Head Banger

Wed Apr 14, 2004 8:23 am

K, we all know the difference between Devloped HP and Drawbar HP correct :idea: :?:

Soooo, :roll: for those of us who haven't got a clue as to what kind of horsepower the C-60 Engine actually developes :? - what is the formula to determine cubic inch displacement :arrow: horsepower :?:

Cars are defined as having so many CI's with so much horsepower. I am kind of curious as to what that equivalent would be for the C-60 :?: This has come up in a number of discussions of late, and it would be nice to have the answer.....

Wed Apr 14, 2004 9:04 am

Rudi,

R.P.M. plays a big part in the equation. A C-60 at 4000 R.P.M. would probably put out about 40 H.P. (that's just a guess). :?:

It would be more useful to think in terms of cubic inches/minute as related to H.P.

In the case of automobile economy, the useful number for fuel consumption is cubic inches/mile. Larger engines usually are geared to turn slower.

Wed Apr 14, 2004 9:49 am

Yikes, what a can of worms! There is no formula to determine horsepower when looking at engine size. Valve timing, compression, combustion chamber design, ignition timing, fuel type and delivery, climatic conditions - just the tip of the iceburg.

Horsepower is a linear measurement of ability to pull a load over time, but engines and motors produce rotary motion. Therefore, horsepower rating for engines is a calculation of torque and rotation over time.

Horsepower is an arbitrary unit of measurement to begin with. It has been forced to relate to modern units of measurement - but it was originally developed to determine how much coal a horse could pull out of a mine shaft. Just as two horses will pull different amounts of coal, 2 engines (like a new one versus a worn one) can produce very different power results.

Wed Apr 14, 2004 11:21 am

Yeah, what Lurker said. Whew!!
Anyhow, I believe the following formula would or could apply to a multiple cylinder "small" engine. I don't remember the exact qualifications though.

bore2 x #of cylinders
--------------------------------
2.5

HR

Wed Apr 14, 2004 11:53 am

HP = (mep) ( L x a x n ) / K

Where: mep = mean effective pressure, lb/in squared. (Compression)
L = Stroke, ft
a = Total piston area, inches squared.
n = number of cycles completed per minute, RPM
K = 33,000

As george has said, HP is directly related to RPM. The horsepower is a linear progression based on RPM - you could plot HP vs RPM and it would be straight line (theoretically a stright line - compression changes with RPM and would curve the line with higher rpm - that's another subject)

Hope this helps.

Oscar

Wed Apr 14, 2004 2:00 pm

Well, I guess I can bang me head some more!

Wow, the knowledge that is out there. Way beyond my ken.

I guess what I was referring to is kind of like a VW engine. 1200 cc.s or 1.2 litre engine would produce about 45 hp or so they say.

A C-60 is about the same size I guess, but would never run up to 4000 rpm, course not too many people pop a bug at 4 grand either....

I was just trying to get a rough handle on it, so as when discussions come up like -

"gee, I got me a 20hp Craftsman, it should have more guts than your 10hp Cub -- ". It gets kind of difficult explaining the concept of drawbar horsepower to those not familiar.

Maybe we can do it this way. Top rpm on a Cub is 1800, but I won't run Ellie that high, more like 15-1600 max. So at 1600 rpm in first gear with the 193 plow on the end, what would the horsepower rating be --- roughly ----

the math is beyond me guys!

Wed Apr 14, 2004 2:10 pm

Rudi wrote:.

Maybe we can do it this way. Top rpm on a Cub is 1800, but I won't run Ellie that high, more like 15-1600 max. So at 1600 rpm in first gear with the 193 plow on the end, what would the horsepower rating be --- roughly ----

the math is beyond me guys!


And the answer is:......adequate! :wink:

Wed Apr 14, 2004 3:30 pm

Engine hp rating is a Madison Avenue gimmick. There's a lot of friction in the drive train that eats horsepower. The only power rating that matters is where the rubber meets the road (or impliment meets the mud).

There's plenty of old Cubs still going strong. Find out from your Craftsman fan how he expects to keep his machine going for 50 years.

Wed Apr 14, 2004 5:09 pm

K:

Message got and understood :idea: No need to compare because it is immaterial and like comparing apples to grapenuts :roll:

What you all say is true. My Craftsman is about 15 years old thereabouts, and it is almost done. Will never last 25 years let alone 50.

Ellie does what I need her to do and does it easily, so nuff said!

I guess I can go take a couple of Tylenol now huh :?: :oops: :roll: :wink: :lol:

Wed Apr 14, 2004 7:43 pm

Why not have a good old fasion tractor pull? Hook the Crafstman to the back of the Cub and see what the results are.

Wed Apr 14, 2004 8:11 pm

Hi All
I thought the very same thing as chess, but didn't post it, because of all those technical posts. I have limited seat time on my cub, but wouldn't the cub be pulling that craftsman around like a landscape rake ? especially if the cub had bar tires on it ? Paul K. in N.H.

Wed Apr 14, 2004 8:21 pm

Sears Lawn Tractors are Higher Speed(3600 RPM??), Higher Horsepower and Lower Torque machines than compared to Cubs. Cubs are Low Speed(1800 Rpm), and to my understanding around 13 Horsepower at the engine and Higher Torque machines designed to work and pull rated loads all day long and not Bog down as opposed to a Sears lawn tractors where they will stall alot quicker trying to work as hard as a Cub although the Horsepower rating is higher. The Key to the ratings on Commercial Lawn Tractors is that their Horsepower rating is at their maximum developed horsepower the engine can deliver and not self destruct. Operating the lawn tractor at this rating would probably result in a season or two of use from the engine before repairs are necessary. The Cubs ratings for Horsepower, or for that matter Antique Tractors in general, were more conservative and precautionary where the Cub could be expected to deliver at its rated Horsepower throughout its normal life.

Wed Apr 14, 2004 8:35 pm

John:

Yup, agree on all that, and I guess that in a nutshell boils down what I was trying to understand in a way that I could explain it to those who have GT's and know diddly about a drawbar hp.

Developed horsepower is a term/rating that really does not indicate much at all, and can be quite confusing. I know I certainly was for the longest time. In fact if I am not mistaken Campbell Hausfield, Coleman and a couple others were involved in litigation over that very term on their compressors. I imagine the same terminology/definition applies to B&S and Tecumseh engines as well.

As Chess and Paul said, the Cub can pull those GT's around probably in pairs and not break into a sweat...

Thu Apr 15, 2004 9:38 am

One thing to remember is that the lawn tractors are single 'A' belt driven machines.

The belt drive loses about 40% of the transmitted horsepower thru slippage, heat, & vibration. I used to have a direct drive "Power King" with a belt driven deck. It had a 14 hp single cylinder Kohler engine - it would cut circles around our 23 hp twin cylinder Craftsman; but, my wife didn't like riding the "Power King". So I gave up some efficency so my wife could do some mowing. A good trade I think :D

Oscar

Fri Apr 16, 2004 9:14 am

Rudi wrote:John:



Developed horsepower is a term/rating that really does not indicate much at all, and can be quite confusing. I know I certainly was for the longest time. In fact if I am not mistaken Campbell Hausfield, Coleman and a couple others were involved in litigation over that very term on their compressors. I imagine the same terminology/definition applies to B&S and Tecumseh engines as well.



Yes, you are correct Rudi and this makes it bad for the indivual that just doesn't know better. For an electric motor to be rated for hp, it is tested at running rpm to see how many amps it is using. The sellers like Sears and Campbell Hausfield decided to use the amp reading at peak startup to make their motors look powerful. I have old 1 hp motors that are stronger than the new 5 hp models. I have one old five hp motor that must weigh 150 lps, compare that to one of the dinky 5 hp motors they stick on an air compressor now. I hope they get burned for their decption!
Michael