thats the fun bit finding a engine that will give the torque needed at low enough revs.

a c15 could work in some applications as they are 500hp and prefer to work around 1300 rpm. the 2 stroke gm loved to work 1800 to 2100.
anything is possible if you can get or build reduction gearing and adapters suitably strong enough.

yes there's a ton of variables involved... its not totally about can i lug at 1200-1300 RPM is it??
-it seems many diesels are efficient in the 1800- 2000 RPM range....(not gospel)
doesn't HP = RPM x Torque divided by 5252?

yes thats the formula. these old girls did it by having large conrods so more torque for a given rpm.

the c series cats in trucks when coupled to a 18sp eaton trans they would work em between 1200 and 1800 always trying to maintain around 1300 to 1650 rpm the sweet spot around 1500

I like the large amounts of metal flying around comment!!!!!

-not sure if tons of metal flying around translates into more power at the flywheel...or a different kind of torque/ power delivered to finals etc....and more work done...?

-maybe some are totally underestimating what a 855 Cummins can do, ...work done per barrel etc... (Hint it not a slouch)

its all about leverage in essence a con rod is basically a big lever so the longer the lever the more force can be generated the larger the distance from crank centre to big end centre the more leverage so more torque as well.

yes you can have a engine that revs hard and make a lot of hp due to the rpm but it will be shit at shear pulling power because it doesn't have the torque.

where in the rev range a engine makes torque has a hell of a lot to do with how good it is at the task required. and to change that can be as simple as changing the camshaft.

The original post was to just repower something like a D8 with a smaller higher revving engine. How anyone would think a14 liter engine will handle producing enough horsepower and torque at much lower than its rated optimum revs and match 20 liters I am not sure. Those D342 engines are large, heavy and slow revving, an 855 Cummins needs to be running at much higher revs that do not match the gearing etc of a D8.

I have seen an old Ford V8 installed into an early D4, it made a lot of noise with lots of revs and just died when the load came on, had no hope in hell of matching what the old original slow revving engine did. If the question then becomes how many other modifications would have to be made to install a smaller high revving engine, what gearing etc would have to be fooled with, in the end why bother? Tractors fitted with smaller high revving engines are designed with gearing so that they work effectively..

I had a D8L that the governor and fuel settings got out of whack over time due to wear, revs went up, governor fuel dropped, they mismatched torque converter pressures, result wouldn't push the skin off a rice custard. It took about five hours to adjust it all to the top allowable settings, it then made the D9N running beside it to work harder to keep up, it obviously then needed the same treatment.

I always believed in the philosophy that if you are going to re power, use an identical or near identical engine to get best results. Just turning up fuel is not always the solution, I have had many Mack owners tell me an EM9400 will run with a E9500, that the 500 does not really gain much in a day pulling the same loads.
Wombat

Remember that guy south 40 ? I think he had a HT4 chassis he put various engines in whilst he left his original engine laying in pig slop? I think he had a Ford/cornbinder engine it it for a while.

close Wombat, but not quite...

-of course there is no way 14 litres can produce the power of 20 litres at the same RPM...the gearing would have to correct and it probably wouldn't be feasible to do that
-that's why i mentioned the HP formula, as far as i know 300 flywheel horsepower is 300 flywheel horsepower, no matter the cubic inches or strokes or RPM, or how you get there..

-a friend of my dad had several D7e and a D8 back in the 80s and 90s, then he switched to Komatsu 85, had 3 of them....he thought they were the greatest thing ever, that's where the 14L Cummins idea came from...