mid 50's. If you pump 20% more fuel/air mixture thru an engine at any given RPM, it will produce 20% more power. This is why "turbo" and "compressor" engines produce so much more power - more fuel/air mixture is being "pumped" thru the engine. I hope that this helps a little in the understanding of "old technology" verses "new technology" as far as engines go.

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b52c130

TFF - what is missing is the "Volumetric Efficiency" of an older Flathead Engine verses a newer Overhead Valve Engine. The 'thru-put' of fuel/air mixture in an OHV engine is close to 20% higher than the "L-head" of the old flathead engines. And now the garden tractor world has caught up with the automotive world of the mid 50's. If you pump 20% more fuel/air mixture thru an engine at any given RPM, it will produce 20% more power. This is why "turbo" and "compressor" engines produce so much more power - more fuel/air mixture is being "pumped" thru the engine. I hope that this helps a little in the understanding of "old technology" verses "new technology" as far as engines go.

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HubbardRA

It is more likely the shape of the torque curve for each engine, in other words the torque at each specific rpm. The reason I say this is that Horsepower = Torque * rpm / a conversion constant. So it is not so much how much torque you have at 3600 rpm, since all engines that have the same horsepower at 3600 rpm will also produce the same torque at 3600 rpm. The older flathead engines have a flatter torque curve than the newer engines. In other words the torque drops off less as the engine speed drops off on an older engine. This makes them much stronger at the lower speeds. The newer overhead valve engines make more power because of higher compression and more efficient fuel flow that they end up being much smaller at the same horsepower as the older engines, so as these engines slow down the power drops off much faster than the older larger engines. It is hard to do a direct comparison of two engines without having the actual performance curves of each engine.

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powerking_one

The increased power of an OHV/OHC engine over a flat head (L or T type) for a given displacement is more about the combustion chamber design and the ignition "flame" propagation. The most efficient type being a true "hemi" one; the spark plug centered over the piston,and ideally the head chamber being nearest to a hemispherical geometry. This way the forces of ignition/combustion are all directed straight down on the piston. On a flat head engine, the intake/combustion/exhaust flow have to take a right-angle "L" turn to/from the piston and valves; a significant loss in efficiency over the OHV/OHC.

Tom(PK)

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