Diesel vs gas

[MossRoad]

I've always been of the school that diesels pull better, are stronger, etc.... until I got to looking at this machine back in the early 90's. The numbers didn't add up, and the gas performed just as well as the larger diesel as far as output goes. Yes, it consumed a lot of fuel. Diesel cost more than gas at the time, but if you'd have gotten off-road diesel, it was pretty much even at the time. For me, the gas engine was a piece of cake to work on myself.

When I see people comparing gas engined tractors to diesel engined tractors, and then throwing in trucks, I like to look at the total cost of driving them both, and finding the break even point.

I found this calculator, where you can plug in the price of gas, gas MPG, diesel, diesel MPG, price per gallon of DEF, DEF MPG, the extra cost for the diesel engine option, and the miles it will take to break even. It was pretty interesting. I plugged in the numbers for my Suburban, and it was something like 450,000 miles before I'd break even.

Wish there was something like that for a tractor, but, since about no one sells a gas tractor, who cares? !! :laughing:

Gas vs Diesel – A Calculator and My Thoughts

 

[searcyfarms]

here is some hp/math for you, data from Nebraska Tractor Test 957 and 955 - closest i could find just right off 291 gas vs 310 diesel - the gas is smaller, used more fuel - both tested/rated engine speeds were 2300 rpm WOT, to produce the power of the diesel and get to a 5.0 gallon/hour fuel consumption you had to reduce the load on the gas engine by 50% - now what was the question............so to get the gasser to consume 5.0gal/hour you have to drop below 50hp, at 50 hp the diesel is only using 3.6+ so at 50hp i can assure you the gas engine is running more % of the WOT 2300 RPM and the diesel is purring much lower rpm as well as using less fuel - unfortunately NTT didn't use rpms on their graphs but i can tell you from old school math when the gas gauge said empty at noon it was out of HP and the diesel still had fuel and had plenty of HP to make it through the rest of the day ;-)



Type: 291 gas Torque Amplifier 2WD

PTO power (rated engine speed): 76.56 hp [57.1 kW]

PTO fuel use (engine speed): 6.3 gal/hour [23.8 l/hour]

PTO power (rated PTO speed): 71.8 hp [53.5 kW]

PTO fuel use (PTO speed): 5.8 gal/hour [22.0 l/hour]

Drawbar power (max): 65.67 hp [49.0 kW]

Drawbar fuel use (max): 6.3 gal/hour [23.8 l/hour]

Drawbar pull (max): 8,387 lbs [3804 kg]

then you have the diesel

Type: 310 diesel Torque Amplifier 2WD

PTO power (rated engine speed): 76.09 hp [56.7 kW]

PTO fuel use (engine speed): 5.0 gal/hour [18.9 l/hour]

PTO power (rated PTO speed): 71.84 hp [53.6 kW]

PTO fuel use (PTO speed): 4.7 gal/hour [17.8 l/hour]

Drawbar power (max): 67.46 hp [50.3 kW]

Drawbar fuel use (max): 5.0 gal/hour [18.9 l/hour]

Drawbar pull (max): 8,416 lbs [3817 kg]

Max pull gear: 3-Low-TA

 

[XSKIER]

Take two engines, gas and diesel, of the same displacement...say 6.0 liters each.

Say your target torque, ignoring HP for simplicity sake, is 300 Hp. The diesel can achieve this by only using 50% rated power and 2500 RPM. The gas can achieve this by having to use 90% rated power and 4500 RPM. Duty cycle is a generic term, but once you start calculating by engine load factors...you can see just what engine has to work harder to achieve the target torque for a given application.

That's great! Consider at 14.7 lbs of boost a 6.0L engine will be displacing 12.0L of Air. I wonder how your 6.0 diesel would run naturally aspirated? If Deere put the GAS 50hp Chinese motor that is in their gators in a compact tractor, I'd buy one in a second!

 

[Snobdds]

That's great! Consider at 14.7 lbs of boost a 6.0L engine will be displacing 12.0L of Air. I wonder how your 6.0 diesel would run naturally aspirated? If Deere put the GAS 50hp Chinese motor that is in their gators in a compact tractor, I'd buy one in a second!

Well naturally, the diesel application would only need 1/2 the displacement (3.0), with 14.7 lbs of boost to get the same rated HP. With again, far less fuel to do the same job.

The law of physics, is the law of physics...can't change those. Duty cycles or load factors, what ever you want to call it, always has the diesel with the advantage when all aspects of power are looked at.

 

[CincyFlyer]

25:1 compression? I doubt that more like 17:1.

As far as horsepower goes a gas engine of the same displacement will out perform a diesel. With tractors weight is not that critical so you slap a turbo on or just put in a larger engine.

The power curve of a diesel is also good for tractor work. If the engine gets loaded down and slows down there is still good torque at lower rpms where a gas engine falls on its face and will die.

Modern gasoline engines can have torque curves that shame a diesel's. It's just that that technology goes into Porsches, not Kubotas.

 

[MossRoad]

here is some hp/math for you, data from Nebraska Tractor Test 957 and 955 - closest i could find just right off 291 gas vs 310 diesel - the gas is smaller, used more fuel - both tested/rated engine speeds were 2300 rpm WOT, to produce the power of the diesel and get to a 5.0 gallon/hour fuel consumption you had to reduce the load on the gas engine by 50% - now what was the question............so to get the gasser to consume 5.0gal/hour you have to drop below 50hp, at 50 hp the diesel is only using 3.6+ so at 50hp i can assure you the gas engine is running more % of the WOT 2300 RPM and the diesel is purring much lower rpm as well as using less fuel - unfortunately NTT didn't use rpms on their graphs but i can tell you from old school math when the gas gauge said empty at noon it was out of HP and the diesel still had fuel and had plenty of HP to make it through the rest of the day ;-)



Type: 291 gas Torque Amplifier 2WD

PTO power (rated engine speed): 76.56 hp [57.1 kW]

PTO fuel use (engine speed): 6.3 gal/hour [23.8 l/hour]

PTO power (rated PTO speed): 71.8 hp [53.5 kW]

PTO fuel use (PTO speed): 5.8 gal/hour [22.0 l/hour]

Drawbar power (max): 65.67 hp [49.0 kW]

Drawbar fuel use (max): 6.3 gal/hour [23.8 l/hour]

Drawbar pull (max): 8,387 lbs [3804 kg]

then you have the diesel

Type: 310 diesel Torque Amplifier 2WD

PTO power (rated engine speed): 76.09 hp [56.7 kW]

PTO fuel use (engine speed): 5.0 gal/hour [18.9 l/hour]

PTO power (rated PTO speed): 71.84 hp [53.6 kW]

PTO fuel use (PTO speed): 4.7 gal/hour [17.8 l/hour]

Drawbar power (max): 67.46 hp [50.3 kW]

Drawbar fuel use (max): 5.0 gal/hour [18.9 l/hour]

Drawbar pull (max): 8,416 lbs [3817 kg]

Max pull gear: 3-Low-TA

Thanks! :thumbsup:

 

[buickanddeere]

I would go diesel any day of the week, i own 6 diesel engines and would not take a gasser in place of any of them - they have their place

Diesel engine痴 of what era doing what task ?

 

[buickanddeere]

Take two engines, gas and diesel, of the same displacement...say 6.0 liters each.

Say your target torque, ignoring HP for simplicity sake, is 300 Hp. The diesel can achieve this by only using 50% rated power and 2500 RPM. The gas can achieve this by having to use 90% rated power and 4500 RPM. Duty cycle is a generic term, but once you start calculating by engine load factors...you can see just what engine has to work harder to achieve the target torque for a given application.

Start out with both engines being the same rated HP or you are just comparing apples to oranges. Now for conversations sake compare a natural aspirated diesel vs a natural aspirated gas of the same displacement .
And what is the crime if the truck engine turns 4500rpm on a hill? It is not going to blowup or wear out any sooner . We are comparing light duty highway use vs HD applications such as marine propulsion or base load generator sets. Those are applications where engines operate at full load for months at a time and can easly rack up 6500+ hours a year.
My old 2003 pickup has 195,000 miles and the hourmeter is approx 6600hrs. The concerns regarding engine life have no merit . The body will be rusted off the frame before the engine fails.
In any case I can drop in a brand new long block cheaper than just a set of injectors and EGR repairs on a diesel .

 

[buickanddeere]

diesel, i don't have to run my engines near as hard to get my work done and listen to screaming gas engines slurping fuel - for instance - growing up drove a 706 gasser for one particular farmer...........big gas engine, filled it up twice a day - that same farmer i worked for drove the 856 diesel, he only filled up every morning - i don't think his 856 worked near as hard, my ears were ringing every night from listening to that 706 scream all day but it never failed me it was just loud n thirsty, so when my wife hollers at me i say, HUH, don't forget honey i have tractor ears!!!

I have no idea why some of you drag up stories of the 1960痴 when gassers had carbs, points and diesels had just a mechanical injection pump . When diesel cost about 2/3 hat of gas.
Take a look over at the calendar on the wall. Brace yourself for the shock Rip Van Winkle it is July 2018.
Can you think of any differences regarding 2018 gasoline and 2018 Diesel engines ?

 

[buickanddeere]

here is some hp/math for you, data from Nebraska Tractor Test 957 and 955 - closest i could find just right off 291 gas vs 310 diesel - the gas is smaller, used more fuel - both tested/rated engine speeds were 2300 rpm WOT, to produce the power of the diesel and get to a 5.0 gallon/hour fuel consumption you had to reduce the load on the gas engine by 50% - now what was the question............so to get the gasser to consume 5.0gal/hour you have to drop below 50hp, at 50 hp the diesel is only using 3.6+ so at 50hp i can assure you the gas engine is running more % of the WOT 2300 RPM and the diesel is purring much lower rpm as well as using less fuel - unfortunately NTT didn't use rpms on their graphs but i can tell you from old school math when the gas gauge said empty at noon it was out of HP and the diesel still had fuel and had plenty of HP to make it through the rest of the day ;-)



Type: 291 gas Torque Amplifier 2WD

PTO power (rated engine speed): 76.56 hp [57.1 kW]

PTO fuel use (engine speed): 6.3 gal/hour [23.8 l/hour]

PTO power (rated PTO speed): 71.8 hp [53.5 kW]

PTO fuel use (PTO speed): 5.8 gal/hour [22.0 l/hour]

Drawbar power (max): 65.67 hp [49.0 kW]

Drawbar fuel use (max): 6.3 gal/hour [23.8 l/hour]

Drawbar pull (max): 8,387 lbs [3804 kg]

then you have the diesel

Type: 310 diesel Torque Amplifier 2WD

PTO power (rated engine speed): 76.09 hp [56.7 kW]

PTO fuel use (engine speed): 5.0 gal/hour [18.9 l/hour]

PTO power (rated PTO speed): 71.84 hp [53.6 kW]

PTO fuel use (PTO speed): 4.7 gal/hour [17.8 l/hour]

Drawbar power (max): 67.46 hp [50.3 kW]

Drawbar fuel use (max): 5.0 gal/hour [18.9 l/hour]

Drawbar pull (max): 8,416 lbs [3817 kg]

Max pull gear: 3-Low-TA

That is a slanted comparison and you know it .
Compare both tractor engines at 100% power and compare both engines at 50%power . Your diesel at part load is now looking lousy with it’s HP per pound of fuel per hour vs the gas.
Now let’s get back to the reality of 2018 and light-media duty applications such as passenger vehicles , lawn/garden equipment, portable equipment , small construction equipment and off road recreational machines .
Due to the diesel costing as much or more than gasoline per gallon and Tier IV emissions . The diesel has been priced and strangled out of the light-medium duty market . If if was not for the fact that most of the rest of the world places luxury tax on gasoline to make it much more $$$ than diesel and does not have Tier IV emissions . The small Diesel engine would not exist and manufactures would stop building them .