Fuel efficiency question

[Drysleeves]

3 hours ago, Eason said:

I don't put much faith in Nebraska test. Look at the test for a 4020 and a 856. The test show a 4020 will out pull a 856. We all know the truth on that one!

I know two guys who had an 806 and a 4320. Both told me their tractors would do the same amount of work but the 806 would use less fuel.

Also know two other guys who had 560 Diesels and both of them told me their 560's made them so much money they could afford to buy a John Deere. The grandson of one of those men still has his grandpa's 560 Diesel and it's restored.

[Diesel Doctor]

On 8/1/2026 at 11:02 AM, Jacka said:

This question is for the true engine builders gurus.I am far from that.But running my David Brown today with its Alamo Boom mower gives you time to think.What makes one engine so much more fuel efficient than the next one? Is it head design,the way fuel is delivered, something about larger bore and shorter stroke or vice versa? Is it fly wheel size or weight? Why do different manufacturers have or used to have vast differences in fuel usage.I know my David Brown is as efficient as a tractor as they come.Its 65 hp or so.Plus it seems like the English or German tractors were more efficient back in the day.I know the Deutz owners always raved about them.

Yes, to all?

It is very complicated and some get it right and others don't.

Unsure if some is luck?

Ask an engineer!

[Injpumped]

The real question is if it's under light load, part load, or full load, that will dictate the fuel use the most on a diesel. The diesel will use very little under very light loads, like hay raking. A gas tractor of similar hp and light loads will use more fuel than a similar size diesel because a gas engine needs to maintain a fairly rich air/fuel ratio to avoid melting it down. A diesel engine only gets enough fuel to make the hp you demand of it, up to it's full load, and beyond lol!

[Gearclash]

A gasoline engine also has more pumping losses at part throttle; it is always expending power fighting the pressure differential across the engine.  Plus the chemistry of gasoline is such that it will not burn completely.  

 

Fuel efficiency starts with obtaining as complete a combustion of the fuel as possible, then using as much as possible of the heat of combustion to drive the crankshaft.  Beyond that is is about reducing friction within the engine, then in the rest of the drivetrain.

My first tractor was a CIH MX135; for a time I owned a New Holland TM120.  Both tractors worked side by side running exactly the same load.  The TM used .9 gallons per hour more than the MX which is close to 25% more.  TM was a 7.5 liter I-6 turbocharged with an air to air charge cooler, the MX was a 5.9 liter I-6 turbocharged with no charge air cooling.   

[acem]

A gasoline engine is always making a vacuum which takes energy which reduces efficiency.

Diesels don't have a throttle plate so they don't make a vaccum.

[oleman]

1 hour ago, acem said:

A gasoline engine is always making a vacuum which takes energy which reduces efficiency.

Diesels don't have a throttle plate so they don't make a vaccum.

BUT the diesel engine has a high compression to produce so the basic engine cost more to produce and a very complicated fuel system that also eats up efficiency. Does a diesel last longer; I doubt it if the base engines were the same, wonder what the lng version of the Cummins  lives like in the transit bus industry as compared to the base diesel version.

 

[Gearclash]

A gasoline engine built like a diesel will last about the same but gasoline can never match the energy conversion efficiency on account of the gasoline fuel being limited by compression ratio and by its own chemistry that doesn’t allow for complete combustion. 
 

From an energy accounting standpoint, most of the energy used to generate the higher compression pressures in a diesel is returned to crankshaft/flywheel, and ditto the energy required to inject diesel fuel. 
 

Higher compression ratios allow for a longer expansion after combustion; longer expansion allows for a better ‘harvest’ of the heat generated rather than losing the heat out the exhaust.  For further reading on this see how the Atkinson cycle takes advantage of compression/expansion by modifying the compression side of the cycle. 
 

True E85 has an octane rating around 109; it can tolerate a compression ratio much higher than any regular gasoline and if an engine is built to fully utilize that capability it is possible for the mileage of that engine to come close the mileage of an engine running on regular gasoline even though E85 (actual) has only 68% the energy of E0. 
 

Edit to correct: I think E85 is 72% the energy of regular gasoline and it is pure ethanol that is 68% the energy of regular. 

[Little Red]

My old friend Roger has a worn out 1466 that he ran a mixer wagon with, he would fill it with fuel on Saturday and run it all week to feed his cattle and refill it with fuel the next Saturday. His son in law talked him into buying a pretty nice 4430, I think the only thing that didn’t work was the fuel gauge,  he decided he would use the 4430 to feed cattle with, with the same exact mixer wagon feeding the same exact ration to same exact cattle and made it to Wednesday or Thursday before running out of fuel after filling it up the previous Saturday. He was fairly disappointed with the deeres drinking problem! 

[Chester5732]

19 minutes ago, Little Red said:

My old friend Roger has a worn out 1466 that he ran a mixer wagon with, he would fill it with fuel on Saturday and run it all week to feed his cattle and refill it with fuel the next Saturday. His son in law talked him into buying a pretty nice 4430, I think the only thing that didn’t work was the fuel gauge,  he decided he would use the 4430 to feed cattle with, with the same exact mixer wagon feeding the same exact ration to same exact cattle and made it to Wednesday or Thursday before running out of fuel after filling it up the previous Saturday. He was fairly disappointed with the deeres drinking problem! 

How did the size of the fuel tanks compare?

[Little Red]

10 minutes ago, Chester5732 said:

How did the size of the fuel tanks compare?

4430 has a 46 gallon tank, 1466 has a 42 gallon tank. That makes it even worse 😂, I knew they were similar in size but had to look it up to tell you exactly how much. 

[acem]

11 hours ago, oleman said:

BUT the diesel engine has a high compression to produce so the basic engine cost more to produce and a very complicated fuel system that also eats up efficiency. Does a diesel last longer; I doubt it if the base engines were the same, wonder what the lng version of the Cummins  lives like in the transit bus industry as compared to the base diesel version.

 

Diesel engines also have a high pressure fuel system that consumes a good bit of energy whatever form it is.

I believe if they would design a gasoline engine that ran without a throttle, it would have much better efficiency.  I don't understand why it has not been done since the cars are all computerized fuel injection. 

[snoshoe]

44 minutes ago, acem said:

Diesel engines also have a high pressure fuel system that consumes a good bit of energy whatever form it is.

I believe if they would design a gasoline engine that ran without a throttle, it would have much better efficiency.  I don't understand why it has not been done since the cars are all computerized fuel injection. 

Well they've tried. Texaco had one in the 70's. They were injecting fuel past a spark plug. Sometime later I read where someone else was working on it. Don't know what the stumbling block was.

[Gearclash]

1 hour ago, acem said:

Diesel engines also have a high pressure fuel system that consumes a good bit of energy whatever form it is.

Can't comment on the efficiency of high pressure common rail but on the distributor injector systems most of the energy used to generate the high pressure is returned back to the crankshaft. 

[jnbru]

The AI answer I already knew, But I thought range was 12:1 to 50:1 diesel engines. Gas engine are only 12:1 to 14:6 or you have engine damage.

 

AI "The air-fuel ratio (AFR) in a diesel engine varies dynamically from 15:1 to over 100:1 depending on engine load, maintaining a lean operation because power is controlled strictly via fuel injection rather than airflow regulation. While the theoretical stoichiometric ratio (complete chemical balance) for diesel fuel is approximately 14.5:1 to 14.6:1, a diesel engine rarely runs at this level to avoid dense black smoke and extreme heat."

[Diesel Doctor]

Gas engines are now running a similar diesel common rail system for direct injection gasoline. 

So they are controlling HP/economy by the amount of fuel injected to the cylinders.

The computers have aided emissions and HP and will probably get better in the future.

This has also caused carbon buildup on the intake valves. 

Something that shouldn't happen, but it does.

Until something is invented to replace oil, we are stuck with it so we need to make the best of it.

Wishing a change, like electricity, fell flat on it's face in most markets.

[New Englander]

It's hard to compare older gas auto engines with the later ones. Things like VVT increase fuel mileage by up to 10%, generally around 6% in all-around and reduces emissions without EGR. Fixed cam timing cannot match it. Direct port injection computer controlled along with variable ignition timing is another advantage vintage engines don't have. Watch a scan tool's data stream while driving or preferably while someone else is driving and see how much the engine computer is varying everything to maximize efficiency and driveability. AF ratios vary according to load as does timing. There's no way a vintage carburetor engine with fixed everything can match it.

Driving down the highway in an older car the only thing that might change is ignition timing due to the vacuum advance responding to higher manifold pressure. Watch the timing on just a constant speed mild downgrade in a computer controlled engine go waaaayyyy advanced. A/F ration will go leaner too. 

[Diesel Doctor]

1 hour ago, New Englander said:

It's hard to compare older gas auto engines with the later ones. Things like VVT increase fuel mileage by up to 10%, generally around 6% in all-around and reduces emissions without EGR. Fixed cam timing cannot match it. Direct port injection computer controlled along with variable ignition timing is another advantage vintage engines don't have. Watch a scan tool's data stream while driving or preferably while someone else is driving and see how much the engine computer is varying everything to maximize efficiency and driveability. AF ratios vary according to load as does timing. There's no way a vintage carburetor engine with fixed everything can match it.

Driving down the highway in an older car the only thing that might change is ignition timing due to the vacuum advance responding to higher manifold pressure. Watch the timing on just a constant speed mild downgrade in a computer controlled engine go waaaayyyy advanced. A/F ration will go leaner too. 

Getting rid of the EGR valve is one of the blessings for longer engine life.

[acem]

2 hours ago, New Englander said:

It's hard to compare older gas auto engines with the later ones. Things like VVT increase fuel mileage by up to 10%, generally around 6% in all-around and reduces emissions without EGR. Fixed cam timing cannot match it. Direct port injection computer controlled along with variable ignition timing is another advantage vintage engines don't have. Watch a scan tool's data stream while driving or preferably while someone else is driving and see how much the engine computer is varying everything to maximize efficiency and driveability. AF ratios vary according to load as does timing. There's no way a vintage carburetor engine with fixed everything can match it.

Driving down the highway in an older car the only thing that might change is ignition timing due to the vacuum advance responding to higher manifold pressure. Watch the timing on just a constant speed mild downgrade in a computer controlled engine go waaaayyyy advanced. A/F ration will go leaner too. 

This is all true but there is often more to it.

My wife's Geo Metro XFI gets over 50 MPG. Simple computer with throttle body injection. Standard cam with non interference engine. Very light and simple car. It has a quarter million miles on the original engine and transmission now. We've driven it all over from the south, midwest, beaches of Texas (you can drive on many beaches in Texas), Key West, etc. 

No gasoline powered,  non hybrid car available in the US can even come close to the mileage 30 years later. 

I don't understand why they don't offer conventional cars here in the US that get 50 MPG anymore. They are available in Japan, KEI cars.

[acem]

But I should quit complaining about  cars not getting 50 MPG and gas prices being so high. 

Every time I go to town I see vehicles in the parking lot with the engine and AC running while they are shopping. 

Obviously fuel efficiency is not that important and the cost of gasoline is not too high.

[Binderoid]

On 8/3/2026 at 10:08 AM, Drysleeves said:

their 560's made them so much money they could afford to buy a John Deere

I dont understand the upside to this purchase.

[oleman]

2 hours ago, acem said:

This is all true but there is often more to it.

My wife's Geo Metro XFI gets over 50 MPG. Simple computer with throttle body injection. Standard cam with non interference engine. Very light and simple car. It has a quarter million miles on the original engine and transmission now. We've driven it all over from the south, midwest, beaches of Texas (you can drive on many beaches in Texas), Key West, etc. 

No gasoline powered,  non hybrid car available in the US can even come close to the mileage 30 years later. 

I don't understand why they don't offer conventional cars here in the US that get 50 MPG anymore. They are available in Japan, KEI cars.

Yep. our 1600 CC NISSAN VERSA (105 HP)  made a  trip from my driveway to Springdale Ar a distance of 500+ miles on one 12 gallon tank of fuel, it has a normal 4 speed automatic and AC, without stopping.   The 93 Suburban with a 454 auto and 4 x 4 same trip on 1 tank of gas at the same speed of the versa, on tank of fuel or 38 gallons, street tires get better mileage than off road tires. in 1984 I had a Chevy Chevette powered by a 1.8 ltr 50 HP Isuzu diesel, 5 speed od manual commuted from Napa County to Santa Clara and got between 45 - 50 MPG for 140,000 miles. I once got  a speeding ticket going 65 MPH in a 55 mile zone, remember when the 55 MPH speed limit was attached to cars!  The little diesel could keep up with traffic flow.

[New Englander]

7 hours ago, acem said:

Very light and simple car.

Light is probably the answer. Unfortunately it probably couldn’t be made today and pass safety requirements. 
 

I’m really becoming sold on hybrid technology. Last week my wife and flew to Bar Harbor, rented a Toyota Camry hybrid, drove it all around then up to Lubec and East Port and back getting 51 mpg in a very nice car. I’ve had some other hybrid like Prius but they were not as nice. My wife has a ‘24 Traverse and it gets around 22 in mixed driving. I think a Highlander hybrid will be the next one. It seems batteries are lasting just fine and you never have to seek out a charging station.

[dale560]

42 minutes ago, New Englander said:

Light is probably the answer. Unfortunately it probably couldn’t be made today and pass safety requirements. 
 

I’m really becoming sold on hybrid technology. Last week my wife and flew to Bar Harbor, rented a Toyota Camry hybrid, drove it all around then up to Lubec and East Port and back getting 51 mpg in a very nice car. I’ve had some other hybrid like Prius but they were not as nice. My wife has a ‘24 Traverse and it gets around 22 in mixed driving. I think a Highlander hybrid will be the next one. It seems batteries are lasting just fine and you never have to seek out a charging station.

And the smart people at gm sold  or gave that technology to Toyota. Hybrid is probably the best option or a Honda generator in the trunk.

[Drysleeves]

11 hours ago, Binderoid said:

I don't understand the upside to this purchase.

Neither did I but it's what I was told.

[Diesel Doctor]

23 hours ago, acem said:

This is all true but there is often more to it.

My wife's Geo Metro XFI gets over 50 MPG. Simple computer with throttle body injection. Standard cam with non interference engine. Very light and simple car. It has a quarter million miles on the original engine and transmission now. We've driven it all over from the south, midwest, beaches of Texas (you can drive on many beaches in Texas), Key West, etc. 

No gasoline powered,  non hybrid car available in the US can even come close to the mileage 30 years later. 

I don't understand why they don't offer conventional cars here in the US that get 50 MPG anymore. They are available in Japan, KEI cars.

It's government that prevents it.

They would rather you burn more fuel to protect the environment.

Let that sink in?