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Old GTs Underpowered?

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The current issue of Popular Mechanics has a short article on lawn/garden tractors. Most of the current crop of GTs seem to have engines with larger hp ratings than comparable sized tractors of old. Are the older ones underpowered by todays standards? If so, in what ways are they limiting? Example; My 9020 Pow'r Max has a 19.5 hp engine and the tractor weighs about 1300 lbs compared to a Massey Ferguson Prestige with a 23 hp engine and weighing about 850 lbs.

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D-17_Dave
This kind of ?? has been asked before a few times. To me there are lots of answers. A few are nothing boosts sales like HP. This tractors more powerfull than the one next to it on the sales floor so whitch one you gonna buy?? Next is the way the tractors set up. Is it well engineered to make the most of it's given HP or is it designed cheap and easy to assemble? A common thing is to substitute extra HP for the imperfections of the quality and the way it was produced. There is a lot of diff. also between the output in HP and tourqe verses the older engines. While rated at the same rpm's, the older cast iron engines have a tremendous amount of inertia built into the tourqe rateing and don't give nearly as much when you load them down. The measure of HP comes in the amount of work that can be performed in a given time. These old equations are IMO very outdated in relation to the jobs these engines are performing. I'm sure I'm off on my explanation and someone will correct my definitions but I think I'm representing the results accurately. Truthfully it makes me sick to see them rate these newer mowers with these peramiters. If a newer tractor has a 25hp engine in it, then no matter what name is on the side of it, wiith all that extra power it should be able to do all the things my 620 can do and do them faster. RIGHT.

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HubbardRA
Hp = (Torque x RPM)/Conversion constant This formula is the same for all the engines. The older flat head engines are actually larger displacement than a comparable OHV engine like is being built not. In the newer engines, since they are smaller displacement, they don't make their peak torque till they get to fairly high rpm, but they do have the torque to make the required Hp at 3600 rpm. The older engines, because of their flathead design, made lots more torque at the lower rpms, but in many cases the torque was starting to drop off at 3600 rpm. In other words, as the rpm went down, the torque actually got higher within a specified rpm range, and normally at any rpm much less than 3600, they will have more power. What I am trying to say is that an old engine and a new engine of the same horsepower, both have it at 3600, but the power drops off much quicker on the newer OHV engines as the engine is loaded down to lower rpms. I think if we had plots of the Hp versus RPM for both types of engines, then it would be obvious why the newer engines seem less powerful. It has more to do with the shape of the Hp curve, than the actual value at 3600 rpm. You may find out that a flathead has 30 percent more power at 2000 rpm than an OHV engine. Since most of the time, we are not running the engines at WOT, then the old flatheads actually do produce more power relative to their ratings than the newer OHV types, when they are being operated at less than WOT. On most of the newer machines,there is only one attachment that is designed to use the full power of the engine. That is the mower deck. This is especially true with the sealed up mulching mower systems. Takes a lot of power to chop thru 5 - 6 times the amount of grass that you would have inside the mower with an open discharge chute. As I just said, the tractors appear so overpowered because the mower is the only part of the tractor that is designed to receive all of the engine power. Even the frame and aluminum trannys can't take the power of the engine, this is why they have gone to smaller wheels and tires(to reduce traction and prevent full power from being transferred to the ground) on the newer mowers, and don't offer the attachments that were offered on the older ones. As many say, " this machine not designed for ground engaging attachments".

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MadMike
I've always thought about it like this: Horsepower is cheap to make and the average buyer thinks more is better. Torque is expensive to make and the average buyer doesn't really understand what it is. Mike

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john-holcomb
These are great replies and all true. But trying to compair a 4 cylinder 12 hp cub with a 5 or 6 foot mower to a new 25hp box store tractor with a 48 inch moweris a hard thing to do. The thing to remember is the old cast engines will and have run for 40 or 50 years and the new throw aways are lucky to last 5 in heavy use. I like to think of it like they rate welders [Duty Cycle] an old copper welder may have a 65 or 75% while a new alu. wound machine may have the same amp rating but a duty cycle of 15% both will preform the same work but for how long?

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HubbardRA
I like the description John just gave. The specified Hp is the surge capability and is the same for both engines of a specific Hp rating, while the constant working capability on the older engines is much higher than the newer ones. Another real term that comes into play is "designed obsolescence". The newer engines are only designed to last a specified amount of time. The old engines were designed to last for very long periods, to be rebuilt, and go thru another use cycle. I think EPA has forced the issue onto the engine designers, that they don't want today's engines around ten years from now because the emissions requirements will be much stricter and all they want running at any time are newer, cleaner engines. In some states, they have even tried to pass laws that would ban any automobile over 10 years old from being driven on the highway. In fact, some of the proposed laws would have required that antique and classic automobiles would have to be modified to prevent the engines from being operable, otherwise they would have to be destroyed.

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bigcountry
quote:
Originally posted by HubbardRA
I like the description John just gave. The specified Hp is the surge capability and is the same for both engines of a specific Hp rating, while the constant working capability on the older engines is much higher than the newer ones. Another real term that comes into play is "designed obsolescence". The newer engines are only designed to last a specified amount of time. The old engines were designed to last for very long periods, to be rebuilt, and go thru another use cycle. I think EPA has forced the issue onto the engine designers, that they don't want today's engines around ten years from now because the emissions requirements will be much stricter and all they want running at any time are newer, cleaner engines. In some states, they have even tried to pass laws that would ban any automobile over 10 years old from being driven on the highway. In fact, some of the proposed laws would have required that antique and classic automobiles would have to be modified to prevent the engines from being operable, otherwise they would have to be destroyed.
My local dealer said that if the EPA was strict on enforcement, that he would have to bust up every cast iron block that came in for a rebuild, and have to repower it with a new low-emissions engine. He said, thankfully, they aren't very tight with inspections and all, just because there are too many dealers out there for them to keep an eye on.

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10HorseMan
Just put it this way, my B-110 with a 42" mower will cut a lot more grass that that new 20hp 44" cut cub cadet my grandpa got. It is not having a lot of power,it is how it is put to use. And the torque rating of the old engine is very good, it will get right down and lug it's way along. Bust up my block, No time soon.

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Simplicity314
Hey hubbard...another lesson that belongs here, I think, is the bore v. stroke ratios and their effects on performance, horse power and torque. I'd explain it, but you'll have to come along anyway to make all the corrections:o).

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HubbardRA
Jim, I don't think that the bore/stroke ratios have as much to do with the differences as the flat head versus OHV changes. OHV engines can produce much higher compression ratios, which yields higher horsepower in smaller engines. Then this needs to be related to the shape of the HP/rpm curves for the different engines. To adequately explain all of the details would take a small book.

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D-17_Dave
I'd say bore verses stroke has all the diff in the world with the tourqe ratios. It's a lot easier to pedal a bike with a longer pedal crank arm than a short one. The same goes for the ablility for the piston to turn a crankshaft. While the OHV engines produce a cleaner burn ratio and a more efficient and complete mixture burn, the older L-head engines with a longer stroke will develop considerably highr tourqe ratings than any of the newer engines.

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Roy
Regarding the bore/stroke ratio. Think small bore, long stroke, low revs, and lots of torque. A longer stroke generally has more torque than a short stroke. Tractor trailer diesel engines are a good example. Peak torque around 1,200 rpm. Pull forever at that speed. My 2 cents,

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swede
People, including myself, have a hard time with these numbers, but I have gotten better over the years. I have old hit and miss engines of various HP. People can't understand how something that weighs 300lbs and is that big, is only rated at 1.5 hp. It's the torque that counts here. These engines have about 16 ft/lb of torque at 500 rpm whereas a modern 1.5 hp engine would only have 2.2 ft/lb of torque at 3600 rpm. (Their respective RPM ratings) It's the same thing with autos. The new craze is to hop up a 4 cyl. car to 250-300 hp and go street racing. Well, there is no way I could swap one of those engines for the 6.0 in my chevy truck (300 hp) and pull my trailer full of toys to a show. Even if two GT engines were rated for the same RPM the older one will usually have more torque. They have more moving mass and longer stroke. Try reving up then idling a newer GT engine. The response is almost immediate, both up and down. The older ones take awhile to idle down - more mass. I was at our state fair and was looking at the Cub Cadets and saw one that had 25 hp with a 44 inch deck. I commented to the salesman on what a waste of an engine that was, but then backed off some because I realized they probably need that much to get the job done with these newer engines. I'm sure some of it has to do with the "I've got 25 hp under the hood" factor. Bottom line is, the older GT's hold their own just fine with 10-12 hp against the newer stuff.

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Conrad
Hi, I used to be a road runner for Cummins Engine Co. As such we had to explain the difference between Hp. and torque. Hp is how fast the load goes down the road, torque is what starts the load to move and keeps the load moving. In other words the faster you go the less torque you have. Also bore and stroke have everything to do with torque. You have three types of engine, square, under square and over square. Square means that the bore and stroke are the same and have good torque almost every where. Under square means that the bore is smaller than the stroke is long. (old flat head cast iron engines) This gives great lugging (Torque) power. The greater the load the more torque produced. (to a point) Over square means that the bore is larger than the stroke is long. This means that the engine has to run at high R.P.M. to get the power and has no lugging power. (Hence, the need for gear boxes)It has a flat torque curve. Hence, I like that hence) the high rpms needed by "vee" type engines. The vees were designed to conserve space, and generate speed. In summary, as rpm goes down due to load, torque increases on square and under square engines only. On over square engines the torque decreases to a stall point. I know this is long and very general but I hope yopu get the difference and the why. (Marketing.) Cconrad

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