Its all apples and oranges for the most part. You run an engine the way it was designed to be run and it lasts. Big diesels like Cats, Cummins, Detroit, etc are slow engines because the weight of the recipricating parts demand that they be slow engines. More than one idiot driver while I was in the service thought he/she (yeah had two females do it) would be slick and turn the governers up on their trucks, only to have bearings fail and more than one even toss a rod through the block, the gold star goes to the idiot who turned it up 1000 rpm on a 10 ton powered by a v-8 mack, put a piston through the cylinder head at 2,600 rpm according to the tachograph. governed rpm was supposed to 1,900 rpm. These are big bore long stroke engines. The rods are heavy, and the pistons weigh a ton. The bore and stroke in a Detroit Series 60 11ltr is
5.12 X 5.47 inches, The series 55 12 ltr has a 5.04 X 6.10 . You start getting into the stationary, marine, or train engines and you get 2 or 4ltrs per cylinder in 8V, 12V, or 16V configs. The Cat C15 is 5.4 X 6.75 inches,
928 cubic inches inline 6 cylinder (15.2ltrs) 550 hp at 2100 rpm, 1850 lb-ft of torque at 1200 rpm. Drop down the the C11 (11.1 ltr) and the numbers drop to 5.12 X 5.51, hp down to 370, and torque 1450. My old Kenworth T-600 with a cummins NT-14 435e could keep up with anything bob tail, and embarrased more than a few guys in cars off the line, and never turned more than 2,100 rpm.
compare this to the duramax 7800 7.8 ltr inline 6 engine with a bore and stroke of 4.53 X 4.92 200 hp, 520 lb ft of torque at 2,200 rpm, or the duramax 6.6 V-8 with 4.05 X 3.89 inches 310 hp at 3,500 rpm and 605 at
1,600 rpm. The rpms have gone up, the bore and stroke have gotten smaller, the parts weigh a lot less. Get to the 8100 V-8 4.25 X 4.37inches and our rpms are over 4,000 for hp, and over 3,000 rpm for peak torque..
course the Duramax weighs about 1/3 what a cummins NT-14 435E, or Cat C11, or Detroit Series 60 11 ltr weigh. The fact is heavy parts dont handle high rpm and stay together, coupled with heavy parts store a lot of energy when they are moving. There is a reason those old exposed flywheel engines had such large flywheels compared to their displacement. You take a light duty truck engine, gear it to keep the rpm down and try pulling a load, it wont get out of its own weigh, and wont last very long ether. Same token gear it too high and you'll burn the engine up. Ever notice how the old inline 6 engines always had a larger diameter and heavier fly wheel than the small block V-8s did?
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