Eli5: how do some cars with turbos max out their torque and horsepower at a low rpm?

Question

My car has a turbo, and it makes max torque and horsepower at 2k rpm and drops off from there. In theory, shouldn’t the higher the rpm’s are mean more torque and horsepower with more air going through the turbo?

In: 4

Answer 1

Higher RPMs does mean more air going through the turbo but doesn’t necessarily mean more boost (which would give you more torque, all other things being equal). Going higher RPM than that means more pumping loses (work to move air through the system), less time for combustion, more friction losses, etc. This is why the power always rolls off eventually, the gain in RPM isn’t enough to offset the loss in torque (true for turbos or non).

2k RPM seems low unless you’re talking about a big diesel though.