Cummins ISX12G 320
Built: 2013 · Series: ISX12G
More machines from model year 2013
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Cummins ISX12 G — the Predecessor of Today's Cummins Gas Engines – inline six-cylinder natural-gas engine of 11.9 litres, 320 to 400 hp, for heavy tractors and distribution trucks
The Cummins Westport ISX12 G is an inline six-cylinder natural-gas engine of 11.9 litres, running exclusively on natural gas as either CNG or LNG. Combustion uses Cummins Westport's stoichiometric, cooled-EGR (SEGR) technology with spark ignition; aftertreatment is a maintenance-free three-way catalyst packaged as a muffler. Depending on rating, output spans 320 to 400 hp (239–298 kW) with up to 1,450 lb-ft (1,966 N·m) of torque.
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From 2013 the ISX12 G expanded Cummins' heavy-duty on-highway natural-gas range and has since been fully superseded by the ISX12N, which meets stricter near-zero emission limits.
Applications included heavy tractors and distribution trucks, notably at Kenworth; ratings on record include ISX12G 320, 330, 350, 385 and 400.
As a stoichiometric, spark-ignited gas engine, the ISX12 G follows the Otto-cycle principle rather than a diesel's compression ignition; its design is governed by the knock limit of the homogeneous natural-gas/air mixture, so specific output per litre is naturally lower than a comparable diesel. Unlike diesel tractors, natural-gas trucks are tied to CNG or LNG filling stations and therefore suit distribution and regional haulage with planned routes rather than open long-haul work.
As the engine is no longer sold new, parts availability is the main practical concern for used units, alongside the original two-year/250,000-mile factory warranty framework as a benchmark for design intent; no further type-specific weak points are documented in the sources reviewed.
Sources: SpecCodex register, model data: Cummins ISX12G, Cummins (manufacturer)
Technical data
Engine
| Engine code | 3647; FR20300correct |
|---|---|
| Engine family | DCEXH0729XBAcorrect |
| Engine families | DCEXH0729XBAcorrect |
| Fuel | Natural Gascorrect |
| Rated output | 238.6 kW (= 320 bhp)correct |
| Rated speed | 1,700 rpmcorrect |
| Maximum torque | 1,150 ft·lbfcorrect |
| Speed at max. torque | 1,200 rpmcorrect |
| Operating cycle | dieselcorrect |
| Injection | throttle-body injectioncorrect |
| Aspiration | single-stage turbocorrect |
Origin and approval
| Built from | 2013correct |
|---|---|
| Built to | 2013correct |
| Model year from | 2013correct |
| Model year to | 2013correct |
Other data
| Application | HHDDcorrect |
|---|
Frequently asked questions
How much power does the Cummins ISX12G 320 have?
The Cummins ISX12G 320 delivers 239 kW.
When was the Cummins ISX12G 320 built?
Production years: 2013.
What to check before buying
- Match the data plate against the order: frame size, mounting and rating have to agree.
- For used units, ask about winding condition and bearing play.
- Ask about parts availability for this series — the running costs hang on it.
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This page carries 19 individual figures for this model. They come from 1 recorded source; every figure can be traced there. What we cannot document is not here — we leave gaps open rather than estimate them.
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Sources: US EPA — engine certification data (retrieved August 2026) · How we check the data
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