horsepower verses cubic inch

how is a ih 340 with 135 cubic inch rated at 40 horse,and a fafarmall H with 153 cubic inch rated at 23.i just feel Hs are underrated

I have a F340 and I feel it's over rated! :lol:

HP is torque * constant * RPM

A higher RPM engine just naturally shows a higher HP.

Many factors come into play with HP. Carb configuration, compression, RPM, and even the head configuration and the governor.

20 years of developement. Compare power outputs of today with that of 20 years ago.

(quoted from post at 11:32:08 03/05/14) how is a ih 340 with 135 cubic inch rated at 40 horse,and a fafarmall H with 153 cubic inch rated at 23.i just feel Hs are underrated

Click to expand...

Compare the rated RPMs and you will have your answer.

By the way, The Farmall H engine is actually 152 cubic inches, and is rated at 26 horsepower at the belt pulley or the PTO.

Nebraska Test Institute tested the 340 at 34.7 horse @ 2000 RPM. They tested the H at 26.7 horse @ 1650 RPM. The H ran approx 20% slower and made 23 % less horsepower. Not a big stretch as I see it. Where are you getting your numbers from?

I bet the H runs cooler/is more rugged.

Glenn F.

(quoted from post at 13:32:08 03/05/14) how is a ih 340 with 135 cubic inch rated at 40 horse,and a fafarmall H with 153 cubic inch rated at 23.i just feel Hs are underrated

Click to expand...

Same way it used to take 400+ ci V-8 in a car to get 300 Hp (with a few exceptions), and now they do it all the time with a 3.5 liter (approx. 210 ci)V-6... improved technology and RPM.
As with anything, there are exceptions, and one thing that causes problems with newer tractors is that "improved" technology in the added accessories.

It feels overpowered, because it's a high revving motor
(comparatively speaking), it has higher hp, because it revs
higher, but where it falls short is on lugging capacity. Torque is
what gets the work done. A 500 hp Ferrari will go fast, but it
wouldn't pull much of anything. Your modern 400 hp diesel 3/4
truck isn't nearly as fast, but because it has a lot of torque and
lugging power, it can tow mountains.

Not to get into a physics lesson here, but the statement that "torque is what gets the work done" isn't really true even though you see this repeated frequently. You can have all the torque in the world but it takes delivering it at some rate (in other words, motion) to get anything done. Think of a wrench on a stubborn bolt - if the bolt doesn't turn you have done no work even though you were applying torque. This is where the "power equals torque times speed" equation comes in - it is power that actually does work. Increasing the amount of torque you can deliver to the drive wheels (which is the only place it really matters) is as simple as downshifting but of course you will be moving slower. This is why engine power, not torque, determines how much work you can do in a given amount of time.

The reason that diesels feel stronger than a gas vehicle of equal power is that, because of the greater torque, the peak power is produced at a low engine speed that is usable in everyday driving. Most of us don't normally rev the gas engines in our vehicles to the 5000+ rpm it takes to deliver peak power so the potential goes largely unused.

Well stated. The Exotic engine in a Ferrari at 500 HP if coupled to a 4 to one reduction gear and clutched into a Quad Track would sure pull the hat off of Papa Smurf. Jim

> I bet the H runs cooler/is more rugged.

Not necessarily. Those engines ran slow because materials and manufacturing techniques were not adequate for them to reliably run faster.

More RPM, a little more cam, a little more compression and better head design. Like some said, the math result from raising the RPM has a significant effect

According to the Nebraska test results I looked at a 340 with a C135 test shows 32.3 horsepower for test C.
Test C on a gas H was 24.28 HP.
H engine tested at 5.9 compression.
C135 had 7.8 or 8.1 compression.
H tested with cast iron pistons, C135 not.
Put the same compression pistons in a H as a 135 with aluminum pistons and raise the RPM and see how much power difference there would be.

Getting way off topic here but just for curiosity I looked up the specs on a Ferrari V8 engine: 562 hp at 9000 rpm (!) and 398 ft-lb at 6000 rpm. With your mentioned 4:1 reduction this would give 562 hp at 2250 rpm and 1592 lb-ft at 1500 rpm (minus a little for gear losses). This is a lot more power and fully double the torque of the most powerful diesel pickup engines available today at the same transmission input speeds. Of course the life expectancy of the engine would be measured in minutes and it would burn a lot of fuel but that's why we have diesels to do this kind of work!

There are very few H's out there still making factory HP numbers.

When an H's engine is rebuilt, it is rebuilt with modern materials, modern tolerances. Overbore sleeves are installed for more cubes. The head has probably been planed multiple times over the years, increasing the compression ratio. Domed pistons are used, further increasing the compression ratio.

On a fresh rebuild, an H should be producing well into the 30's for HP.

Conversely, a 340 engine is about as tweaked out as you dare make it. There's nowhere to go to further increase performance. You're stuck with factory numbers.