The wagon is the ultimate sleeper, unlikely to arouse the suspicions of boy racers or federal officers alike--but those who know realize there are some fearsome wagons out there. Audi is the chief exponent of the ludicrously powerful load lugger. And the RS4 Avant was arguably the best of the bunch, and the fastest production wagon on Earth. It would kill sports cars on standing starts and find the grip in an oil slick. Was it the ultimate multi-purpose driving machine? Perhaps, but it acquired a reputation for poor wheel balancing and brake issues, didn't sell well and production came to an end in 2002. Now, with its rivals regularly knocking out cars with horsepower figures to worry ocean-going liners, and the RS6 bowing out, there really was no choice. The new RS4 is coming, but this didn't help those that couldn't get one for love nor money a few years back. It was a gigantic hole that just had to be filled. Then German tuner Abt Sportsline stepped in with the blinding AS400. It's even better than the car Audi couldn't make work, and Abt could make them out of any common-or-garden A4.

This car is not a cheap solution, costing 94,900 euro in complete form, which pits it against some of the world's most desirable cars with more cache. But it is a real weapon. Abt advertises the AS400 as a wagon you can take on the track, and this company from Kempten, deep in Germany's southern tuning community, isn't known for idle and flamboyant boasts. With support from Audi, this is the firm that went out and beat much better equipped works teams from Mercedes and Opel in the DTM recently. Boss Christian Abt still drives one of the DTM Audis alongside development duties for the company founded by his late father, who decided his future did not lie with the family blacksmith business. So they know a thing or two about performance tuning and track work.

For the engine, Abt could have gone about engorging the 2.7-liter twin-turbo in various formats. Abt has such a close relationship with Ingolstadt that when the RS4 bit the dust, a supply of engines made its way to Kempten. With 380 bhp coming from the stock engine, a mild ECU adjustment and stainless-steel exhaust system was all it took to get the extra 20 ponies. Abt has a 450 bhp upgrade, too, for a small premium, and the chassis could take that all day. Performance, then, is suitably rapid. Dump the clutch and leave the electronics to sort out the grip and it will hit 60 mph in 4.7 seconds despite weighing more than 3,500 pounds. Load it up with people and furniture and the times won't change much. For such a wonderfully refined car, though, the gearbox is a let down. Abt's installation of a short shifter has done nothing to help a first-second change that was already clunky and awkward. Muscle it and it will go in, but this box is out of keeping with the rest of the car's velvet efficiency.

A fully adjustable sport suspension kit drops the car as close to the road as you care to go, reducing the lateral forces and body roll in corners. Combined with Audi's sophisticated all-wheel-drive system, this all helps the beast shed the pounds in the twisty bits. You can still feel the weight, though, and it's not the kind of car to turn off the traction control and slide sideways around a mountain pass.

In truth, the RS4 was too much car for its brakes and warped discs were a common complaint. Abt came up with its own solution, an upgrade to 14.6-inch rotors at the front and 13.5 in the rear. While I can't vouch for the long-term durability, their performance is scary good. Not only does it stop on its nose, you can turn right through a corner with the ABS juddering.

It's always better to be on the power through the apex in a four-wheel-drive, but it's good to know that the car can make an emergency stop while diving out the way of something solid without meaningful driver input. And at speed, close to its top end of 181 mph in the left lane of the autobahn in our case, it feels every bit as solid as its appearance suggests. This is a chunky car that won't be affected by cross winds or even transmit minor bumps from the 19-inch wheels. The downside is that this wagon is not the most involving drive in the world,, but most people graduating to this kind of transport have grown out of such cheap thrills.

It's more subtle, too, and could go about its business in the quiet respect of the surrounding populace. Indeed, Abt's aero tweaks are barely noticeable if you aren't looking for them. A new front grille, spoiler, side skirts, rear apron and rear wing barely stand out. The four polished exhaust pipes will mark it out only with experts, as will the invariably deep rumble burbling away under the hood.

The interior is a little louder, with sport seats complemented by beautifully finished pedals and other cockpit baubles. But again it is the quality of the finish, more than the in-your-face visual impact, that shines through in Abt's products.

The new RS4, which will have around 420 bhp at its disposal and a second crack at that recalcitrant gearbox, effectively sounds the death knell for the AS400. But don't despair, as with the new, more powerful starting point to play with, Abt should be able to come up with a truly spectacular car. Will it be the world's ultimate multi-purpose driving machine? Who knows, but it should certainly be among the quickest. Boy racers beware.

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