Could be out to lunch, but you can compare three different models with 19-19.5 PTO HP (540 RPM) but they are all at different engine RPM. For example the
BX2670 is at 3068 rpm, the
B2650 is at 2500 RPM, and the
L2501 is at 2105 RPM. If you convert those numbers into torque you'd end up with roughly 33.3 ft-lbs, 41 ft-lbs, and 48.6 ft-lbs, this is why the bigger displacement would or at least should run something like the stump grinder without bogging down as much.
Actually had a chance to use my BX42 wood
chipper on both my previous
B2650 as well as a friends
BX25D, it was quite surprising the difference in how fast the smaller BX engine would bog down or stall compared to the
B2650, there would likely be a similar difference between a
L2501 and a
B2650 as well.