I found some nicely relevant specs (official) on these engines.
Check how flat the torque curves are on the non-turbo engines.
Here're the official (Isuzu) plots of the 4HK engines.
4HK1 engine
4HK1 engine
Official (Isuzu) plot of the 4HG1 engine
4HG1-T engine
Official (Isuzu) plot of the 4HF1 engine
4HF1 engine
Official (Isuzu) plot of the 4HE1T engine.
4HE1-T engine