A5 TDI Nearly Outmuscles S5

March 13, 2008
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You probably wouldn’t expect a car that bears the declaration, “the cleanest diesel in the world,” to be much fun to drive. But the A5 3.0 TDI — one of two such examples we drove recently — is remarkably responsive. The car that stands up to this claim — the very same one that ran recently in the Challenge Bibendum in Shanghai — is equipped with a six-speed automatic transmission plus, to make it better than 50-state legal, a urea-injection system that sprays a solution called AdBlue into hot exhaust gases to reduce NOx emissions.

The AdBlue solution is stored in a five-gallon tank and lasts at least 10,000 miles, such that you’ll never have to worry about it between oil changes. And if the driver ignores all of the warnings to refill the reservoir, the engine computer will very gradually and safely limit the engine’s power, according to Günther Schiele, head of TDI engine development for the automaker.

The U.S. A5’s top engine, the 265-hp, 3.2-liter V-6, brings the coupe to 60 mph in 6.1 seconds. But in Europe the same clean-diesel A5 3.0 TDI (minus the urea system) makes for a faster version that slots between the gasoline 3.2 and the V-8-powered S5.

In the A5 it knocks two tenths off that dash to sixty, allows it to hit a 155-mph top speed, and feels considerably more powerful in real-world driving, compared to the V-6.

I recently drove the A5 3.0 TDI and an S5 within a few days of each other, and the comparisons were intriguing at the least — especially when the TDI was equipped with its standard six-speed manual.

The S5 feels a little more playful, thanks to its rev-happy, direct-injection 4.2-liter V-8, making 354 hp and 325 lb-ft of torque, enhanced brakes, and a sport suspension, and it’s definitely the winner over the finish line in a straight up, through-the-gears acceleration run (4.9 seconds to 60), but the monstrous peak torque (406 lb-ft) of the TDI engine is reached at only 1750 rpm and much of it is accessible from just above idle — which could have the S5 driver lugging in fifth or sixth losing momentum and rushing for a downshift in a lane-to-lane match-up.

The S5’s V-8 is a little flat off the line; it doesn’t hit its sweet spot until you pass 2500 rpm or so, but it’s one of the smoothest we’ve tested, and the unforgettable burbling, rumbling character of its exhaust note — combined with the silhouette the A5 takes on when fitted to larger, more flamboyant wheels — brings a character to the A5 that’s very American muscle in some ways...so much that our Editor Marty Padgett declared it “ein bitchin’ Camaro.” I concur. Our test car came in a very nice, subtle Meteor Gray Pearl that thankfully did’t play matador to the troopers, but the Magma Red interior, with red-leather seats and trim, served to enhance the bad-boy feel from the cockpit.

We expected great gas mileage from this diesel coupe. But what we saw from the trip computer was better than any optimistic guess; we averaged 6.7 liters per 100 kilometers — about 35 miles per gallon — in nearly 100 miles of touring on two-lane country roads and through small towns, with plenty of stopping, varied speeds, a full-throttle pass or two, and some enthusiastic driving along the way.

That’s more than double the gas mileage (about 16 mpg overall) I saw this past week in a drive of the S5, which requires premium unleaded that, in my area, costs virtually the same at the pump as diesel.

The combination of 3.0 TDI and six-speed manual transmission was especially appealing, and I couldn’t help but wish for this diesel powertrain, matched with all the other performance extras that the S5 brings. Better yet, the S4 Avant, with the buff TDI and six-speed?

That won’t happen, according to Audi officials, who confirmed that when the A4 is eventually rolled out with this engine sometime next year, it’s likely to come in a single model with the automatic transmission. Despite the overwhelmingly positive reception to the R8 TDI V12 Concept rolled out at Detroit, the demand isn’t there yet for diesel+sport (S trim, manual gearbox), they say.

Perhaps they’re right to think that Americans aren’t quite ready for a diesel luxury coupe, but for an S-trim TDI sedan and wagon, I beg to differ.

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