Test Drive Review: The 2014 Mercedes-Benz GL450 – Part 4 (Powertrain)

Review Index:
The 2014 Mercedes-Benz GL450 – Part 1 (Exterior)
The 2014 Mercedes-Benz GL450 – Part 2 (Interior)
The 2014 Mercedes-Benz GL450 – Part 3 (Chassis and Suspension)
The 2014 Mercedes-Benz GL450 – Part 4 (Powertrain)

The GL450 is equipped with Mercedes-Benz’s M278 engine.

The M278 is Mercedes-Benz’s latest direct injected, twin-turbocharged V8 engine, with 4.7L displacement. Basically speaking, M278 is the turbo version of the M273 V8, plus fuel direct injection. This same engine can be seen on many Mercedes-Benz vehicles such as the S-class, CL-class, CLS-class, E-class, M-class etc, but with different tunes to generate different level of outputs. The version used on the GL450 has 362hp and 406 lb-ft of torque.


The M278 engine is mated to the brand’s unified 7G-Tronic transmission. By its name “7G”, it means 7-speed. Unlike its application on Mercedes sedans, which uses the 2nd gear as the starting gear in acceleration from a standstill (unless you put the selection in “Sport” mode), it uses the 1st gear as a starting point. The reason for this is because of GL450’s heavy weight. Mercedes-Benz claims its curb weight to be 5,401 lbs, however our test show that it is close to 6,000 lbs on the scale with one person (the driver) sitting in the car. The V8 cannot provide enough torque while using 2nd gear to move the car, and anyway there is no power mode (normal/sport) to choose from on our test car, so all the throttle mapping and transmission shifting pattern are control by the ECU, you cannot do anything about this.

For daily driving, the turbocharged V8 provides satisfactory power; especially when you want to do a quick passing on the highway, task can be done effortless usually with engine RPM not exceeding 3,000 RPM. However, turbo lag caused a “slow” feeling when you are in stop-and-go traffic: sometimes you need to rev the RPM up to 4,000 RPM to keep up with the traffic. However, situation described here fully depends on people’s driving style locally. If you think in your neighborhood, people normally drive like in southern California, then my comments above can be a reference for you.

On uphill section of I-5 near the Frazier Mountain area, the GL450 need to shift down to the 5th gear to keep a 70mph cruising speed. While we understand the GL-class is a heavy SUV, we expect the turbocharged V8 should have enough torque to do better.

With the V8 engine in the engine bay, area under the hood is fully packed. From the below photo you can see there is no extra space for a larger engine such as a V12. So there is no chance to see a V12 AMG version for the GL-class, for example a GL65 AMG. It won’t exist.


You may also find that like some high-performance sports car, there are two large vents on the GL’s engine hood. But their purpose is not as what you think. The vent on the passenger side, is air intake for the cabin AC system; and the one on the driver side, is a fake one – it is not functional at all, only one small holes under it to drain the water in the rainy days.


Here is the engine sticker under the hood.


The GL-class rides on a rear-wheel-drive platform, you can see in the below image that, the engine sits on the front axle and is located as backward as possible. This provides a good front/rear weight distribution ratio, but the downside is this takes up some cabin spaces, especially the legroom. You see, the GL-class has a considerably-long wheelbase of 121.1-in, but from our live photo in this review series, the legroom of the second row and third row seats are not so spacious at all.


Mercedes-Benz pays much attention on the cabin quietness aspect. For example, very thick sound insulation materials can be seen in the engine compartment, especially in the strut tower and firewall area, as can be seen in the below photo.


Generally speaking, the GL450’s powertrain is OK from my point of view. Before closing our test drive review here, I want to mention the upper trim of GL-class: the GL550. MSRP for the 2014 GL550 is $88,600, and the 2014 GL450 is $64,500.

Taking into consideration that some optional features on GL450 is standard on GL550 (for example several packages, leather seats, 3-zone ACs etc.), there is still a $10,575 price gap which can only be explained by the different engine output. But the fact is: mechanically speaking, the engines are identical on GL450 and GL550, they just have different ECU software running, which raises GL550’s turbo boost pressure, therefore making higher output. Are you willing to pay a five-digit price for a different software? There is no definite answer, please use your own judgement to make decision.


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