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  1. #71
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    Quote Originally Posted by RobertN
    Gas can last a long time. My comparison would be the 1941 Farmall A

    The Farmall motor red-lined at about 1600rpm(again, from fuzzy memory)

    After having that old tractor though, I bet that low rpm low compression motor would run forever, if maintained properly.
    Yours is similar to the old Massey Perkins gas engines which ran at 2000 rpm. I would think a gas engine using a diesel block running at 2000 rpm at a much lower compression ratio would last "forever". The advantage that diesel has at that point is the fact that diesel is a lubricant and gas a solvent. Too bad none of us would live long enough to wear either of these out given proper maintenance LOL. Modern high revving gas engines are a different animal.

  2. #72
    Platinum Member Carl Bert's Avatar
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    Quote Originally Posted by DarkBlack

    I see you have the normal "mindset" I was refering to Forget it's an engine comparison. Think as if you are comparing T.V.s.
    You have for the comparison, let's say $800. You can get a real big plasma, and compare it to a much smaller LED.
    So say you have $5k for the engine comparison. 5K buys you a nice big 400hp V8 gas engine. for $5,000 in diesel, you might get a 3 of 4 cylinder 40 HP engine. Now go put thos 2 engines in the same vehicles ( truck, tractor ). The big gas engine can be geared and run at a much lower relative load, and should last as long or longer. The same principal goes for weight.
    Did you ever think that you have the wrong mindset? It's like that joke where the wife calls the husband, on his way to work, and says "honey be careful, I just heard on the radio that there is some maniac driving the wrong way on the expressway". He says "there's not just one, there are hundreds of them".

    Your idea just isn't a fair comparison, you are not comparing two equal items. The engine must fit the task at hand. You're saying use a 40 HP diesel in place of where you would normally use a 400 HP. It just does not make sense. Obviously the motor will burn out prematurely, because you are not using it for what is was designed and built for. You would be overloading it and that would kill any engine.

    If you NEED to put a dollar value on the engines first, then it would have to go something like this. Purchase the recommended size diesel for the task at hand. Lets say its 250HP and costs $25,000. Now you have $25,000 to build a 250hp gas engine, which could now be built with much better quality materials than you would find in your average gas engine. Now you're comparing apples to apples. Run them both, under equal load, and see which lasts longer.

    Unfortunately we don't have the "better built gas engine" option in everyday life, so what's the sense. Thats why I think the comparison I made in my last post was much more realistic. But as usual, as with many threads, we start to over think them and forget the original question.
    2010 Kubota B26 TLB w/hyd thumb. 2004 John Deere X595 w/62" MMM.

    Carl Bertuzzi

  3. #73
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    Massey

    Default Re: What motor lasts longer

    Quote Originally Posted by Carl Bert View Post
    Did you ever think that you have the wrong mindset? It's like that joke where the wife calls the husband, on his way to work, and says "honey be careful, I just heard on the radio that there is some maniac driving the wrong way on the expressway". He says "there's not just one, there are hundreds of them".

    Your idea just isn't a fair comparison, you are not comparing two equal items. The engine must fit the task at hand. You're saying use a 40 HP diesel in place of where you would normally use a 400 HP. It just does not make sense. Obviously the motor will burn out prematurely, because you are not using it for what is was designed and built for. You would be overloading it and that would kill any engine.

    If you NEED to put a dollar value on the engines first, then it would have to go something like this. Purchase the recommended size diesel for the task at hand. Lets say its 250HP and costs $25,000. Now you have $25,000 to build a 250hp gas engine, which could now be built with much better quality materials than you would find in your average gas engine. Now you're comparing apples to apples. Run them both, under equal load, and see which lasts longer.

    Unfortunately we don't have the "better built gas engine" option in everyday life, so what's the sense. Thats why I think the comparison I made in my last post was much more realistic. But as usual, as with many threads, we start to over think them and forget the original question.
    I'd agree, if they were comperable but the reality is they are not. You don't go to a car showroom to buy a truck and get the option of picking a same diesl truck as a gas one, for the same money. That's because the diesel option for the vehicle was already designed as an expensive upgrade choice, and the manufacture'r already spec'd out a diesel that has more torque than their "normal" gas engine. So how is that a fair comparison?
    That's why you don't get to choose a fair vanella vs chocolate in a vehicle, becaue if you did have a real diesel or gas choice, they would have to put in such a puny little diesel, that little diesel would get worked much harder
    My point has if you had a fair comparison for options that were

  4. #74
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    Default Re: What motor lasts longer

    Quote Originally Posted by Carl Bert View Post
    Did you ever think that you have the wrong mindset? It's like that joke where the wife calls the husband, on his way to work, and says "honey be careful, I just heard on the radio that there is some maniac driving the wrong way on the expressway". He says "there's not just one, there are hundreds of them".

    Your idea just isn't a fair comparison, you are not comparing two equal items. The engine must fit the task at hand. You're saying use a 40 HP diesel in place of where you would normally use a 400 HP. It just does not make sense. Obviously the motor will burn out prematurely, because you are not using it for what is was designed and built for. You would be overloading it and that would kill any engine.

    If you NEED to put a dollar value on the engines first, then it would have to go something like this. Purchase the recommended size diesel for the task at hand. Lets say its 250HP and costs $25,000. Now you have $25,000 to build a 250hp gas engine, which could now be built with much better quality materials than you would find in your average gas engine. Now you're comparing apples to apples. Run them both, under equal load, and see which lasts longer.

    Unfortunately we don't have the "better built gas engine" option in everyday life, so what's the sense. Thats why I think the comparison I made in my last post was much more realistic. But as usual, as with many threads, we start to over think them and forget the original question.
    I'd agree, if they were comperable but the reality is they are not. You don't go to a car showroom to buy a truck and get the option of picking a same diesl truck as a gas one, for the same money. That's because the diesel option for the vehicle was already designed as an expensive upgrade choice, and the manufacture'r already spec'd out a diesel that has more torque than their "normal" gas engine. So how is that a fair comparison?
    That's why you don't get to choose a fair vanella vs chocolate in a vehicle, becaue if you did have a real diesel or gas choice, they would have to put in such a puny little diesel, that little diesel would get worked much harder.

    But for sure, if price, and weight are ignored, and you jsut go by displacement, the diesel will/should last longer. And I bring all this up, because the original post said " with all else being equal".

  5. #75
    Veteran Member MHarryE's Avatar
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    Okay, I have been attacked with statistics. Lets talk physics. Otto cycle (gasoline engine) vs. diesel cycle (diesel engine). The theoretical Otto cycle compresses an air/fuel mixture to a point where heat is added greatly increasing the pressure and therefore loads. In theory this occurs at TDC but of course it cannot be instantaneous but it is close. That pressure pushes the piston down in an is entropic expansion called the power stroke. At full power full load the stresses are quite high, but general automotive engine use has a very small percentage operation under full power. Most of the time the engine is running at part throttle. The optimum stoichiometric fuel air ratio is 14.6:1. Part throttle means closing off part of the air intake. It's like pinching your nostrils partly closed and trying to breathe. It gets harder. Same thing on a gasoline engine. The fuel/air ratio can't change much without causing per-ignition or overly rich mixture. So throttling reduces fuel economy. Limiting the compression ratio to limit per-ignition also hurts fuel economy.

    The diesel cycle has no throttling. The engine always gets a full gulp of air. Instead of all the heat being added at TDC, injection occurs over a period of time called constant pressure heating so in theory, the Diesel engine always sees the same pressure resulting in lower bearing load and is less than a gasoline engine running full power. The Diesel engine can run at a higher compression ratio because it depends on cylinder air temperature to light off the fuel instead of this pressure causing detonation. Pumping losses are minimized because there is no throttling in a diesel. There is no need to maintain a stoichiometric ratio like in a gasoline engine.

    Diesel engines are built beefier because they always see the maximum compression ratio as they are always taking in a full load of air each cycle no matter if they are at idle or full speed. Gasoline engines rated as having an 11:1 compression ratio see that ratio only at full power, wide open throttle. At freeway cruise the loads are way down as is the efficiency although the improvements made over the past decades like individual port injection, variable valve timing, etc. have greatly I proved efficiency over the gas guzzlers we had back in the 60's.

    If a gasoline engine was a long life design we would see them on the large marine engines that are on the oceans.

    Gasoline engines on the early tractors - low compression ratio due to poor fuel, and relatively low engine speed. Very simple carburetor. Poor fuel economy because they generally over fueled to prevent any chance of preignition.

    I said before I always prefer a diesel rental over a gasoline version, but a few times I have been on the Autostrade between Maranello and Milan, Italy, cruising at 200 km/hr and have had my doors blown off by some auto magazine type getting to test out the latest Ferrari. That is when I've wished I was in the gas engine car, but unfortunately the most any of those magazine testers have let me do is sit in the car and admire what you can own if you have big bucks. I don't think those engines last very long but then what is money to someone who can afford one.
    Last edited by MHarryE; 12-05-2012 at 01:43 AM.
    JD7720; KubotaM135GX; NH TS115A; JD6230; KubotaL5740

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