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Dueling Fuel Stretchers

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Posted by Jeffry L. Johnson on June 21, 2004, 7:21 pm

Dueling fuel stretchers

One VW Jetta turbo diesel faces off against a Toyota Prius hybrid to see
which technology makes more cents

Sunday, June 20, 2004
Don Sherman
Special to The Plain Dealer

In my humble opinion, fuel cells are a long way off. Perfecting
hydrogen-fueled, electrically driven automobiles and creating the
infrastructure to support them is likely to take 20 more years.

So what do we do in the meantime, now that pump prices have crested $
per gallon and some worry that they might go much higher?

Aside from bicycling or jogging to work, there are two viable means of
trimming your fuel bills already on the market: diesels and hybrids.

One VW Jetta TDI and one Toyota Prius face off here in a head-to-head
driving comparison to help decide which technology makes more sense for
saving fuel and curbing emissions.

Diesels are fundamentally more efficient than gasoline engines, on
several counts. Each gallon of diesel fuel contains 10 percent more
energy than a gallon of gasoline.

Diesels don't squander energy by pumping the air they need for
combustion past a throttle as gas engines do.

Their expansion ratios (the flip side of an engine's compression ratio),
are at least 50 percent higher, to extract the maximum amount of useful
work out of every drop of fuel.

The turbocharger fitted to the Jetta's 1.9-liter four-cylinder diesel
engine helps recycle energy ordinarily dumped out the exhaust.

The Toyota Prius hybrid approach employs a tag team of gasoline and
electric power.

The 1.5-liter gasoline engine contributes 76 horsepower and an electric
motor kicks in 67 horsepower more for acceleration and passing. At
stoplights and during low-speed operation (below 25 mph), the gas engine
plays dead to save fuel and eliminate emissions.

Nickel metal hydride batteries mounted in the trunk are automatically
charged on the roll by a second motor-generator driven by the engine and
by the main motor, which becomes a generator during coasting and braking
so you never have to plug in at night.

On the road
Compared with the noisy, smoky diesels of yore, the Jetta is a
heartening turnaround. Its clatter is muted and exhaust stream is
commendably transparent.

Nudge the accelerator and there's an eager surge forward with little
vibration. Your neighbor will never know you're driving a diesel unless
you confess.

A heavy flywheel used to smooth out engine operation and a 4,500-rpm
redline make the Jetta feel like it's sprinting in concrete shoes. At
least the turbo helps minimize sluggishness during passing.

Even though this is the last model year for the current Jetta design,
its steering cuts smartly and holds corners confidently. What it lacks
in pure speed it makes up in poise and agility.

Compared with the Jetta, the Prius feels like a TomorrowLand attraction.
Its envelope is shaped like an airplane wing to slip through the air
without a ruffle. The interior is bright and airy. Instead of a normal
instrument panel, there's a centrally positioned energy monitor and a
digital speedometer.

Starting, shifting and driving procedures are all slightly eccentric.
Since the Prius rolls on super- narrow energy-saving radials, it has
less of a grip on the road, and it is less of a driver's car.

The powertrain is silent except for the click of relays and the hum of
electric motors. The energy monitor reports that amazing things are
going on to stretch a mile or two more out of each teaspoon of gas.

Since EPA mileage figures aren't always dependable, a couple of test
drivers spent a day negotiating city traffic in Ann Arbor, Mich., and a
second shift journeyed at the speed limit across southern Michigan

A Jetta and a Prius were driven nose-to-tail, and the two drivers
swapped seats in a concerted effort to minimize speed, weather, traffic
and driving- habit variables.

Results were very consistent with EPA ratings in the case of the Jetta,
less so for the Prius.

In city driving, the Prius was the clear winner, logging an amazing 52
mpg versus the Jetta's not bad 34 mpg.

Highway mileage was practi cally a tie -43 mpg in the Jetta, 44 in the
Prius. Both of these fuel squeezers are capable of tripling an average
SUV's mileage.

Highway mileage that's lower than city mileage is a hybrid quirk.

When you're cruising at 70 mph, key efficiency boosters such as shutting
off the engine and recouping braking energy to recharge the batteries
simply don't apply.

So the Prius has to rely on its aerodynamic shape and the inherent
efficiency of its gas engine to wring maximum miles from each gallon on
the highway.

At the test track, each contender earned its fair share of the glory.

The Prius was quicker accelerating both from rest to 60 mph and from
30-70 mph during a simulated pass.

The run to 60 took the Toyota 10.7 seconds and a second longer for the

The passing gap was wider: the Prius went from 30 mph to 70 mph in 10.7
seconds (a coincidence) while the more sluggish Jetta required 13.6
seconds to accomplish the task.

Skinny tires proved to be the Prius' Achilles' heel in braking and
cornering tests. The Jetta stopped 20 feet shorter from 70 mph (172
versus 192 feet) and was able to corner better.

The tailpipe competition
One category where the hybrid Prius defiantly and victoriously flashes
its taillamps at the Jetta is exhaust emissions.

In terms of regulated pollutants, there's a world of difference between
these two technological points of view.

Thanks to a broad range of special features, the Toyota Prius is
certified as a super-low- emissions vehicle. No cleaner
hydrocarbon-fueled vehicle exists and the only emissions category beyond
SULEV is a true zero-emissions vehicle such as an electric or fuel-cell

The VW Jetta resides at the opposite extreme. The Environmental
Protection Agency category it meets allows 30 times the nitrides of
oxygen, 15 times as much unburned hydrocarbons, and four times the
carbon monoxide allowed by the SULEV standard.

That's OK for most parts of the country, but five states - California,
Maine, Massachusetts, New York, and Vermont -don't accept cars of the
Jetta's emissions caliber, starting this model year.

The hope is that the advent of low-sulfur fuel (due in 2007) and the
arrival of emissions controls already in use in Europe will save the day
for diesels and allow them to be certified in more stringent emissions

That makes the Toyota Prius today's true green machine - a car that's
just as friendly to the environment as it is to your wallet, although to
some driving enthusiasts the Jetta probably will be more appealing.

Sherman is the technical editor of Automobile Magazine and a free- lance
writer based in Michigan. He has covered the auto industry for 33 years.

2004 The Plain Dealer.

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