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Discussion Starter #1 (Edited)
I was sitting around bored this morning and started to think about engines and power.

Anyway I took some of the more common engines found on Gravely tractors and made a spreadsheet. Then I added some data like calculated compression in PSI. Compression ratio * 14.7 = PSI

Someone might find it entertaining. It certainly confirms certain allegations and debunks others.



What I find interesting is the lowly CCKA data when compared to other engines.

The unexpected result of this data is the number of answers and questions it raises. It certainly has given me something to think about.
 

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Gravely Model L Guy
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Nice!
 

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Gravely Model L Guy
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You need to get the Gravely made engines on there!
 

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Discussion Starter #4 (Edited)
In reviewing this some more I need to add a few more engines and a little more data.

I suppose I should add some Kawasaki and Honda engines. Maybe a Robin too.
 

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Discussion Starter #5 (Edited)
You need to get the Gravely made engines on there!
I know that the Gravely engine is 3.25 x 3.5 (29 CID) but cannot find the compression ratio.

Don't read too much into this data. Many things can affect the amount of power generated by an engine. Exhaust backpressure and valve timing are just two.
 

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Very interesting data.

How do the Kohler K engines run with No/Available compression??






Just kidding!!!
Somebody must have the data!!

This type info, like the Nebraska Tractor tests is under used data.
 

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Discussion Starter #7
I think that the reason that there is no compression ratio data for the K series is due to the different heads that are used on those engines over the years. Brian Miller has a write up regarding the various heads used by Kohler.

http://gardentractorpullingtips.com/cylhead.htm
 

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Gravely bug bit.
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I know that the Gravely engine is 3.25 x 3.5 (29 CID) but cannot find the compression ratio.

Don't read too much into this data. Many things can affect the amount of power generated by an engine. Exhaust backpressure and valve timing are just two.
The most telling is that while the B48M in your example is 48 CuIn for 18 HP and the M20S is 47 for 20 HP, don't forget the B48M GA019 version that put out over 19 HP. Kohler went for HP while Onan went for torque.
 

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Discussion Starter #9
The most telling is that while the B48M in your example is 48 CuIn for 18 HP and the M20S is 47 for 20 HP, don't forget the B48M GA019 version that put out over 19 HP. Kohler went for HP while Onan went for torque.
There are other things that pop out as well. They are:

Just by looking at the data, the CCKA should put out more HP that the B48. I know it doesn't but it is interesting nonetheless.

The other fact that emerges is how much compression contributes to HP. The Briggs has a relatively small displacement but high compression.

Comparing the Vanguard 35 to the Onan P224 is another interesting exercise.

- The P224 has a larger piston but shorter stroke.

- The Briggs has more compression which pushes the developed HP higher.

Based strictly on the numbers and if the compression were equal, I would expect the Briggs 35 to have more torque than the Onan 24.
 

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Gravely Model L Guy
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I thought the K-series Kholers had a compression release is that why its N/A?
 

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I thought the K-series Kholers had a compression release is that why its N/A?
Compression ratios are calculated by measuring volume before and after moving the piston from the bottom of the stroke to the top of the stroke. If at the bottom your cylinder, gasket, & head has 100 CuIn of volume and at the top has 10 CuIn of volume, you have a 10:1 compression engine.
 

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Discussion Starter #12
I thought the K-series Kohlers had a compression release is that why its N/A?
The reason that the compression ratio is NA is because I cannot find it in any Kohler document.
 

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Discussion Starter #13
Added a couple of engines.

 

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Discussion Starter #14
The latest data.


 

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Discussion Starter #15 (Edited)
If anyone wants to download the spreadsheet, it is HERE

For those considering raising the compression of an engine, from what I have gleaned from a variety of data sources, the amount of horsepower increase resulting from a 1 point rise in compression ratio is about 4%.

Assuming the best case where a K301 starts with a 6.6:1 CR, raising the CR to 9.0:1 will net about 13 hp, a approximate 10% increase. It will also raise efficiency of the engine as well place additional stress on the engine. Sorry, there is no free lunch.

Here is a handy calculator.

http://www.bgsoflex.com/crchange.html

Other fun calculators:

HP calculator - Enter displacement and CR and get the expected HP (not entirely accurate but fun)

http://www.bgsoflex.com/roughhp.html

http://www.bgsoflex.com/auto.html
 

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Discussion Starter #16
For those that are interested in the P224 that was used on the 24G, here is a torque and horsepower and fuel consumption curve. Gasoline weighs 6 lbs per gallon.

 

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Discussion Starter #17
Let see if I can figure this P224 fuel consumption right.

Gas weighs 6 lbs per gallon

.70 lbs per hp per hour.

A 19hp load would mean the following:

19*.7 = 13.3 lbs
13.3/6 = 2.2 gallons per hour
5 gallons would last 2.2 hours

A 16 hp load would be:

16*.70 = 11.2 lbs per hour

11.2/6 = 1.86 gallons per hour
5 gallons would last 2.8 hours.

I think it is safe to say that a tank of gas (5 gallons) should last between 2 and 3 hours.
 

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From now on I only mow at 2450 rpm!!

The numbers sound right, I get two - 1.5 hour mowings' per fill-up. After two mowings she is running on fumes.


To determine if any engine is efficient, I compare them to the John Deere 820, which can produce 18 hp-hrs/gallon of diesel fuel. That is the best performance I have found.

So this one is about 9.6, not bad for a gas engine.

Some gas engines only give 2-3 hp-hr/gallon of gasoline!!

I mow a LOT of grass on a little gas!!
 

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Discussion Starter #19
From now on I only mow at 2450 rpm!!


To determine if any engine is efficient, I compare them to the John Deere 820, which can produce 18 hp-hrs/gallon of diesel fuel.
That is just plain cheating.

I you really want to see a diesel suck up the fuel, bypass the emission controls.
 

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Gravely 408 Authority
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Nice! How about adding the K181 engine used in the L-8 and 408?
 
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