HO vs SO 6.7 Cummins: Turbo Upgrade Differences (2019–2024)
One of the most common points of confusion for 2019–2024 6.7 Cummins owners is the difference between the High Output (HO) and Standard Output (SO) engines — and whether it changes how you should approach a turbo upgrade. It does, and understanding which truck you have makes the upgrade decision much clearer.
The two engines
Both engines run the same factory Holset HE300VG variable-geometry turbo, but they're tuned and paired very differently:
| Standard Output (SO) | High Output (HO) | |
|---|---|---|
| Trucks | Ram 2500 (and base 3500) | Ram 3500 only |
| Transmission | 68RFE | Aisin AS69RC |
| 2019–2020 rating | 370 hp / 850 lb-ft | 400 hp / 1,000 lb-ft |
| 2021–2024 rating | 370 hp / 850 lb-ft | 420 hp / 1,075 lb-ft |
The HO engine was the first diesel in its class to reach 1,000 lb-ft of torque, and the 2021 recalibration pushed it to 420 hp / 1,075 lb-ft, enabling max tow ratings around 37,100 lb on properly equipped 3500s. The SO engine held at 370 hp / 850 lb-ft across the range.
What it means for a turbo upgrade
Both engines benefit from the same core upgrade — more airflow and lower EGTs from a 63mm variable-geometry drop-in — but the emphasis shifts:
- HO / Aisin (Ram 3500): These trucks see the heaviest sustained loads and the highest factory torque. Controlling EGTs on long, heavy pulls is the priority, and the extra airflow of a 63mm HE300VG drop-in is most valuable here. Because the Aisin handles the torque, the goal is airflow and heat control, not chasing peak power.
- SO / 68RFE (Ram 2500): These trucks tow and daily-drive at lower factory output. The same drop-in improves spool response and airflow while keeping excellent street manners, and pairs well with sensible supporting mods.
Either way, the TNT HE300VG 63mm covers 2019–2024 applications and retains the factory VGT behaviour and exhaust brake. For how much the stock turbo can flow before it becomes the limit, see HE300VG Power Limits.
Which do I have?
If it's a Ram 2500, it's Standard Output with the 68RFE. If it's a Ram 3500 with the Aisin AS69RC, it's the High Output engine. When in doubt, your build sheet or VIN decode confirms it — and the Turbo Spec Form will match the right turbo either way.
Frequently asked questions
What's the difference between HO and SO 6.7 Cummins?
The HO (High Output) engine is exclusive to the Ram 3500 with the Aisin AS69RC transmission and is rated 400 hp / 1,000 lb-ft (2019–2020) or 420 hp / 1,075 lb-ft (2021–2024). The SO (Standard Output) engine runs in Ram 2500s with the 68RFE at 370 hp / 850 lb-ft.
Do HO and SO use the same turbo?
Yes — both use the factory Holset HE300VG, and both are covered by the 2019–2024 TNT HE300VG drop-in.
Is the HO engine worth upgrading if it already makes 420 hp?
The upgrade isn't about chasing peak numbers — it's airflow and lower EGTs for heavy, sustained towing, where the factory turbo works hardest.
Does the Aisin change the turbo upgrade?
No, but Aisin-equipped HO trucks tend to tow the heaviest, which is exactly where the extra airflow helps most with EGT control.