Ford, the company that only sells its compact Ranger with a four-cylinder and whose flagship F-150 engine is a twin-turbo V6, has created a new 7.3-liter V-8. With pushrods. And the company's engineers did it for fuel economy.
This might seem odd to you. After all, the pushrod V-8 is one of the oldest engine designs in the business-Ford started building them in the early 1930s. And while GM and Fiat Chrysler have continually offered gas-powered pushrod V-8s, outside of crate motors, Ford phased them out around 20 years ago. Until the 2020 Super Duty debuted last week, the only new pushrod V-8 Ford offered in a production vehicle was the 6.7-liter Power Stroke diesel.
A new pushrod V-8, let alone one displacing a hearty 7.3 liters, might seem backwards to you. But it isn't. We talked to Joel Beltramo, manager for V-8 gas engines at Ford, about why a big pushrod motor makes sense here.
Beltramo pointed out that most vehicles with a gross vehicle weight rating (GVWR) of under 8500 pounds cruise around without carrying or towing much weight at all. That means they don't use much sustained horsepower. By contrast, vehicles with a GVWR over 8500 pounds tend to tow and haul a lot, which means they're using a lot of their horsepower a lot of the time.
In vehicles with 14,000-plus-pound GVWRs-like the Ford Super Duty-Beltramo told us its critical for an engine to operate at peak power with an optimal air-fuel ratio (stoichiometric efficiency). From there, Ford worked backwards.
"We built a map of where an engine, can run stoichiometric air-fuel without a bunch of spark retard," Beltramo said. "That led us to a torque-per-liter value and a power-per-liter value, [which] knowing that, boxed us to 7.3 liters."
For fuel efficiency's sake, Ford engineers determined they wanted the engine to generate peak power at what Beltramo considers "relatively low" RPMs. "That's what led us to a pushrod two-valve. It really is the optimum solution for the over 14,000-pound [segment]."
Typically, a pushrod engine makes lots of torque at low RPMs, while an overhead-cam engine-like the 5.0-liter Coyote in the Mustang-does its best work from the middle to the top of the rev range. When towing/hauling a big load, a truck's engine needs to be making peak power, and if it's doing so at relatively low RPMs, it won't use a ton of gas
"If you used [the 7.3-liter] in an F-150 or something, it would not return the kind of fuel economy at light load as some of our other engine offerings that we deploy in that vehicle," Beltramo said. "There would be a hit for the displacement. But when you start talking about running day-in day-out, at high weights...the displacement brings a big fuel-economy benefit."
Ford thinks there'll be other benefits brought by the 7.3. For one, it'll be cheaper than the 6.7-liter Power Stroke diesel V8, which should appeal to fleet buyers, and to those in areas where gas prices are especially cheap (fuel economy for the diesel should still be better, though Ford doesn't have numbers). Then there's serviceability-in a number of ways, the 7.3 is similar to the 6.7-liter Power Stroke, so technicians won't have a totally new engine they'll need to learn.
This 7.3-liter should be pretty durable, too, thanks to a cast-iron block, a forged steel crankshaft, and oil jets to cool the pistons. Generally speaking, pushrod engines are a lot simpler than their overhead-cam counterparts, so there's a lot less stuff to break.
There's also the relative compactness of an engine without overhead camshafts. Beltramo said the 7.3-liter is quite a bit shorter in height than the 6.8-liter overhead-cam V-8 it replaces, and not too different in any other dimension. This compactness means there'll be lots of room in the engine bays in which the 7.3-liter finds a home, which Beltramo said helps with cooling.
And if you're wondering if it'll fit in a Mustang, Beltramo told us it's actually shorter in height and narrower than a Coyote V-8, but quite a bit longer thanks to much increased bore centers. It's possible then, but good luck doing so without having to cut into the firewall. And even if you could wedge this motor into a Mustang, it wouldn't be very good, because of its heavy cast iron block and low-revving nature. Stick with the Coyote, kids.
Beltramo said that there aren't any plans on sticking this engine in an F-150 either, but it will eventually find a home in medium-duty trucks like the F-650 and F-750.
The transmission it's paired to isn't old-school, either. It's Ford's now-familiar 10-speed, though one that's been optimized for big truck usage. It should help boost fuel-economy, too.
Automakers talk about fuel-economy and how it impacts engine design a lot, but what's interesting here is that at least in the US, trucks like the Super Duty don't have any standards to meet. The EPA doesn't require automakers to report fuel-economy figures for pickups with a GWVR of over 8500 pounds, so these trucks can be as efficient or inefficient as the automakers like.
Therefore, when Ford chases increased fuel economy for a truck like the Super Duty, it's just to improve real-world results. In vehicles where fuel economy is reported, automakers have turned to downsized, turbocharged engines to get achieve better MPG figures in lab testing-sometimes at the expense of real-world fuel economy.
It's funny that when automakers have to perform standardized fuel-economy testing, they started making more small, turbo motors. But when Ford tried to get better real-world fuel economy in its bigger trucks, it came up with a big honking V-8.
It makes perfect sense.
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