Oil & Fuel Diesel HP vs Gasoline HP

keeney · Feb 13, 2004

OK, assuming gearing appropriate to get the tires to spin.

Once they are spinning the point is that the RPM's can be kept up in the engines torque sweet spot.

So, imagine two machines, both with the same weight and the same tires. One is spinning the tires about 3x faster than the other. Which one is pulling harder?

On the other hand, if both machines have enough traction to keep the tires stuck, the diesel tractor will win because it can make more torque at the near-zero RPM while the truck's gas engine will not be able to remain on a high point of its torque curve. Maybe the truck driver can burn enough clutch to compensate?

- Rick

BillyP · Feb 13, 2004

So, imagine two machines, both with the same weight and the same tires. One is spinning the tires about 3x faster than the other. Which one is pulling harder? 

I don't know but spinning tires don't pull much. Once you get the tires spinning, you need more traction. Once you get enough traction to keep the tires from spinning, the torque comes back into play.

 Maybe the truck driver can burn enough clutch to compensate? 

Once you 'burn' the clutch, you're gaining RPMs but loosing your momentum. You're taking away from the tires and giving it to the engine.

keeney · Feb 13, 2004

Eventually, spun fast enough, some tires in dirt or other soft materials produce more forward thrust than the maximum static traction. I think it has something to do with the material ejected producing a thrust. I do know that top fuel pulling tractors all spin like crazy.

On burning the clutch, the point is that the 290 HP truck has 200 HP extra to burn in order to get up to the same torque on the curve as the 90 HP tractor. The clutch will of course be toast after this, but with the right torque curve, this may be a way to beat the tractor.

Kyle_in_Tex · Feb 14, 2004

RalphVa hit the nail on the head.
It is commonly known among gear heads that:
1)Increasing compression gives more HP/torque, this can be done by changing piston/head chamber geometries, turbo or stuffer/blower.
2)More compression blows head gaskets or breaks other stuff if not properly engineered. Just ask anyone who owned a GM 5.7 L diesel engine about head gasket problems.

So, yes, more compression is good if it can be contained. This is why diesels cost more...Kyle

Ledgemere Farm · Feb 14, 2004

Plus the Case will probably have alot more rubber hitting the ground. I'd like to see a 25 HP Briggs run a 5' Bush Hog...

Soundguy · Feb 15, 2004

And drive the tractor and operator around while doing it.. and not stall out when it hits the first blade o' grass.

If they rated tractor engines like they rated lawnmower engines.. I have a feeling that a 8n would be 38 hp maybee 42.. etc... ( ungoverned, and at detonation speed... etc ).

Soundguy

nomad · Feb 15, 2004

( Two identical compact tractors with 25HP engines except one is gasoline and the other is diesel. Why is the diesel so much more powerful? Answer: Because the torque of a gasoline engine is generally a small percentage, greater or smaller, than its HP rating while the torque rating of a diesel engine is almost double or even many times greater than its HP rating. )

If the torque is small, then the speed must be high. (to satisfy the constant hp power equality) - Lets see what the power means: (I'll use this "~" sign as a relation sign, not equality sign.)

P (hp or watt, doesn't matter) ~ Force x Velocity
If it's a rotational motion like we see in the engine flywheel,
we can also write its rotational motion form of Power by using Angular velocity or the frequency or the RPM and by replcing Torque = Force x Length.

For engine flywheel;
Power ~ Torque x RPM
or its open form:
Power ~ Force x Size of Flywheel x RPM = F x S x RPM

Now, you said SAME HP for gasoline and diesel?
Then, there is this equality;
Fg x Sg x RPMg = Fd x Sd x RPMd
where g subscript shows gasoline and d subscript shows diesel.
Now, if flywheel sizes are same, then Sg will be equal to Sd and will cancel each other. Then,
Fg x RPMg = Fd x RPMd
So, if your diesel applies double force than the gasoline of the same HP, then RPM of diesel will be half of the RPM of gasoline.

MossRoad · Feb 15, 2004

No one's explained WHY diesel engines have more torque. 

Diesel engines have more torque because they have a longer stroke. The longer stroke is like a longer lever on the crankshaft. More leverage equates to more torque.

MossRoad · Feb 15, 2004

Here's a link to really good explanation of why diesels have more torque.

http://auto.howstuffworks.com/question381.htm

4710and110TLB · Feb 15, 2004

I am new in this discussion but first of all a gas engine and a diesel engine are two totally seperate beasts. Diesel fuel has the ability to pruduce something like 4 times the power than a gas engine. 1 Gallon of diesel equals something like 1000 hp at 100% effeciency where as a gas engine can only make 250 hp. The people talking about higher compersion ratios getting more power are partially correct. On a gas engine if you raise the comp. up to say like 14.0:1 then you must use a higher octane fuel or else the fuel will detonate and knock. A diesel engine doesn't care so long as it is at like 15.0:1 which is the absolut lowest it can be so that the air gets hot enough when compressed to ignite the vaporized diesel molecules. Which most trucks run at 18:1 and smaller diesels with non turbos run low to mid 20:1 ratios. The more air you can cram into a cylinder the more fuel you can burn. No oxygen no power. Thats why we put turbos and superchargers on engines. So you can get more oxygen to burn more fuel. A diesel engine gets more torque due to diesel burning rather than like exploding gasoline. Its powerstroke takes longer to happen which puts a longer and more powerful force on the pistons head. Diesel engines like I6's are designed with a really long stroke to give the pistone and connecting rod more leverage on the crank. The longer the stroke is the slower an engine can turn. That is why a gas motorcycle with an 1.5 or 2 inch stroke can turn 15000 rpms as where a 15 liter caterpillar engine will turn under 3000 rpms. Another example is ford 6 liter psd. It was designed with a shorter stroke so it would redline at 4300 rpms where the dodges redline at 3000 or 3300 rpms. And my last point when dealing with tractors horse power is nearly irrelevant. Torque is what get the work done. Horsepower will get you down the road, torque will get you down the road with 30000 lbs in tow. All the horsepower/torque in the world is pointless if you can't get it to the ground. That is why tractors have big tires wtih big lugs and trucks... well you get the idea now I hope. So remember a 25hp gas and 25hp diesel engine will be able to to the same weight lifting in the same time it jsut a diesel can do it at a slower rpm since it should have more torque. All right I am tired of typing and you have go to be tired of reading now, so I am done. /forums/images/graemlins/blush.gif /forums/images/graemlins/crazy.gif