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Jovee

Old Horsepower

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Jovee
I have heard bits of info on this subject here and there on horsepower ratings on older machines being rated differently than newer machines but never anything solid enough to go by. Is there any truth that the old power had been rated differently? It seems that so many of the old tractors were able to use 6-12hp engines for everything. The original owner of my Panzer said that 10hp motor would climb the side of a cliff while running implements and never have a problem. My uncle whos 5 yr old unit I fixed earlier this year, has a 20hp twin on it because it needed to climb his hill while the 68 Sears he had prior with the 8hp motor did it just fine. I know gearing and hi/los have much to do with some but is there a scientific reason for the average going from 6-12 to 15-27 hp over the years?8

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firefoxz1
First I believe the older engines were estimated Hp and also derated for longevity. Example and 10HP may have had 13 or more but only rated at 10Hp. Another reason they seem to work as hard is the cubic inches which gave them a straighter longer torque curve. Now on to the reason for the need for more HP: People want finer cut grass as in mulching which means you are no longer cutting your grass once every pass you are cutting it several times to make it smaller. I hope this helps because it is the way I see it.

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Morris
My recent thread on "what happened to the tractors" was sort of on this subject. I think a big difference is the use of vertical shaft engines as opposed to the horizontals. The verticals use a belt/pulley system, and that is an inefficient use of available power. The older horizontal shafts usually had a direct drive system (driveshaft) which reduced the amount of torque lost in the drivetrain. Example: My MTD has a strong running 12 horse engine. My Simplicity 700 has a 7 1/2. I had to pull a big Sunstar on 4 flat tires from the back yard to the front. MTD just sat there and dug holes. The Simplicity pulled it like it was nothing, and it weighed over 1000 lbs. But I have heard, too, that often those horsepower ratings were not truly accurate, and often were underestimated.

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thedaddycat
Old times rated the engines with old tech methods. Modern ratings of HP could easily be a calculated value based on fuel flow(which would then be converted into a HP rating based on the thermal value of the fuel). That is only a guess on my part, but the instrumants of today are certainly capable of measuring that accurately.

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BigSix
Isn't also to do with the switch from "brake" horsepower (bhp?) to SAE horsepower? I believe that in the sixties, the Society of Automotive Engineers changed the criteria for rating horsepower. I thought it had to do with the difference between measurements with no accessories (alt., waterpump, etc...) and measuring with. However, that wouldn't seem to affect small engines so much, as they don't have many "accessories." Al? A little help? LoL Peter

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dhardin
Another big factor in rating horse power is the amount of energy/power put to the wheels, the weight of the older tractors with driver can run 800 pounds and up. Todays nice riders with a driver might be as low as 500 pounds. I seldom have found of the new and old tractors i have played with. That its not the power i seen to be short on but sort on traction. I can get more done with my 10hp B110 than my 20hp Craftman.

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Jovee
Wouldn't they just factor hp rating straight from the engine first without weight and pulleys? Taking a 1969 10hp vertical, a 10hp horizontal with shaft drive and a 10hp horizontal sideways belt drive, wouldnt they all be 10hp? The shaft drive would obviously have the better connection but still runs most ptos by belt. Is a 2005 10hp engine more or less than the older counterparts? I dont think durability is there on the new stuff and maybe because of materials use in the construction would play a part. I would guess the older engines could be pushed more having heavier parts but why the change? I dont understand the fuel flow concept mentioned above at all.

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BLT
The formula for horspower hasn't changed. Getting more bang for your buck from better fuel usage has. In part you can thank the EPA for that. All water cooled engines should have one rating, gross, before any accessory HP such as fan, alternator and the like are deducted. Depending what you have for accessories will determine your net HP. All horspower is generally is accurate within 5% of the published rating. If you want guaranteed horespower, you deduct 5% of the published rating. In order to get maximum life out of an engine you design the power usage to about 50-65% of the published rating. This leaves extra power to get you 'over the hump' when needed and the egine is not at wide open throttle constantly. In my market I can have as many as 24 HP ratings depending on the vocation which also determines the warranty. Open pit mine trucks are about the hardest on fuel usage and engine life as their haul out of a pit might be as much as 45 min. All that time it is breathing fire and there is next to nothing for reserve horspower. Going back down might be only 15 min and little fuel consumption. So out of an hour you are 75% at full load engine power and 25% a figure a lot less. The air cooled engine market has everything built and their curves are net. They also note that equipment design should be at 85% of the published rating so you get some some engine life. Briggs used to test high volume machines to insure that the engine would get a resonable life and also keep their warranty costs down. They used to mow all the grass at a local airport every year as a form of quality control. And a car engine will not get anywhere the life as an industrial engine, because the to get like for like horsepower, you might have to spin a car engine at 5500 rpm versus 2000 rpm on an industrial and at that high speed you would simply wear out the parts.

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thedaddycat
I've said it before and I'll say it again now, I'll take my 40+ year old Simplicity(7 or 7.25 HP) up against any modern 20 HP Craftsman you can buy from Sears today(unmodified), at around a 3:1 HP disadvantage, and either drag it around the yard backwards all day long or just plain outright bury it any day of the week..... To date I have yet to see anyone take me up on the offer.....

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Guest
I'd pay admission to see that! :) BTW: I know someone who just paid a grand (yes $1000) for a 2-stage blower and plow blade for a 13hp 1990's Cub Cadet. Wonder how Kirk's 700/725's would do against that machine..... lol

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UCD
It all boils down to torque. Large bore long stroke vs. small bore short stroke. The older single cylinder Large bore long stroke engines produce more torque than the newer twin cylinder small bore short stroke engines. Long stroke = more torque, more torque = more pulling power. A single cylinder 16hp with 75 ftlbs. torque at 3600 rpm has more pulling power than a twin cylinder 25hp with 50 ftlbs. torque at 3600 rpm. (values used as example only)

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Alpha8D
All I know is I got a 1965 10hp and a spare 1966 12hp both briggs and I aint about to replace either one! I'll admit it's partly because they are simple enough I can work on them. Can't work on my own cars anymore so why not putter with a neat old tractor?

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HubbardRA
Horsepower = Torque x RPM / conversion factor The conversion factor is just to put everything in the same units. The older flathead engines were less efficient than the newer overhead valve engines. This means that they had larger bore and stroke than the newer engines. The older engines had a very broad, nearly flat torque curve over a broad range of engine speeds. The newer engines make the same horsepower on a dynamometer as the older engines at 3600 rpm. Because of the smaller bore and stroke, the newer engines make significantly less torque as lower rpms than the older counterpart. This is one thing that contributes to the differences. Another factor is that the older engines appear to be rated for "usable" horsepower. This means that the engine can be loaded and put out that horsepower all day long without problems. The newer engines appear to be rated at "peak" horsepower. This means that the engine can make and sustain that power for a short time but cannot maintain that power for long sustained perids. Many commercial items are rated at both "peak" and "usable, sustainable, or working" ratings, and both will be listed. Unfortunately the small engine companies do not explain the rating method, and in most cases it is difficult for an individual to obtain the performance curves for a particular engine so that the actual usable power can be determined.

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Kent
Good explanation, Rod. Another difference is that old engines also had heavy flywheels which helped maintain momentum and RPM when a load was placed on them. New engines do not. The flipside of this is that new engines, without the heavy flywheels (and with short strokes) will rev up much faster...

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Jovee
Thanks to everyone ^. I've been asked that many times and never knew the real answers. I used to jokingly say it was because Ralph Nader ruined it for everyone in the early 70s. I remember the major hp differences between my '73 and '74 Dodges[:0]. But I'm glad to be educated on this site :)

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HubbardRA
Elon, Not many people on this site who would even consider having one of those new Crapsmans. Pretty sure thing that nobody from this site will take Kirk up on that. I don't even have anything to put up against him, cause all of mine are Simp and ACs. I guess my Wards (Simp 700) with the 14 Hp Kohler wouldn't meet the requirements of his offer. LOL Don't think your modified twin cylinder "Beast" is what he is talking about either. I think it would be nice to take on one of those "Green things" that I see my neighbors riding. I can't get any of them to bite. I offered "hitch-to-hitch", offered to haul them both to a tractor pull for a grudge match, and offered a driveway cleaning contest with snow blades. Nobody will take me up on any of them. They just think I am crazy. Only comment I have ever gotten is a "mine mows faster than yours". I countered that one with, "I'd rather have quality, than quantity". He walked away and said no more. This guy mows his grass twice as often as I do, and when he is done it looks more like he used a bush hog than a finish mower. By-the-way, I could mow his yard faster than he does on technique alone. I watch all the circles he runs and how many times he goes into reverse trying to make perfectly sharp turns. Sometimes it looks like he spends more time running circles and shifting gears than he does actually mowing. Oh, well, we all know that "Simplicities and ACs Rule"!!! Can I get an Amen?

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BLT
Here is a typical air cooled engine power curve. It happens to be a Tecumseh 10HP RLM vertical shaft engine. This was the only one that was clear enough to post.

This curve tells me four things. 1. It has a useful operating range of 1800-3600 RPM 2. Out of the box, it will give me ten horsepower within 5% because there is only one torque curve. 3. There is about a 1200 RPM operating window. 3600 RPM down to 2400 RPM. 2400 RPM is about peak torque occurs and on a hard pull will drop off fast. What Maynard was reffering to was engines whose peak torque would drop off to say about 1800 RPM, hence more lugging before the engine pulls down. 4. The dashed line is the manufacturers recommended useable available horsepower to get a reasonable life before overhaul. If this had been a diesel engine curve there would also be a fuel comsumption curve. I haven't seen any carb contolled engines with them, but then my life has been with Diesel engines. [img]/club2/attach/blt/16v4000.jpg[/img] The above is 3000HP but the HP curve would tell me the same stuff. Horsepower is horsepower.

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Jovee
Thanks Bob - What we need is charts like that to compare a 40yr old engine's torque to a modern day engine's torque rating. The bore and stroke numbers of the older ones was more directed at my question as to why yesterdays 7hp engine could out perform or match a 20hp engine of today doing the same work be it horizontal, vertical or upside down. Chart comparison between the decades would be great. And so would motor mounts for that diesel to make the 310 run again. Rod - Amen!

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a7117puller
quote:
Originally posted by firefoxz1
.. Now on to the reason for the need for more HP: People want finer cut grass as in mulching which means you are no longer cutting your grass once every pass you are cutting it several times to make it smaller. I hope this helps because it is the way I see it.
They need the finer cut grass cause thin decks on other machines(which mow like crap), and the taller you want your grass, the more often you have to cut it...drop that deck and do a lil landscaping from time to time. (And chemicaly treated lawns eat thin metal mowerdecks)

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a7117puller
quote:
Originally posted by a7117puller
quote:
Originally posted by firefoxz1
.. Now on to the reason for the need for more HP: People want finer cut grass as in mulching which means you are no longer cutting your grass once every pass you are cutting it several times to make it smaller. I hope this helps because it is the way I see it.
They need the finer cut grass cause thin decks on other machines(which mow like crap), and the taller you want your grass, the more often you have to cut it...drop that deck and do a lil landscaping from time to time. (And chemicaly treated lawns eat thin metal mowerdecks) oh ya...AMEN!

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