Ford’s new SuperDuty diesel pumps up power
THERE is a power race going on in the truck world, and Ford has upped the stakes again with the 2015 SuperDuty 6.7 diesel engine.
There are several changes to the engine to give it more power and torque, which in the work world where these trucks are used for towing or hauling loads means they are even more capable.
In the last decade, Ford’s SuperDuty diesel has gone from 325 horsepower and 570 foot-pounds of torque to the current 440 horsepower and 860 footpounds of torque. Along with other changes to frame, transmission, axles and suspension over the years, the 2015 model has increased towing capacity to an incredible 31,200 pounds for fifth-wheel trailers. This is close to what semi trucks were hauling only a few years ago on the road, and the SuperDuty does it with style and comfort you could never find in a semi.
So what gives the 2015 engine so much power? It is a combination of many things, but let’s start with the turbo. The turbo is now larger for more airflow, but it also has been changed to a variable-vane design and eliminated the waste-gate. Variable vane turbochargers use small vanes, that can have the angle change that they sit at. As the angle changes, the exhaust gases are directed more or less at the turbocharger wheel to control engine boost. The results are more powerful boost at low rpm.
The SuperDuty takes advantage of the variable-vane turbo in another way, by using the vanes to provide engine braking on downhill grades. A button on the dash turns on the engine braking, and the computer will operate the vanes so the exhaust gas flow is restricted. On long, downhill grades, especially when towing, this can take a lot of load off the vehicle brakes and makes for safer towing.
The cylinder heads and exhaust manifolds have also been changed to allow for more airflow. Increasing airflow is what allows for the biggest increase in power, but to get more power, you also need to be able to provide more fuel. New fuel injectors and high-volume fuel systems deliver that fuel when you need the power, but Ford claims the engine is also more fuel-efficient than last year’s model.
One of the keys to maintaining peak power on any engine is cooling. If the cooling system is limited, so is the amount of power that can be continually produced. The SuperDuty uses two completely separate cooling systems. Both systems are completely separate, with their own radiators and engine-driven water pumps. The main cooling system has a 27.8-U.S.-quart capacity and cools the engine block, cylinder head, engine oil and exhaust gas recirculation system.
The secondary cooling system has an 11-U.S.-quart capacity and is used to cool the fuel, transmission oil and the air to a liquid intercooler that cools the intake air. In this system, the fuel cooler uses about one per cent of the cooling, the transmission oil uses about 10 per cent of the cooling and the intercooler uses nearly 90 per cent of the cooling. The radiator for this system is a two-pass design, which means the coolant flows through the top half and then flows back through the bottom half. This design provides a longer time for the coolant to be cooled by the passing air and is more efficient. The transmission-oil cooler draws coolant from the midpoint of the radiator (after the first pass) and the temperature of the coolant increases from about 30 degrees C to about 45 degrees C before returning to the radiator. The intercooler takes coolant after the second pass and the 30 C coolant heats to about 60 C as it passes through the intercooler. Thermostats on both these systems reduce the coolant flow when coolant temperatures are low.
The cooling system is integral to long-term reliability and power, so although it may seem a bit complicated, separating the engine cooling from the intercooler and transmission cooling makes a lot of sense.
Whenever an engine is designed for more power, other parts should also be upgraded. The six-speed automatic transmission may look similar, but internally, it has a new torque converter and internal mechanical parts to handle the increased power. This is the same transmission Ford will use in the new F550 and F650 series trucks, so the SuperDuty really is built for heavy-duty capability.