Cummins QSB5G1 vs Isuzu 4JJ1X
The Cummins QSB5G1 and Isuzu 4JJ1X are both diesel generator engines in a similar power class. Both are rated at roughly 71 kVA. Displacement is 4.5 L versus 2.999 L. The table below compares their full specifications side by side.
| Specification | Cummins QSB5G1 | Isuzu 4JJ1X |
|---|---|---|
| Headline rating | 70 kVA | 71 kVA |
| Standby (50 Hz) | 56 kWe | 56.4 kWe |
| Prime (50 Hz) | 50 kWe | 51.3 kWe |
| Standby (60 Hz) | 60 kWe | 70.3 kWe |
| Prime (60 Hz) | 55 kWe | 63.9 kWe |
| Displacement | 4.5 L | 2.999 L |
| Configuration | L4 | L4 |
| Cylinders | 4 | 4 |
| Rated speed | 1,500 / 1,800 RPM | 1,500 / 1,800 RPM |
| Fuel | Diesel | Diesel |
| Cooling | Liquid-Cooled | Liquid-Cooled |
| Emissions | U.S. EPA Tier 3 / EU Stage IIIA / China III | U.S. EPA Final Tier 4 |
| Dry weight | — | — |
| Origin | United States / United Kingdom | Japan |
Choosing between Cummins QSB5G1 and Isuzu 4JJ1X
Use this comparison as an engineering shortlist, then confirm the complete generator package against load profile, voltage, 50/60 Hz frequency, duty class, emissions rules, cooling margin, altitude, ambient temperature, enclosure design, controller features, and alternator sizing. The Isuzu 4JJ1X has the higher headline kVA rating in this pair, but site conditions and duty cycle can still change the final recommendation.