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How to compare hp diesel v. gas


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#16 tractor buddy OFFLINE  

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Posted May 02, 2011 - 06:19 PM

very well put. Thank you
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#17 Oldeerethanme OFFLINE  

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Posted May 23, 2011 - 07:37 AM

Comparable diesel hp/torque is 1.42 times that of a gas burner.
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#18 Guest_jdecker94_*

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Posted July 02, 2011 - 08:56 PM

now i though with diesel, as you rpm's dropped, lets say while plowing snow, you would hit lets say 1600 rpm which would max out your torque and provide maximum torque, not hp. gas and diesel are funny with differences like that.
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#19 chopperfreak2k1 OFFLINE  

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Posted July 03, 2011 - 05:30 AM

i agree with jdecker. the point of a deisel is not it's hp but it's torque. it is the massive torque that makes a lesser hp deisel feel like a bigger gas motor. let's not forget hp is your ability to accelerate, torque is your ability to resist stalling. just my .02
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#20 Boss 448 OFFLINE  

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Posted July 05, 2011 - 01:55 PM

let's not forget hp is your ability to accelerate, torque is your ability to resist stalling


I like that way of explaining it.
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#21 Utah Smitty OFFLINE  

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Posted August 25, 2011 - 09:28 PM

I think you are right Daniel, I don't remember the model number, but it's in a T1600 tractor that my friend and I got for him to use as parts machine and for me to have a diesel engine for a conversion...:laughingteeth:


The Kubota T1600 tractor had the Z-482 engine. I have a Z-482 as well--came out of an APU for diesel tractors--provides 12V power, A/C, and heat without running the main engine. I think I may have a manual for it... check the engine manuals... if it's not there, I'll download it.

Utah Smitty
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#22 Cvans OFFLINE  

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Posted August 26, 2011 - 11:49 PM

From what I have observed in researching these small diesels is you have to watch were your information originates. There are several spec sheets out there on the net originating in Australia and Europe that show the horse power ratings 2 horse power or more lower than what they are rated at in this country. Metric horse power must be different than ours. :confuse:

In this country the Z400 is rated at 10hp max. The Z430 is rated at 12hp max. The Z482 should be approx. 14hp max. and the Z620 at approx. 16hp max. I know for a fact that my Z620 will easily put my Z430 to shame and both engines are running great.
And for those that aren't aware of this, the numbers following the letter in the engine model is the total displacement of the engine in cubic centimeters.

Edited by Cvans, August 26, 2011 - 11:57 PM.

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#23 KennyP ONLINE  

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Posted August 27, 2011 - 04:26 AM

Though I do not have any diesels, the info you posted last is nice to know, Chris. Thanks.
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#24 JDBrian OFFLINE  

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Posted August 28, 2011 - 07:35 AM

This is a very interesting topic. I am going to put my 2cents worth in. If I am wrong in anything I write here please correct me. I want to learn more about this topic.
I think there is a bit of a misconception out there about torque and HP. Torque is the amount of force produced by the engine. HP is that force multiplied by a constant and the RPM's. So HP is essentially the product of torque and engine speed. If 2 engines produce the same torque at the same RPM's then the HP will be the same regardless of the type of engine. As others have said, the difference in perceived power has more to do with the shape of the curves. A diesel is usually of a much larger displacement than a gas engine of the same HP. Torque is very dependant on displacement, so a larger engine will generally produce more peak torque. I'm not sure of the reason, but diesels produce peak torque at lower speeds. It is likely to do with the dynamics of diesel combustion. If you were to compare a gas engine and a diesel of equal displacement it would be a much closer contest.
The way I look at it is that when lugging under load, a diesel will almost always have more HP available then a similar rated gas engine. So under those conditions, which is what matters in the real world,the diesel is the higher HP engine and out performs the gas engine. It is HP that does the work.
A diesel is much more efficient than a gas engine at lower power levels. This is mostly to do with the pumping loss in the gas engine. Pumping loss refers to the intake vacuum in a gas engine that is caused by the throttle restricting the flow of air into the engine at small throttle openings. The engine is wasting energy by creating this vacuum. In a diesel the intake is wide open so there is a much smaller vacuum generated. The other major factor in Diesel efficiency is that the fuel has about 15% more energy/volume than gasoline. Even at wide open throttle the gas engine is at a disadvantage of 15%.
I think another factor is that the diesel is designed for continuous duty at high power levels and most of the gas engines used in modern GT's are not. The continuous ratings for a gas engine are much lower than the peak ones used in the spec sheets. The heavier construction of the diesel ensures that it can maintain high power output levels over a long lifetime. It is not uncommon to see diesel tractors with 10,000hrs+ on the clock. Sorry for rambling on!
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#25 DH1 OFFLINE  

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Posted August 28, 2011 - 10:33 AM

:ditto:

There is more energy, BTUs in a gallon of diesel vs gasoline.
Diesel engines have low if any, (non turbo) intake manifold vacuum, full charge of air every intake stroke.

The truck I drive at work has a 500hp Detroit Diesel in it, max governed RPM is 2250, power band 1300 to 2000 rpm, runs 35psi max turbo boost. Fully loaded it weighs 86,000lbs. You never see heavy trucks with gas engines in them because they just can't do the job. The diesel can run fully loaded maxed out for long periods of time because HP ratings are continuous not peak power IMO.
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#26 JDBrian ONLINE  

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Posted August 28, 2011 - 11:09 AM

Once you bring turbocharging into the mix then the HP/litre goes up dramatically for diesel or gas. In my post I really just wanted to say that torque and HP do not exist independant of one another. In the case of your truck it uses a large diesel and turbocharging to produce the HP needed at low RPM's.
I see that to get a larger number small engine manu. have been rating engines in Ftlbs of torque instead of HP. This is purely a marketing ploy. Some friends got a new self propelled lawnmower. They said it was 8.25HP and had lots of power. I looked at it and that was a torque number. The displacement was 190cc which will be roughly just over 6HP based on the common 30cc/hp rule. It probably won't be long before this happens in small tractors.
It is interesting how HP has increased in the trucking business. A friend of mine who has been trucking for almost 50 years remembers when he ran 265 or 300HP trucks on long hauls. He is now semi retired and runs a boom truck delivering concrete products. That truck has 450HP. I guess that's why you don't see many semi's slowing down to 30mph on hills these days.
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#27 DH1 OFFLINE  

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Posted August 28, 2011 - 11:23 AM

I drive a boom truck also, it was made to pull a trailer which we don't have for it, we have 3 old trucks in the 250 to 300hp range they carry 58,000lbs max and are gutless.
I'd like to add that I have been driving on the Hwy, going uphill, empty, and there are tri-axle dump trucks, loaded that out power and pass me going up hill, there loaded I'm empty. How much power they have???
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#28 Cvans ONLINE  

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Posted August 28, 2011 - 08:24 PM

There was an interesting statement made in another post that I think pretty much sums up the power available in these smaller engines. Small gas engines derive most of their horse power and torque at high rpm's. As they are loaded up their rpm's fall off and their torque and HP drop off drastically. Diesels on the other hand start developing their torque at much lower rpm's so as they are loaded up and the rpm's drop they are actually approaching their point of highest torque generation. Thus they are able to lug or power their way through the load. The multi cylinder short stroke diesels are less prone to this low rpm lugging power than the single cylinder long stroke engines.
Turbo charging and computer controls throw another whole dimension into the equation.
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#29 olcowhand ONLINE  

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Posted August 28, 2011 - 09:28 PM

Plus smoke from a gas engine is bad. Smoke from a hard pulling diesel is just so cool! :D
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#30 JDBrian ONLINE  

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Posted August 29, 2011 - 02:50 PM

Plus smoke from a gas engine is bad. Smoke from a hard pulling diesel is just so cool! :D


When I went to move up to a diesel CUT one of the issues I had was that the diesel was going to be so noisy and smelly. Many people had said to me how much the fuel and exhaust stinks, and all that smoke - yak,yak,yak etc.
What I have found is that it smells less than gas, the engine does not smoke unless you are working it really hard and the exhaust is not as objectionable to me as gas powered exhaust. When I walk into my garage I smell gasoline fumes from the 314 and don't smell diesel at all. The bigger tractor can do more work in less time using 1/2 to 2/3 the fuel of my old 23HP gas GT. I call that a win/win situation. And of course the sound is so so cool!
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