Diesel vs gas

[buickanddeere]

Back in the 70's I was working as an engineer for Cleaner Combines. We used the same basic engine gas or diesel but the gas wouldn't handle slugs fed into the combine like a diesel. Slug -- poor -- dead -- dig the slug out. So we changed to GM gas engines to get more gas engine power. Combine 155 HP from a Chef 350 gas or 130 from a turbo 301 Allis-Chalmers. Same result except sucking a tremendous amount extra fuel when fuel prices were skyrocketing with $1 per gallon in site. Bit the bullet and dropped the gas, or rather the customers did it for us.

I have a Kubota M7-171 rated by Kubota at 140 PTO up. The Nebraska test shows it put out slightly more HP at the E PTO 1600 rpm than it did at the rated PTO 2000 rpm. Since HP=2 × pi x T/33,000 the torque has to really climb to get more HP at 1600 than at 2000. Our JD 7720 is even better rated at 130 PTO but by the Nebraska test peaking at 170 HP as it pulls down.

I grew up with Far all H's and M's but what a difference when we got our first diesel - except for starting at 40 below. It didn't, but the Farmalls were still around.

Check you formula and math . The HP does not increase as the engine luggs down to the torque peak.

 

[ovrszd]

Have a look at the tachometer on a 4020 gas and a 4020 diesel. The gasser makes more HP per cubic inch at the same 1900 rpm for PTO. The 4020 gasser is not turning 3500-4500rpm.

I was referring to his trucks.

 

[ovrszd]

Nah. My late 70's IH2500b had a gas engine and PTO speed was about 2400rpm, as I recall. I'll have to pull the manual and check it.

Jeez, another one. I was referring to his trucks.

 

[ovrszd]

I remember hearing about a well drilling rig around here. The got it with a Dodge V10, and it got like 3mpg for them. Needless to say; they got a Cummins when the V10 mysteriously burned up. I think the B5.9t got like 12mpg or so. Not too surprising. Those 8.0ls were always thirsty.

And turned twice the rpms.

 

[MossRoad]

I was referring to his trucks.

Jeez, another one. I was referring to his trucks.

This is a tractor forum! :laughing:

 

[ovrszd]

This is a tractor forum! :laughing:

I didn't mention trucks, he did.

 

[MHarryE]

Please do a little research on modern mid and large ag tractor engines. Its been a long time since torque backup has been so large on diesels that there is a horsepower increase. I was in error citing the numbers on our 7720. The real numbers are 141.89 horsepower at 2100 rated engine speed and maximum horsepower is 159.69 at 1650 rpm. That is 355 lb-ft @ 2100 and 511 lb-ft @ 1650 or an excellent 44% torque backup. You don't see that kind of torque backup in SCUTs or CUTs but its expected in mid and large ag although I don't recall seeing any tractor bettering our 7720s 43%. Having 30% backup is considered a minimum.

At Gleaner we established a constant horsepower from rated engine speed to peak torque. This insured we had adequate torque backup for tough spots. Then we were purchased by Deutz who dictated, "We do not care about your requirements, this is the engine you will use". Things went downhill from there.

By the way my avatar is a diesel cycle explaining why a diesel has more pulling power than a gas engine although with proper equipment a gas engine can be built to nearly match a diesel.


Here is a simplified explanation from GrainNews:


Torque Rise Explained - Grainews

 

[Texasmark]

Biggest difference is torque: lots more with diesel, probably a result of the higher compression ratio.

I don't know where compression plays into it other than to get x number of hp out of a given space. The compression on a diesel generates heat as the air is compressed (compression ignition). The heat is what explodes the fuel vapor since there is no spark plug like in a (spark ignition system). That's why low compression engines, needing overhaul are "addicted" to ether. The older they get the worse the compression the harder to start.....the addiction thing has nothing to do with ether, it's all about compression. Diesels usually are under square with a long stroke and the purpose it to have a long burn period of the fuel to keep the foot-lbs flowing and to help in developing the compression ratio.....that's why 2 strokers are low on torque for the engine size and have to run high rpms.....Old OMC outboards at 25 hp were 30 cu in and ran 4500 rpm. Mercs ran 1 cu in/hp and up and ran at 5500-6000. Half way down the power stroke (every rev on them) the exhaust ports open and out goes the charge. If you didn't get the bang out of your fuel by then you just lost it.

Remembering hot rods of the 60's where they ran 10:1 compression and had to run high test, premium fuel to prevent self detonation, pre-igniton, pinging, or what ever you want to call it. High compression "Edelbrock" for a name got more bang out of a given block due to more compression.

 

[MossRoad]

I didn't mention trucks, he did.

DOH! :laughing:

 

[MossRoad]

Please do a little research on modern mid and large ag tractor engines. Its been a long time since torque backup has been so large on diesels that there is a horsepower increase. I was in error citing the numbers on our 7720. The real numbers are 141.89 horsepower at 2100 rated engine speed and maximum horsepower is 159.69 at 1650 rpm. That is 355 lb-ft @ 2100 and 511 lb-ft @ 1650 or an excellent 44% torque backup. You don't see that kind of torque backup in SCUTs or CUTs but its expected in mid and large ag although I don't recall seeing any tractor bettering our 7720s 43%. Having 30% backup is considered a minimum.

At Gleaner we established a constant horsepower from rated engine speed to peak torque. This insured we had adequate torque backup for tough spots. Then we were purchased by Deutz who dictated, "We do not care about your requirements, this is the engine you will use". Things went downhill from there.

By the way my avatar is a diesel cycle explaining why a diesel has more pulling power than a gas engine although with proper equipment a gas engine can be built to nearly match a diesel.


Here is a simplified explanation from GrainNews:


Torque Rise Explained - Grainews

I think I get it, but what's the difference between torque rise and just fudging the numbers to under-rate an engine's specs so it seems like you're getting some magical power out of it more than it's rated for?