The primary difference between the EMD GP38-2 and the EMD GP39-2 lies in their engine configurations and resulting horsepower, which in turn affects their performance characteristics and operational economy.
Understanding the Key Distinctions
Both the GP38-2 and GP39-2 are four-axle, Bo-Bo road switcher locomotives from Electro-Motive Diesel (EMD) and belong to the "Dash-2" series, introduced in 1972. The "Dash-2" line signified improved modular electronic control systems and other upgrades over their predecessors. However, their core power plants define their distinct roles and capabilities.
Engine and Horsepower
The most significant divergence between these two popular locomotive models is their prime mover:
- GP38-2: This model is equipped with a 16-cylinder EMD 645E engine that is naturally aspirated. This means it does not use a turbocharger to force more air into the engine. As a result, the GP38-2 produces 2,000 horsepower. Its naturally aspirated design contributes to its reputation for robust reliability and simpler maintenance.
- GP39-2: In contrast, the GP39-2 features a 12-cylinder EMD 645E3 engine that is turbocharged. The turbocharger increases the engine's efficiency by forcing more air into the cylinders, allowing for a higher power output from a smaller displacement. This configuration enables the GP39-2 to generate 2,300 horsepower, a 300 hp advantage over the GP38-2.
Operational Performance and Market Niche
While the original GP39 had limited sales due to railroads' preference for the reliable, non-turbocharged GP38, the GP39-2 found considerable success. This success, especially noticeable during the 1970s energy crisis, was largely attributed to two key advantages over the GP38-2:
- Better Fuel Economy: The turbocharged 12-cylinder engine of the GP39-2, despite its higher horsepower, proved to be more fuel-efficient than the naturally aspirated 16-cylinder engine of the GP38-2. This became a critical factor for railroads facing escalating fuel costs.
- Enhanced Performance at Altitude: Turbocharged engines perform better at higher altitudes compared to naturally aspirated engines. As air density decreases with elevation, naturally aspirated engines lose power. A turbocharger compensates for this by compressing the thinner air, allowing the engine to maintain more of its sea-level power output, making the GP39-2 a more suitable choice for operations in mountainous regions.
Summary of Differences
| Feature | EMD GP38-2 | EMD GP39-2 |
|---|---|---|
| Engine Type | 16-cylinder EMD 645E | 12-cylinder EMD 645E3 |
| Aspiration | Naturally Aspirated | Turbocharged |
| Horsepower | 2,000 hp | 2,300 hp |
| Fuel Economy | Generally less fuel-efficient than GP39-2 | Generally better fuel economy than GP38-2 |
| Altitude Perf. | Power output decreases significantly at altitude | Maintains better performance at higher altitudes |
| Maintenance | Simpler due to fewer components (no turbo) | Slightly more complex due to turbocharger |
| Primary Advantage | Reliability, simpler design, lower initial cost | Higher power, better fuel economy, altitude performance |
In essence, the GP38-2 represents a simpler, robust, and reliable workhorse ideal for general switching and lighter road service where maximum power or fuel efficiency are not paramount. The GP39-2, with its turbocharged engine, offers a compelling balance of higher power, improved fuel economy, and better high-altitude performance, making it an economically attractive option for railroads, particularly during periods of high energy costs.
