There’s been confusion about why Ram put big 3.6 liter V6 as a range extender on the 2025 Ramcahrger. Surely that is terribly inefficient?

No, it’s not.

Ram states following specs: 92kWh battery pack, 145 miles of electric range and 690 miles of total range, 27 gallon gas tank.

Electric range of 145 miles with 92 kWh means electricity consumption of 63 kWh/100 miles. Full tank contains 920 kWh of energy and gives 545 miles of range. That is consumption of 168 kWh/100 miles. The electric energy needed for 545 miles is 343 kWh, so the efficiency of the range extender is 37%. The generator and electronics have some energy loss so the efficiency of the V6 engine is closer to 40%. That’s crazy efficient for a gas engine.

Why is it so high? Why not use smaller engine?

Engine efficiency is highest at relatively slow speed and nearly full load. That big V6 can produce the required power at low RPM but needs to work hard. That’s very efficient. Smaller engine would need to run very fast which decreases efficiency.

In summary the V6 is very efficient at this particular application which suits it very well.