Volvo leans heavily into its Swedish roots, building hardy machines that can withstand brutal winters in its home country. Launched nearly a century ago, the Scandinavian automaker has made a name for itself as a bastion of car safety. After all, it was Volvo engineer Nils Bohlin who refined the three-point safety belt and shared the patent with the rest of the industry. With the 2025 XC90, the largest SUV in Volvo’s lineup, the brand has set the bar even higher with a refreshed version.
The XC90 is just in its second generation after two decades, which might be a sign of an outdated, tired model. However, Volvo has a few new tricks to keep the three-row SUV current, and this model year includes significant upgrades to the technology, standard suspension system, and the powertrain.
Everybody is talking about the sub-$40,000 Volvo EX30 EV, but the XC90 is far from over. With the 2025 model, it looks more like its all-electric EX90 sibling, bringing the family closer together. Plus, the 2025 XC90 includes a plug-in hybrid option that gets up to 37 miles of all-electric driving, an attractive option for those who aren’t ready to commit to an EV.
Miller Cycle boosts fuel efficiency
When it comes to modern engine history, you have to go way back to 1876, when German engineer Nicolaus Otto found a way to harness air induction and combustion to create power via compression. British engineer James Atkinson improved on this idea in 1882 with his four-stroke design, using a shorter and more efficient compression stroke.
Decades later, Ralph Miller patented the Miller-cycle engine in 1957 for even more efficiency. The simple genius behind the Miller cycle is that it leaves the intake valve open during part of the compression stroke. As a result, the engine squeezes against the pressure of the supercharger instead of the cylinder walls.
Volvo propulsion engineer Stefan Molen says that while the supercharger in the 2025 Volvo XC90 B5 and B6 models isn’t new, adding the Miller cycle makes it more efficient. “Updating the engine with the Miller cycle results in lower fuel consumption by four percent, which is quite a bit,” he says.
“The trick [of the Miller cycle] is allowing the intake valve to remain open for even longer and making up for the compression losses by using forced induction,” EngineLabs says. “By allowing the rising piston’s compression stroke to push air back into the intake manifold, the cylinder itself never reaches maximum capacity, but also reduces pumping losses.”
While this design may decrease performance figures at lower speeds, the explanation continues, ignition efficiency ratings spike significantly when that piston starts to drop. The result is a shorter intake stroke with less power and a complete downward “power stroke” for an improved compression process.
For the 2025 B5 model, for example, that translates to a two mpg improvement over 2024.
Frequency selective damping, explained
Ride comfort in the XC90 was never a low point. For 2025, the automaker has taken it up a notch with the new standard suspension in the gas-only B5 and B6 trim levels using Frequency Selective Damping technology.
“We took the standard suspension and raised the level,” says Volvo vehicle dynamics engineer Alessio Violin. “Basically, we delivered a new package of suspension tuning, which includes the springs, dampers, and anti-roll bars, and we changed the boost curve of the steering to match the response of the tires.”
By integrating an additional valve into the shock absorbers, the system controls a parallel oil flow alongside the primary flow through the piston assembly. When the valve arrests the parallel flow, the damping forces rise in correlation to the duration of one-way piston movement on the rebound side. By adjusting the rest of the suspension system, Volvo intends for passengers to feel, as a result, an even and balanced ride.
“The FSD valve makes the car more predictable, encouraging a high level of comfort,” Violin says. “FSD allows you to have freer wheels, which reduces vibration in the seats.”
The “frequency” part of FSD is not a frequency you can hear, Violin states. it’s a low frequency that affects the vehicle feel on the road.
“Let’s say you go over a small bump,” Violin explains. “Basically, on the compression side, it doesn’t do much, but on the rebound side it drops a little bit quicker and travels further away from the body. Over a series of small bumps, the wheels will follow the texture of the road.”
Driving across the nearly 10-mile Øresund Bridge between Denmark and Sweden, I noticed the difference in the gas-only model. However, if that’s not smooth enough for you, the plug-in hybrid is available with an even better air suspension, but you’re going to pay a premium: the XC90 T8 starts at $73,000.
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