Why do cars have a “power range”


I know a decent bit about cars, but it is still a mystery to me why cars have more power at some points in their rev range than other parts of it. For example I’m told that diesel engines are really powerful at low revs and small displacement engines need to be revved higher to have power. Why is this?

In: Engineering

Power output of engines is proportional to engine RPM and torque and torque depends on engine size, geometry, compression ratio, and a few other factors. Put simple higher RPM = more power, but smaller engine= less power, ergo small engine needs to rev up to put out as much power while diesel with higher compression ratios create more power at less RPM.

In general ICE only create enough torque in a very narrow band of RPM, that is the ‘power range’. More RPMs and any gained power is lost as waste heat, fewer RPMs and you aren’t creating enough power to turn turn the motor over. At the low end you are dedicating too much power to turn the motor that the propshaft won’t turn.

Very simplified. And on mobile so sorry about formatting.

Various factors change where the power curves lie. Displacement, fuel type, induction, cylinder layout, fuel delivery system, even tuning.

A cride example. Aus Ford’s inline 6 petrol vs Aus Toyotas 1hz. They are both inline 6’s similar enough displacement. The 1hz is a diesel makes very little hp and good torque, but makes it all down low. The ford’s motor makes better hp some models similar torque but makes it at much higher rpm.