I got into a discussion with a co-worker yesterday about tractors. He has quite a bit of land and mows with a standard lawn mower. I inevitably started lauding diesel CUT and SCUT tractors and how they were much more than just a lawn mower. I stated the usual about diesels and their much improved torque. I stated that my little 20HP diesel could do much more than a 20HP gas. Well he asked the simple little word "why".
I started trying to do some simple research to show him. To my surprise the huge differences that diesel owners are taught to believe don't seem to be there (anymore). Now before everyone starts flaming me, let me explain what I saw.. I also invite any proof the other way.
I started trying to just show some quick numbers to my coworker, so I grabbed some data from Kioti's site for my CK20's 21HP engine and tryed to find as close a gas engine as I could. I found a Kohler 20HP engine. I was flabbergasted. The torque was only 9ft/lb different. Well within the limits of the 1 HP true output difference. I compared a couple different engines. Some were slightly further apart. All favored the diesel... but none were huge. Only very slight. I started looking at some of the "scientific" sites and all seemed to corroborate what I had seen in the numbers. It seems that 95% of diesel engines torque advantage come from the tendency of diesel engines to have smaller bores but longer stroke than equivalent CC or CI gas engines. Not some magical property of simply being a diesel. In other words... create a gas engine with the same cubic inch, but in the same configuration (bore and stroke) and diesel torque is only VERY slightly better than gas. The remaining difference comes only from the higher compression of diesel which causes the torque curve to be different (not necessarily more) and the very slight more btu from diesel than gas.
So it seems that with todays newer (smaller) higher revving diesels, that yesterdays truth that diesels give tremendously more torque, is turning into todays partial myth. I guess it still holds true for big trucks with tremendously long strokes, but in the small diesels it seems it isn't as true. Many of the sites seem to say that with the advent of smaller, higher revving diesels, the "perceived" longevity of diesels as compared to gas will suffer as well. Longevity is a function of revolutions per work unit performed. Diesels have traditionally turned far fewer revolutions to perform the same amount of work, even that gap is narrowing because of the new short stroke diesels.
I started trying to do some simple research to show him. To my surprise the huge differences that diesel owners are taught to believe don't seem to be there (anymore). Now before everyone starts flaming me, let me explain what I saw.. I also invite any proof the other way.
I started trying to just show some quick numbers to my coworker, so I grabbed some data from Kioti's site for my CK20's 21HP engine and tryed to find as close a gas engine as I could. I found a Kohler 20HP engine. I was flabbergasted. The torque was only 9ft/lb different. Well within the limits of the 1 HP true output difference. I compared a couple different engines. Some were slightly further apart. All favored the diesel... but none were huge. Only very slight. I started looking at some of the "scientific" sites and all seemed to corroborate what I had seen in the numbers. It seems that 95% of diesel engines torque advantage come from the tendency of diesel engines to have smaller bores but longer stroke than equivalent CC or CI gas engines. Not some magical property of simply being a diesel. In other words... create a gas engine with the same cubic inch, but in the same configuration (bore and stroke) and diesel torque is only VERY slightly better than gas. The remaining difference comes only from the higher compression of diesel which causes the torque curve to be different (not necessarily more) and the very slight more btu from diesel than gas.
So it seems that with todays newer (smaller) higher revving diesels, that yesterdays truth that diesels give tremendously more torque, is turning into todays partial myth. I guess it still holds true for big trucks with tremendously long strokes, but in the small diesels it seems it isn't as true. Many of the sites seem to say that with the advent of smaller, higher revving diesels, the "perceived" longevity of diesels as compared to gas will suffer as well. Longevity is a function of revolutions per work unit performed. Diesels have traditionally turned far fewer revolutions to perform the same amount of work, even that gap is narrowing because of the new short stroke diesels.
