Where's a CA get its power??

Higher RPM

CrestonM wrote: I'm kinda confused as to why speeding up an engine would give more power.

Simple answer:

Work, is force x distance. If you grab a 1 pound brick, and lift it one foot, you've performed one foot pound of work. If you lift the same brick up ten feet, you've done ten foot-pounds of work.

Power is work x time.

Let's say you make the first lift in one minute. That's one foot-pound per minute. Let's say you do that same lift ten times in one minute, that's ten foot pounds per minute.

Now let's say you lift the brick ten feet in one minute... that's ten foot pounds per minute. Now let's say you do it TEN times in one minute, that's a hundred foot-pounds per minute.


Now let's say that you have a B engine, with a hoisting drum on it that's exactly ONE FOOT in circumference. That's 12" / 3.14 = 3.821" diameter, and you've got a rope on it, to a pulley, and the engine was governed at 1500rpm. In one minute, that means it could lift a weight 1500 feet. Let's say the weight is 70 pounds... that means you're lifting 70 lbs 1500 feet, in one minute. 70 x 1500 = 105000 foot pounds of torque, per minute. Divide that by 5250 (a constant, for converting foot-pounds per minute, into horsepower) and you get 20hp.

Now, speed the engine up to 1650, and the result is 70 x 1650 = 115500 foot-pounds per minute, or 22hp.

Let's say that along with the raising of engine speed, there's also a compression increase, and there's better fuel available now (post-war), so a little more ignition advance, and a little better airflow overall, and now it can manage to pull an 83lb weight up the 1650' mineshaft in one minute... that's 83x1650 = 136950 ft-lbs/min, divide by 5250, and you have 26hp.

If you got crazy and wound that engine up to twice the speed, and IF it didn't come unglued, AND it could still pull the same 83lb weight, you'd have twice the horsepower on-tap.

The question is... WILL it stay together, and WILL it stay cool, and if so, for HOW LONG?

Now, this is totally ENGINE BRAKE HORSEPOWER... when you put that engine in a driveline of a machine, there's friction losses, and traction and driveline limitations. A tractor that has very little ballast for it's driven wheels, will generate very little drawbar horsepower REGARDLESS of the engine driving the wheels. Likewise, if there's lots of parasitic loads (like a big alternator, hydraulic pumps for power steering, etc., and lots of gears spinning in the transmission), you'll lose lots of power to that, so not as much available at the wheels OR at the belt pulley and PTO.

Does that clarify?

DaveKamp,
I learned something new today.  High school physics class makes sense now. 

John

Lester Larsen's book on tractor testing "Farm Tractors 1950-1975" says in the text, "The new Allis-Chalmers CA tractor was similar to its Model B but developed more power, because of a higher compression ratio and increased engine rpm."

I see that the tractor test data showed the CA also got better fuel economy, 10.29 hp-hr/gal vs 9.86 for the B tested that same year.

Dave Kemps horsepower physics explanation is very good.

In the real world an engine usually doesn't have constant torque with speed. It has a peak and the drops off at higher speeds because the manifolds, carburetor, and air cleaner air flow friction limit fuel ingestion at higher speeds and likely the carburetor tends to go lean at high air flows and then there is more mechanical friction loss at higher speeds, mostly pistons and rings and rod and main bearings. In automotive engines the torgue peaks at a lower speed than horsepower, but the makers advertise the peaks of the torque and the horsepower curves, even though often the horsepower curve peaks well above the normal engine operating speed range. That's specmanship. The beauty of Nebraska Tractor test data is that the horsepower is measured at working speeds and loads. The detailed data shows horsepower under many different operating conditions.

According to Nebraska Tractor test 439 in 1950 the B had a compression ratio of 5.75:1. http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1144&
context=tractormuseumlit

According to the test 453 the same year the CA had a compression ratio of 6.25:1 and the same sized intake and exhaust valves. http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1157&context=tractormuseumlit

Gerald J.

I have a B and I got a Ca gov spring   decided not to put it on just give more rpm .If you turn 1650 instead of 1400 and run the same ground speed the 1650 will be stronger because the ratio will be higher.More engine turns to the wheels one. Pretty simple . Speed up a B and you just get more RPMs and faster ground speed.

You will get some more power running the B engine faster, but not as much as running it faster and adding the taller pistons. You can gain more if the B was dual fuel because it came with lower compression ratio for distillate fuel. Books say there were two compression ratio options for the B and C for the different fuels.

Compression ratio has two effects, one is a bigger bang pressure after ignition with a higher compression ratio and the other is the amount of expansion used from that explosion. A diesel tends to have greater output for a given amount of fuel because of the high compression needed for compression ignition also allows for greater expansion. In a steam engine efficiency is increased by closing the intake valve early in the stroke and getting more expansion from the steam. That's also true in Prius gas engines. Their valves are set up to have a 15:1 or so expansion ratio with a 9 or 10:1 effective compression ratio. That makes for greater engine efficiency. Too high a compression ratio leads to pinging in a gas engine and that hurts engine efficiency. It also leads to a high combustion temperature and that causes greater nitrous oxide emissions.

Gerald J.


Edited by Gerald J. - 21 Jan 2016 at 2:32pm

Dick L wrote: The B has a taller final drive gear which would take away fuel usage under similar loads. The heads and firing chambers are exactly the same as close to exact you can get with a casting. I have opened up these engines where the 3 3/8" piston did not come flush with the top of the sleeves. The only way the test data could show a higher compression would be to compare the shorter piston in the B and the taller piston in the CA. I loved my CA's for plowing with the snap coupler plow but the data used to sell the tractors with higher HP and compression was smoke and mirrors. In saying so I am not downing the tractor one bit.  It was a big improvement over the C.   With the crankshaft having the same stroke and the heads being the same you are left with different pistons to change compression.  I never opened up a newer B of the years the CA's were built to know for sure  what piston the B was shipped with. I still have about a dozen heads from these engines from the older B's to the CA's and your welcome to come and measure them at any time.  The first thing I do to the heads when rebuilding them is to remove material to increase the compression with this cutter.

I always wondered about that Dick. Just out of curiosity, how much can you take off a B C CA head to bump compression? I know nearly 20 years ago I should have had new seats installed but didn't have the funds back then. Kinda got the itch to redo it right.

Edited by Dick L - 21 Jan 2016 at 5:33pm

 If you tell them to cut .200 off and somebody has already milled the head once, you could have a boat anchor that will still have to be paid for.
 I would guess, if you have 90+ in each cylinder, it ain't a K engine anymore.

CrestonM wrote: So I can take my head to a machine shop and have them take .200 off the head? If they mess up, I have another bare head from a B. Charlie...what defines a good compression check? Thanks

CrestonM wrote: It has 80 lbs give or take a few pounds.  How do I tell if it's already been milled?

When planing a head you may never know what has been done to it in the past. I've only ever had one head that was NOS and known to be a casting that had never been touched. I did the same a DickL and sawed through one to see what could be done. I determined the the spark plug holes were the key; just leave a minor amount of material at the large bore of the spark plug hole to be sure you can install the plugs without interfence.

PaulB wrote: I determined the the spark plug holes were the key; just leave a minor amount of material at the large bore of the spark plug hole to be sure you can install the plugs without interfence.

Dick and Norm both touched on the transmission, thought I would bring it to light just a little.
   Only considering low gear, since that is where the most pull is attained, although at a lower speed, the B has a 2.5 mile per hour road speed. The CA has a 2.0 mile per hour road speed.
  Now, considering the fact that the CA has a higher engine rpm, something has been changed, which could be the actual low gear in the transmission or a combination of the transmission low gear and the output gears in the finals. This should equate to the better pulling power that many have described.
   From experience while looking for an exact tooth count on a final gear for Hubnut, I figured out that there are several different bull gear combinations, so some of them might be used to attain this "added horsepower". However, since an overall road speed increase is also attained, and an extra gear, I would guess most of the changes that made a serious difference would be found in the CA transmission.
   As far as decking a head on a B to up the compression ratio, I would be really hesitant to do this on an engine that was also not getting the bottom end done at the same time. If the engine has sufficient wear to need the top end done, adding the additional compression to a weakened bottom end might bring about results that aren't what you weren't hoping for. Just my 2 cents.
   David from jax