Would You Buy a Performance Hybrid?
I took to the 2013 Jetta Hybrid at the Baltimore Auto Show. Even though I knew it cost more than I want to spend on a car, I was daydreaming and rationalizing the arguments for buying one. But my research is telling me that it was just a schoolboy crush.
First, an online review pointed out that VDub recommends premium fuel for the Jetta Hybrid. I assumed high octane was a requirement for running a turbocharged engine. Turbos save engine weight, can save fuel, and have become very common in small cars, but the idea of paying more for gas seemed at cross-purposes to the idea of saving money by purchasing a hybrid with 42/48 mpg. Then I read several reviews that criticised the inconsistent feel of the Jetta’s regenerative braking. Then Green Car Reports took a second test drive:
During the course of a week, we drove 114 miles at an average speed of 20 mph. Disappointingly, our average fuel economy was 34.8 mpg. In fact, we never once saw an average number anywhere near 40 mpg.
So where’s the fuel efficiency from that turbo? Well, a CNET review from December 2012 suggested that VW is actually selling a performance hybrid.
Toyota set a standard for hybrid drivetrains of hitching a low-displacement engine using Atkinson cycle valve timing to an electric drive motor through a virtual continuously variable transmission. Ford’s hybrids use similar technology. However, for its first hybrid sedan, Volkswagen threw that formula out the window.
The 2013 Jetta Hybrid goes with Volkswagen’s strengths, relying on direct injection, a turbocharger, and a dual-clutch gearbox for the internal combustion part of its hybrid drivetrain. With only 1.4 liters of displacement for its four-cylinder engine, this drivetrain looks like a miniature version of those found in Volkswagen’s performance vehicles.
In January 2013, Car and Driver added:
VW isn’t prepared to stop at simply creating a very miserly Jetta. No, it aspires to produce the quickest hybrid in its class. Select the transmission’s sport mode or just mash the accelerator past the kickdown point, and the Jetta will apply everything it’s got, good for 60 mph from a stop in less than nine seconds, says VW. With a claimed curb weight of “less than 3310 pounds” this seems feasible, as we’ve clocked a 220-pound-lighter, 170-hp Jetta 2.5 with the conventional six-speed automatic at 8.4 seconds to 60 mph.
Honda’s 2004 Accord hybrid – “Sips Gas. Hauls Ass.” – claimed performance and efficiency, but only got 4 mpg more than the 4-cylinder Accord EX. It didn’t sell as well as competing hybrids and was discontinued in 2007. So I wonder whether the hybrid market is ready for another performance hybrid.
I was both wrong and right about turbocharging. My gearhead stepson told me that a lot of turbocharged cars didn’t require premium fuel. But in my reading I’ve found that many of the new, smaller turbos do.
Normally-aspirated engines using regular 87 octane fuel often have compression ratios around 10:1. Higher compression than 11:1 can lead to auto-ignition, or knocking. High-performance, normally-aspirated engines often have much higher compression ratios of 13:1, 14:1, or more, and therefore require either high octane fuel, or special timing and sensors to avoid the knocking.
With low-pressure turbocharging, engine designers dropped the compression ratio to maybe 8:1, anticipating that the turbo would boost the effective compression ratio to maybe 11:1. Some of those turbos included what my stepson called a “no squelch zone,” (piston cavity?) to prevent the buildup of heat in the mixture.
Now a normally-aspirated, regular-fueled Jetta S lists a compression ratio of 10.3:1, while the turbocharged Jetta GLI and Jetta Hybrid list unboosted ratios of 9.6:1 and 10.0:1, making them high-pressure turbochargers. Their boosted effective compression ratios are probably well over 11:1, thus requiring high-octane fuel and direct injection. Mazda’s SkyActiv-G claims a 13:1 compression ratio with regular fuel, but includes multi-hole injectors, piston cavities and 4-2-1 exhaust to quickly scavenge residual gas.
According to all reviews the Jetta hybrid is peppy and fun to drive, but I wonder who will buy a hybrid with a complicated engine that can’t deliver competitve fuel efficiency.
Update 2013-04-05: NY Times’ Behind the Wheel column just reviewed the Jettabrid and also saw it as a performance car: “The car represents a mix of efficiency, precise handling and high-speed confidence not previously offered in a hybrid.” They also found it hard to achieve the EPA 42/48 mpg rating, but they didn’t mention the turbo or the premium fuel aspects.