Gas versus diesel in torque?

LJD · Dec 14, 2012

I hate to side-track the argument but gas engines make the same torque as diesel engine when they have the same bore and stroke and same aspiration. Sometimes more.

I've seen several mentions of diesels having more inherent torque then gas engines. Somebody show me some evidence of that? If anything the gassers tend to have a little more torque.

Too many peoples are comparing "apples to oranges." Long stroke diesels to short stroke gassers, or turbo-diesels to non-turbo gassers.

VERY easy to verify since many farm tractor made identical engines in gas and diesel versions. In just about every Nebraska test, the gassers beat the diesel versions. IH 144? Deere 144? Ford 172? All same bore and stroke and in gas or diesel versions.

Not the case with autos and truck. The only few I can think of were the Olds 350 gas and 350 diesel. The gas version had more torque and horsepower. Also the IDI Ford 7.3 non-turbo. IH built it for Ford and it started life as a HD truck gas engine used mostly in school busses. The gas version had more torque. Isuzu 1.8 and 2.2 liter diesels both first came in gas versions. Gassers had more torque and horsepower.

the tractor vet · Dec 14, 2012

I have had both , i have towed with FE block fords and 385 block Fords They all did a good JOB , BUT you had to keep them buzzing at or above 3400 RPM or they fell flat on there face , I have run Gas powered semi's from way before you were out of dippers and BEFORE the turbo was on MOST diesel trucks and i can tell ya that a diesel would pull far better then a gasser and longer on less fuel. Now today we have the turbo on both gas and diesel but the raw pulling power on the diesel at a lower engine RPM will do far better last longer .

chucksoliver77 · Dec 14, 2012

LJD, i agree with you, i'd like to see a 3.5L diesel that can match the ford ecoboost in torque 425lbft and 365hp and run the 1/4 mile in `14.9 seconds at 95mph.
and get 10+mpg towing 11500lbs and 22 mpg highway mpg. mine does exactly that. you don't need to wind the sh!t out of it either, makes 90% torque 1700rpm and max @2500. it's just amazing how long it stays in 6th gear when towing a heavy load. chuck

TMo · Dec 14, 2012

I agree. It seems to be a perception that as a generalization the term diesel's automatically have more torque or pulling capability.

You are correct, there is data to show comparable gassers have more hp and torque.

Example: Ford 460 with a 4.10:1 gear ratio will perform just as well as a comparable diesel, IMO

MSD · Dec 14, 2012

All the way to the gas station anyway.

TMo · Dec 14, 2012

You are right about mpg....

uncle henry · Dec 14, 2012

04 dodge 3500 with cummins 6-speed trans trailer 48 foot deck empty weight 8,600 20 5x5 roll of hay equals 39,760lbs i have had a 97 chevy with a 454 i get twice the miles per gallon and pulling with the dodge only things i have that are gas powered are tractors and grandfather's 1965 f-100 that he bought new

Bob Huntress · Dec 14, 2012

The small cars like Rabbits and Chevy Luvs were available with diesel because world wide diesel was more available in the late 1970"s and 1980"s and at times was cheaper than gas. Small vehicles that never haul much load don"t realize an advantage to diesel. If you haul loads diesel is more effecient than gas, but unless you are hauling load, there isn"t an effeciency gain with diesel.

casenut1 · Dec 14, 2012

i have always liked the 300-6 from Ford . has lots of torque. pulls nice when geared properly.

rrlund · Dec 14, 2012

Wouldn't take much of a gas engine to have more HP and torque than this old NA 6.9 diesel in my Ford. That thing's a dog.

But yea,I'll agree to apples and oranges. Oliver was the first to really popularize diesel engines in tractors with better'n 50% of the market there for a while,and in several models,the diesels were a larger displacement.

jm. · Dec 14, 2012

Chuck are you talking about a 0 12 f 150 with the e co boost .. I have learned how to fool mine into staying into 6th gear forever. It pulls hills like a big truck, loads down but just keeps getting it. Haven,t had anything over 4 thousand lbs or so but pulling a trailer it does pretty good. Haven,t seen 22 mpg but no problem staying around 20.

buickanddeere · Dec 14, 2012

I see the apples and oranges comparison is alive and well.
How can you compare a poc carbureted or throttle body 454 to a pre 2007 diesel? Of course the diesel is ahead of the game.
Now lets move up to 2013 diesel vs and a new direct injection 6.2 or Ford 3.5 and then compare. Up front cost, regular service, cost of fuel per gallon, mileage and repairs out side of warrenty.
Don"t know why you guys keep trotting out decades old history.

chucksoliver77 · Dec 14, 2012

jm., mine is a 2011 reg. cab 4x4. i have a hard time getting 22 but it can be done, it's just hard to keep away from using all that power lol. chuck

Longmeadow farm · Dec 14, 2012

The Tractor Vet has it right. The diesel engine physics is different than the gas. It produces maximum torque at a much lower RPM than a gas job and with far less fuel. As I'm an electrical engineer and not a mechanical engineer I don't have all the answers and don't presume to know things out of my area of expertise. But what I do know is that a diesel under load reacts quite differently than a gas/ignition engine under load. In order to fully understand the physics of each technology you would have to study the HP, torque and fuel usage curves. Not all diesel engines are created equal. Many of the older diesel designs are a bit weak in the torque/lugging department, while the more recent designs are light years ahead. John Deere offers an economy PTO that runs 540 at 1700 engine rpm... and not at 2400 engine RPM..why?.. because max torque is achieved around 1700 and while max HP is achieved near the rated speed of 2400 it is not necessary to power most PTO implements, and I realize a 30-35% fuel savings.

dhermesc · Dec 14, 2012

Ever take a car or pickup on the road and shift at the peak torque RPMs? You won't be setting any speed records.

buickanddeere · Dec 14, 2012

(quoted from post at 16:11:09 12/14/12) The Tractor Vet has it right. The diesel engine physics is different than the gas. It produces maximum torque at a much lower RPM than a gas job and with far less fuel. As I'm an electrical engineer and not a mechanical engineer I don't have all the answers and don't presume to know things out of my area of expertise. But what I do know is that a diesel under load reacts quite differently than a gas/ignition engine under load. In order to fully understand the physics of each technology you would have to study the HP, torque and fuel usage curves. Not all diesel engines are created equal. Many of the older diesel designs are a bit weak in the torque/lugging department, while the more recent designs are light years ahead. John Deere offers an economy PTO that runs 540 at 1700 engine rpm... and not at 2400 engine RPM..why?.. because max torque is achieved around 1700 and while max HP is achieved near the rated speed of 2400 it is not necessary to power most PTO implements, and I realize a 30-35% fuel savings.

That's because a diesel or gas turbine has lousy part load fuel efficiency. The extra air swept through the engine that isn't used in combustion. Just carried heat out the stack instead of performing work.
Of course a diesel at 90% load at 1700 rpm making 40HP will burn less fuel than the same diesel operating at 2400rpm, making 40HP and operating at 64% load.
Take a look at the fuel consumption curves of a diesel making 20% of rates power rolling down the road vs a gasser making 20% of rates power rolling down the road.
Also compare fuel efficiency of a 90% loaded diesel at it's peak torque rpms and a port or direct injection gasser making 90% of rated power at it's peak torque rpm.
Don't waste your time either talking about engine life when operating at 1500 and 3500rpm in momentary duty cycles in the light duty cycle of a pickup truck.

LJD · Dec 14, 2012

Nonsense. Show us one engine that came as gas and diesel and the diesel has more torque at lower RPM (with equal aspiration) I can show you many that do NOT.

Long stroke is what makes torque. Just like putting a piece of pipe on a wrench handle. Just so happens that most engines now adays with long strokes are diesels. Gas engines usually have shorter strokes to make higher RPMs.

One example of many:
Deere three cylinder engines with equal bore and stroke (except 135 gas has shorter stroke):

135 gas: 43 HP @ 2500 RPM, 110 TQ @ 1300 RPM
152 gas: 42 HP @ 2500 RPM, 110 TQ @ 1300 RPM
152 diesel: 42 HP @ 2500 RPM, 110 TQ @ 1300 RPM
164 diesel: 42 HP @ 2500 RPM, 110 TQ @ 1300 RPM

Ferd · Dec 14, 2012

Mine is the same - just amazing power and torque from a V-6. Pulls my 9,000# fifth wheel just as good as the diesel I sold. And no turbo lag and it"s just plain quiet even when pulling.

Diesels have their place but the new ones are not very forgiving like the older ones were. Cylinder pressures are off the chart compared to older diesels due to EPA requirements. To much water in the fuel can get past even the excellent filters they have and then you"re looking at no warranty and major dollars. Just read some of the diesel forms.

But, you can still rationalize anything you want to buy weather it makes any sense or not.

buickanddeere · Dec 14, 2012

(quoted from post at 16:51:32 12/14/12) Nonsense. Show us one engine that came as gas and diesel and the diesel has more torque at lower RPM (with equal aspiration) I can show you many that do NOT.

Long stroke is what makes torque. Just like putting a piece of pipe on a wrench handle. Just so happens that most engines now adays with long strokes are diesels. Gas engines usually have shorter strokes to make higher RPMs.

One example of many:
Deere three cylinder engines with equal bore and stroke (except 135 gas has shorter stroke):

135 gas: 43 HP @ 2500 RPM, 110 TQ @ 1300 RPM
152 gas: 42 HP @ 2500 RPM, 110 TQ @ 1300 RPM
152 diesel: 42 HP @ 2500 RPM, 110 TQ @ 1300 RPM
164 diesel: 42 HP @ 2500 RPM, 110 TQ @ 1300 RPM

Long stroke and small bore and short stroke with a large bore , with the cubic inches being the same. Doesn't make beans for difference in torque and power.
The small bore engine just doesn't have the room for large valves so it can breath at high rpms like the large bore engine.
Old tractor engines tended to be tall a narrow to fit the chassis so hence the long stroke, small bore engines where small valves and small ports . Would keep airflow velocity high and assist with low rpm cylinder filling.

RodinNS · Dec 14, 2012

You're absolutely correct... Probably the BEST DIRECT example is the Ford Basildon engines. They were designed as a diesel engine and were mostly uniform throughout the range having 3, 4 and 6 hole versions utilizing many of the same parts. These engines were then modified to spark ignition... but the bottom ends were identical. I believe the cam was also identical. Heads were similar... main difference to drop the comp ratio was in the pistons. The gasoline engines made considerably ~more~ power on the same displacement... so they generally used a bit smaller displacement on the gas engines for the same model tractor so as to keep the power level the same. I suspect that peak torque for a given displacement WAS the same but the spark engines were probably a bit more top ended on power which is why they made a bit more....

So as it applies to the previous arguement... I think if you had a direct injected spark ignition engine built to diesel specs... with a turbo... you'd probably get pretty similar performance to a diesel engine... and mabey even close to the efficiency we've known from diesel's.

Rod

LJD · Dec 14, 2012

If you were running big rigs before I was out of diapers, you must be in your 80s? That's fine and congratulations. Proves nothing about the subject at hand.

Tell me about any Ford gas engine in a HD truck that had a 4" or more stroke? I'm all ears. Maybe the 534? It's the only one I know of and it wasn't an FE series engine. 4.5" bore by 4.20" stroke, 481 ft. lbs. of torque at 1600 RPM.

In lighter use, the Ford 300 straight-six was one of the longest stroke engines made for torque in lighter rigs.

Mack had a pile of long-stroke gas engines.

707 cubic inch gasoline Mack had 5" bore by 6" stroke. 232 horse @ 2100 RPM and 617 lbs. of torque @ 1200 RPM.

707 cubic inch diesel Mach had 5" bore by 6" stroke. 201 horse @ 2100 RPM and 602 lbs. of torque @ 1500 RPM.

Mack's "little" 464 in gas and diesel:

464 gas engine, 464,cubic inches, 4 7/16" bore by 5" stroke, 185 horse @ 2800 RPM and 380 lbs. torque @ 1400 RPM

464 diesel engine, 464 cubic inches, 4 7/16" bore by 5" stroke, 140 horse @ 2600 RPM and 325 lbs. torque @ 1800 RPM

uncle henry · Dec 14, 2012

go get both and tell me how it goes

LJD · Dec 14, 2012

Yes it would be interesting to see what could be achieved with a high-tech HD gas engine with all the latest tweaks. It's already been done with some big-rig natural gas and propane engines (to a degree).

GM and a few Asian companies had been working diesel-principle engines that run on gasoline. No spark ignition. Haven't heard much about it lately.

Joe(TX) · Dec 14, 2012

It appears you have already made up your mid on the matter and no amount of evidence will change that.
Its not about the most torque or horsepower.
The question is at what rpm the peak torque is at. A gas reaches peak torque at a high rpm. The diesel is normaly at at much lower rpm. The peak torque at a lower rpm makes the torque more usable. If you lug the rpm below the peak torque, the engine will continue to pull down.
You mentioned the Ford 172 as an example. I will tell you that the diesel, with a lower horsepower, will outpull a gas motored one. I have had both.
As an engineer I have studied the torque/horsepower curves on a lot of engines. That is where you get the real story.
The Dodge Hemi truck has the same hp as my diesel. Hook them bumper tp bumper an see who wins in a pulloff. Not to mention fuel economy and engine life.

uncle henry · Dec 14, 2012

how many 18 wheelers and trains have a gas engine none because they can't pull like a diesel

LJD · Dec 14, 2012

I also have studied diesels and gas engine for years. Also worked on many, ran many on dynos, and still use a few. You say no amount of evidence will convince me? What evidence? Show me anything. I am open minded.

Post even one shred of test data that proves your point and disproves mine.

I already posted many test specs that show gas engines making torque at the same low RPMs. I gave engine models and RPMs.

Show me even one example to the contrary?

And about owning an using them. I own several gas and diesel engines that share bore and stroke. IH BC144 and IH BD144. Deere 144 gas and Deere 144 diesel. Ford 172 gas and Ford 172 diesel. Case 188 gasser and a Case 188 diesel.

LJD · Dec 14, 2012

Truck companies use trucks that will move the most goods at the lowest cost per mile. Diesels to date - in heavy use do the job more efficiently. That fact has nothing to do with the argument. A gas engine built to the same bore and stroke as the diesels out there - with turbocharging and intercooling would outpower the diesels. But they would also be pigs on fuel use.

BushogPapa · Dec 14, 2012

As for efficiency....the 350 Olds Diesel would get 30+ MPG in a Caprice Station Wagon..
The 350 Olds Gas engine would not ever come close to that..

Ron..

Fritz Maurer · Dec 14, 2012

John Deere? Light years ahead? The Ford 9700 had a PTO speed of 540/1000 at 1800 in 1977. It was also part of a very small group of tractors where the remotes were adjustable from inside the cab. None of them were green.

Rick Kr · Dec 14, 2012

Be careful loading the truck in 6th gear too hard, you'll end up smoking the trans. Watch your trans temp when you are climbing the grades, and not letting it drop back to 5th or 4th.

If you are very lightly loaded, it likely isn't going to be a big deal though.

Rick

buickanddeere · Dec 14, 2012

(quoted from post at 19:24:18 12/14/12) how many 18 wheelers and trains have a gas engine none because they can't pull like a diesel

Dam, are you dense between the ears? You are comparing light duty and heavy duty applications.

RodinNS · Dec 14, 2012

All I can think of right now is the BIG Moline... G1050 or whatever it was? Something like a 600 cube spark engine... Big power. Even bigger fuel usage. I'm sure it had low end torque in ample reserve tho.

Rod

RodinNS · Dec 14, 2012

Most diesels make low end torque and most gas engines make high end power because that's what their designers intended them to do, not because there in anything inherent in one or the other that dictates that result. Cam profile/duration and stroke length are largely what dictates engine breathing, thus it's torque curve.

If you were to root out the nebraska test results for the Ford 3000 and 5000 tractors in both the gasoline and diesel versions using the 175 cid and 233 cid engines respectively I believe you'll find that they have almost identical curves... much to the point that the profiles are the same excepting that the spark engine will probably achieve peak torque at 100-150 rpm faster than the diesel. This will result in the spark engine being a bit prouder on the top end because the torque rise was basically identical to the diesel. Again... SAME cam shaft in both. Same lift. Same duration. Same stroke and displacement.

Rod

Gas versus diesel in torque?

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