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High Bottom end torque and RPM limiting perspectives ... - Rawze - 08-07-2021
(High Bottom end torque and RPM limiting perspectives) …
The ISX Diesel engines as a whole do not like low RPM torque at all. If an ISX engine has been programmed, geared, or otherwise restricted to mostly only operate below 1500 RPM (many fleet trucks are like this), it is very hard on one. Instead of using a higher, more proper RPM and better gearing to get more power from their truck, people tend to want to always raise torque output at low rpm ranges instead. The ISX is well capable of producing high torque at low RPM’s but this does not mean it is good for them at all. The higher the low-end torque an ISX has, the shorter its overall lifespan will be. The lifespan changes significantly.
Many fleet-spec’d trucks are set to be governed so that they will not go above 1500 RPM. This is done as an artificial way to control the drivers right foot for forced fuel mileage savings (an entire conversation in of itself). This is VERY HARD ON THE ENGINE AND SHORTENS ITS OVERALL LIFESPAN!. Here is what is typically seen on trucks that endure medium-to-heavy operations, the RPM has been limited, and higher torque at low RPM ranges is used to make up for the truck not wanting to produce its full power ...
* At 1650 ft-lbs torque, lifespan is easily around 1+Million miles ( or ~25,000 hours ) before the head has to come off it for one reason or another.
* At 1750 ft-lbs torque, lifespan is usually around 900k - 1+Million miles ( or ~22,000 hours ) before the head has to come off it for one reason or another.
* At 1850 ft-lbs torque, lifespan is usually around 650k - 700k miles ( or ~16,000 hours ) before the head has to come off it for one reason or another.
* At 2050 ft-lbs torque, lifespan is usually around 550k miles ( or 13,000 hours ) before the head has to come off it for one reason or another.
Any trucks that make a lot of use of PTO operations in low RPM ranges suffer greatly too. Many of these setups are geared so that the engine only turns 1,000 RPM or so under load. This is real bad. This is also due to high torque and very low RPM use. This includes Pump vac trucks, car-haulers, bulk tank haulers with their own on-board pumping units, and other trucks with hydraulic PTO units. It is not unusual at all to see, say a car-hauler truck, only last 450k miles before the engine is toast. - ALL of this shortened engine life can be prevented through better use and better gearing... and better gearing of any PTO units.
- Despite what the engine maker claims, as can be seen above, the difference between 1650 ft.lbs and 2050 ft.lbs, the engine lifespan is easily cut in HALF, depending on its use and operations. If someone wants more power, it should be done BY WAY OF HIGHER RPM RANGES and not by increasing torque… especially bottom end torque. This means that Literally … an ISX that is set for 600HP/1750 ft.lbs torque will far outlast an ISX engine set at 500HP/2050 ft.lbs.
It is the TORQUE that shortens the lifespan… NOT THE Horsepower!.
- Every truck experiences different load applications so the numbers are higher or lower depending on how the truck was driven.. but those are the general trends that have been seen on the forum here for the last several years of helping others.
If someone wants to improve engine life... GEAR THE TRUCK PROPERLY for its intended operations so that higher RPM ranges can be used to make power.. STOP trying to torture your engine and drive-train by making a lot of torque against an improperly geared, fleet-spec'd truck.
RE: High Bottom end torque and RPM limiting perspectives ... - KW660_16 - 08-07-2021
I agree. I can't stand these new engines that don't rev over 1500. My truck revs whatever I tell it to, and gets great power as its operating in it's peak rpm power band.