Fri Apr 16, 2004 10:14 am
I certainly agree with your view as well. I have some older equipment as well - a Porter Cable 1.5 hp router for an example. It is supposed to be equal to an 18amp router available now, but I can tell you for a fact the new one is absolute garbage -- got me a Craftsman.... what a hunk of junk compared to the PC.
The other thing that gets me, is that in the states, you have been able to get some remedial action on false claims such as power ratings, but us here well, we get to grin and keep paying for it!
It is another example of the old saying "Caveat Emptor". Seems that is becoming more common place now -- you have to be vigilant and understand that service and quality no longer are the by words for successful enterprises... alas, what a shame
Fri Apr 16, 2004 10:34 am
Your abilty to pull is Torque. Forget Horse-Power. HP is an abitrary number telling you nothing unless you know the torque.
Hp is the change Torque versus Time. HP = delta (torque)/time or the d(torque)/d(time) first derivitive.
I can have a 1 hp engine with 10,000 ft-lbs of Torque out pull a 10,000 HP engine with very small torque. Now see what I mean.
HP rating has nothing to due with the abilty to pull. It's all about Torque.
Fri Apr 16, 2004 11:01 am
True H.P. has everything to do with the ability to pull. It's a measure of how quickly it can be done... in other words how quickly torque can be applied. H.P. can be increased by increasing torque or reducing time in any combination.
There are engines that can exert enormous torque without turning at all... some steam engines. But when they are doing so they aren't developing any H.P. in the true sense, nor are they pulling anything. Horsepower is the ability to do work. Torque is merely one of the factors used in the calculation. Without time, it is meaningless.
Fri Apr 16, 2004 8:38 pm
Who Boy!! I think someone openned pandoras box. Man, alot of numbers, formulas and "stuff" Glad to see someone is on top of this!
Sat Apr 17, 2004 12:28 am
I believe torque and horsepower are understood by few people, and I'm one of them. I don't understand them from an engineer point of view, but feel my understanding is more "seat of pants". Something that hasn't been mentioned that I am constantly aware of the how different engines are built. Our little Cubs are a great example. Our engines are what is called an over square engine, meaning the stroke is longer than the bore. Oversquare engines develope more torque than standard engines like the engine in your auto. Your car was never intented or designed to pull heavy loads so the stroke is shorter than the bore giving a little better acceleration so your wife can get to Wally World a little quicker. Harley Davidson's are an oversquare engine and all harly riders have felt torque. Can you ever remember using a small gas engine mower and it flat out dies when it hits some heavy grass? Short stroke and no torque to keep it going. I'm trying to give some examples here for a little better understanding. A small block Corvette is a pretty fast and quick car. I think the cubic inch is 350 and it will develop something over 300 foot lbs of torque. My dodge diesel pickup is 360 cubic inch six cylinder and stock it developed 460 ft lb of torque. After I modified it quite a bit we put it on a dyno and the horsepower is now over 400 with over 800 ft lb of torque. Wow, my Frieghtliner has a big Cummins and it is 525 horsepower. So now my pickup can pull 80,000 lbs, right? Nope, even though the hp is close, the big Cummins has over 2,500 ft lps of torque. But I can sure give those small block vettes a run for their money! Sure gets interesting, doesn't it?
Sat Apr 17, 2004 7:45 am
The two trucks you compare can do very nearly the same work if
they are running at the RPM they have to to produce the 400 rated H.P., and are geared appropriately. Given the engine speed necessary to produce the power, what remains is the gearing to put the torque
to the drive axles. That big Cummins would be running too slow at 400 H.P., and the Dodge would be screaming, but they would compare closely in what they would pull.
This is the reason for transmissions.
Sat Apr 17, 2004 9:35 am
I can almost get my mind wraped around that. The big engine delivers peak power somewhere around 1400 rpm and the little one around 2800. Quite a difference there in rpm, like you say. The big engine has a 13 speed transmission and it is pretty easy to hold the rpm within 300 rpm of what you need at any road speed. This cannot be done with the little five speed. Without the gearing, the rpm has to make up the difference. It almost makes sense?
Sat Apr 17, 2004 3:01 pm
I recently was looking for info on the International Lo-boy 184 which as you probably know uses the same C60 engine used in the cub. Now keep in mind the 184's engine is a late cub engine which we all know had a little more hp due to increase in top rpm and some minor tweaks--but within reason it is the same engine as we usually discuss on cubs. I found a brochure on it on a Yahoo club for numbered series cubs and it listed the hp as 18.5. I puzzled over this for awhile before noticing the * by the hp number and reading the associated statement. I believe this tractor's hp must have been rated on engine hp instead of using the Nebraska pulling and pto tests used to rate our cubs. Since it is reasonably the same engine I'd guess our cub's engines produce about 16 to 18.5 hp.
If we increased our cubs max rpm to a lawnmowers speed of 3600 rpms, aside from probably blowing them up we'd produce much more engine hp.
Now I'm not going to say that there isn't some more creativeness in how the hp is numbered these days to make the sales literature look more impressive and perhaps back in the late 70's when that IH low-boy 184 was tested they didn't get that creative, but as George points out a lawnmower engine turning out 18+ hp is a powerful engine and might be just be as powerful as our cub engines.
I've looked at those Termite backhoe/loaders and their clones 4 or 5 years ago and noted many used 18 to 25 hp "lawnmower" engines and are capable of doing a lot of work. They usually also offer diesel engines too but this is not to increase the work they perform--just to increase durability. The "lawnmower" engines are a lower cost, less durable alternative of getting the same power.
I have the same kind of conversations from time to time. Like at work when I make a phone call to check on a part someone will hear me say something about my tractor and excitedly tell me they just bought one too. I'll ask "what did you get" and they'll say "A John Deere. It's got 25hp." I then inevitably find out they bought it from Home Depot. So, I have to refer to my Cub as a small, "farm tractor". Generally I try to avoid the hp question at all cost as then I have to explain they are rated differently etc.
I'm emailing Rudi a copy of that page in the 184 brochure
Sun Apr 18, 2004 6:27 pm
Actually HP is a better measure of speed than actual force. Hp measures the ability to move a given quantity in a given time. Torque is a measure of turning force. A modern Compact utility tractor with 12 PTO HP will not stand alongside a cub because the cub developes much more torque. Cub with less actual PTO HP, but stranger because the torque is the measurement of force.
A Farmall H is rated at about 27 PTO HP, try running a baler with a 27 PTO HP Utility Tractor!!
Wed Apr 21, 2004 6:17 am
Sorry George W but you are incorrect.
let me further simply this and show that the HP rating is irrelevent.
hp is the first derivitive of the torque curve versus RPM taking time into account.
If there is little change in torque versus RPM, then the HP rating is low. (ie a large long stroke slow speed diesel). the bottom nuber for torque can still be very high and just very little change versus RPM.
If there is a large change in torque versus RPM (very short stroke engine developing very high RPM's(i.e. racing go cart motors)), but the highest torque rating that is still very low will have a high HP rating greater than the large low speed diesels.
Can you see the difference now. Engineering school professors loved setting us students straight on this one when I was in school many eons ago.
Wed Apr 21, 2004 7:29 am
Jeez Randy, what school did you go to? George is exactly right.
Work is a force exerted through a distance (i.e. pounds x feet).
Power is work per unit of time (i.e. (pounds x feet) / minutes).
In rotational terms, you can simplify that torque is a force and revolutions are distance.
Work is torque x revolutions.
Power is (torque x revolutions) / time.
The first derrivative of torque vs engine speed (how steep the torque curve is) is a reflection of the efficiency of the engine vs. speed. If there is little change in torque vs. RPM, power increases more or less linearly with rpm. This is typical of small, short stroke engines.
Engines that develop the most power at low speeds do so because they have passed their torque peak and the additional speed is not able to cover the decreased torque.
Wed Apr 21, 2004 5:45 pm
- what is the formula to determine cubic inch displacement horsepower
I believe the above was the original question. Where's Bill Nye when you need him, eh? I'm sure one could do a search on the web and come up with "the" formula. I quoted one from memory. When applied to the C-60, comes up with about 10 HP. I believe I had got that formula from studying a millwright's hand book a few years ago. Whether or not one understands the true def. of torque, hp, and the applications of both, is not a requirement for owning and enjoying the SIMPLICITY of the cub.
Wed Apr 21, 2004 5:47 pm
As I think I said earlier....
I think I opened a very large
can of worms
It certainly got the discussion going though, and that is what this forum is all about....
Wed Apr 21, 2004 8:30 pm
Hey Rudi, nothing like pandoras box whaaa!!
Wed Apr 21, 2004 9:46 pm
- what is the formula to determine cubic inch displacement horsepower
I believe the above was the original question.
Going back to that question, the only "horsepower" rating I know of that can be calculated from basic engie dimensions is the old British "taxable horsepower."
I believe the calculation is:
((bore)^2 x cylinders) / 2.5
which comes up about 11 for a Cub.
Note that stroke isn't in the formula. That is one of the reasons european cars tended to have few cylinders and long strokes while the yankees were developing short stroke high speed engines.
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