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The 1.8-liter four-cylinder engine used in the Prius generates 98 horsepower. Combined with the electric motors, there's a total of 134 horsepower.
The Hybrid Synergy Drive system, with two compact motor generators within the transaxle, delivers operating voltage of 650 volts. It uses gear drive, allowing the motor to turn 13,500 rpm. The Power Control Unit (inverter) is compact. The Nickel-Metal Hydride battery pack is compact and powerful. The Lithium Ion setup in the Plug-in Hybrid weighs a little more. The air conditioning compressor and water pump are driven electrically, which means the air conditioner works, though not full blast, even with the engine turned off.
There are three driving modes: EV, or all-electric, with a very limited distance at 25 mph or less (if there's enough juice in the battery), most useful for underground parking garages.
That's the advantage of the Prius Plug-in Hybrid. It can run at speeds of up to 62 mph in EV mode for up to 15 miles, great for stop-and-go commuting.
ECO mode minimizes fuel consumption by reducing the throttle opening and restricting the air conditioning. The Power mode is for maximum acceleration performance. The difference between Power and ECO is 4.1 seconds from 50 to 70 mph, versus 5.8 seconds. If you're in ECO and floor it, it will kick itself into Power, which is also the default mode when you start it up. So you have to set ECO mode at every stop, to get the best mileage. But we wonder why anyone would drive around town in Power mode, because ECO feels no slower. The Prius accelerates from 0 to 60 mph in 9.8 seconds, usually fast enough though slow by modern standards.
When you accelerate hard and it kicks into Power mode, it can be abrupt, like a transmission kick-down. But like all hybrids it uses a CVT, continuously variable transmission, which is technically not an automatic because it doesn't have gears. Most of the time you're not aware the Prius CVT is there, which is how they're supposed to work.
The Prius is EPA-rated at 51 city and 48 highway, for a combined 50 miles per gallon. We got 54 mpg driving gently but still sometimes using Power mode, over 23 miles of city-highway driving; and later 70.5 mpg over a 34-mile street course in a competition with other automotive journalists. We averaged 28 mph, about average for the group.
The winner, a specialist hypermiler, got 94.6 mpg driving by all the tricks. He averaged 19 mph, moving at about 30 mph in the far right emergency lane of the 50-mph highway, showing that it takes travel in an unreal world to achieve those big numbers. That sort of driving affects the driving behavior of others and reduces the fuel efficiency of others. An opposite leadfoot extremist managed to get 26.8 mpg. The other 26 of 28 drivers got between 63.3 and 75.3 mpg.
In an early prototype of the Plug-in Hybrid, we got 41.8 mpg for about 180 miles, 26 of them on full electric, and most of the rest at 65-70 mpg in Power mode.
Ride quality is far from stellar in the Prius Liftback. It's pretty rough over patchy roads, and we noticed a lot of road noise. A test drive in the Prius Plug-in Hybrid, however, felt somewhat smoother. Still, we didn't think it behaved as well as the Ford C-Max plug-in.
We also drove a Prius with the optional 17-inch wheels and 215/45R17 tires, which felt slightly smoother although theoretically they should be firmer; we got better mileage with them, 57.4 mpg, although the Prius chief engineer said the 17s deliver about 5-percent less mileage.
The four-wheel disc brakes are sensitive, and we could hear rubbing at low speeds with ours, partly because there was no engine noise when backing off, and possibly because of the regenerative braking component: the more you use the brakes, the more battery juice you build up, enabling you to use EV mode more. On our 70.5-mpg run, we gently used the brakes a lot in city traffic, so we would get as many blocks as possible out of EV mode.
The handling is light enough around town, but out on the road, if you try to drive it aggressively in corners, it turns heavy and slow. The slower you drive it, the better it is. That said, cornering is much improved over pre-2010 models with the redesigned chassis and suspension.
We also tested the optional Intelligent Parking Assist, which parallel parks the car for you, if the space is big enough. It worked well, the system requires a margin of 7 feet 9 inches, which won't help if you're trying to fit into a tight spot.