I think the later 1HZ made more power at the wheels from 2 things. Some settings in the injection system and the R151F gearbox that required less effort to spin than the old H55F.
A diesel injection specialist told me he dynos all of them after pump and or injector replacement. A new, recently run in 1HZ can attain 69-70hp. This drops off to about 65hp when they have 300000klms+ on the engine, but not all engines are the same due to driving and maintenance variations. I think he said my old cab chassis got about 67hp at 230000klms
He also said you can get another 7hp with a straight exhaust routing it down the left side and turning up the fuel slightly
A diesel injection specialist told me he dynos all of them after pump and or injector replacement. A new, recently run in 1HZ can attain 69-70hp. This drops off to about 65hp when they have 300000klms+ on the engine, but not all engines are the same due to driving and maintenance variations. I think he said my old cab chassis got about 67hp at 230000klms
He also said you can get another 7hp with a straight exhaust routing it down the left side and turning up the fuel slightly