Abt Audi AS4
Nearly two years of experience of tuning the five-valve turbocharged engine has allowed Abt to turn up the wick a bit more compared to previous versions of the 1.8t engine. The most-powerful version had around 285 bhp, but extensive testing and new components have allowed the 300-bhp barrier to be exceeded without prejudicing reliability.
All the tuned 1.8t engines up till now have retained the standard rapacity of 178lcc with a bore and stroke of 81.0 x 86.4mm. First off, Abt has gone for a near 2.0-liter capacity with a bore and stroke of 82.5 x 92.8mm. New oversized pistons with matching rods drop the compression ratio from 9.5:1 to 8.8:1 to allow a boost pressure of 1.25 bar. Using a new intake manifold, larger KKK turbocharger and intercooler, bigger valves in a gas-flowed head, larger injectors and a recalibrated ECU, the engine has been tuned to produce 310 bhp at 6200 rpm.
The longer throw crank helps make up for the loss of compression ratio and torque is 400 Nm (295 lb ft) at 4000 rpm. The exhaust system is comprised of a special high-nickel-content, cast-iron manifold mated to free-flow sports catalysts and a stainless-steel exhaust system with a 76mm diameter main pipe and twin 76mm and pipes. The gearbox is built from an amalgam of original A4 quattro and STW parts with its ratios spaced to the characteristics of the engine.
The increase in performance is dramatic--0 to 60 mph takes just 6.5 sec. and the top speed has been measured at 172.5 mph (276 km/h) on 18-in. diameter wheels and 175 mph (280 km/h) with 17-in. footwear. This is junior league supercar territory and so the suspension and brakes have been uprated with an adaptation of the STW racing suspension with height adjustment of up to 60mm lower than stock. Big 320mm vented Brembo discs and four-pot calipers up front haul the car down from speed. One of the visual highlights of the car is the gorgeous 8x18-in. O.Z. Racing magnesium alloy wheels with an ET35 offset. Available only in metallic gray finish, they counter any argument that a simple five-spoke alloy wheel is old news' The rubber is Continental's superb Sport Contact tire, sized 235/4OZR18 all round.
You can't help but notice the color of the car and the deep front spoiler, side skirts, rear valance and wing, but Abt felt that since it was selling a complete car with the AS4 in the way that say Alpine or AMG package a BMW or Mercedes, it had to carry the theme through to the interior as well. To this end, the car has been retrimmed in black hide highlighted with yellow stitching and the yellow paint continues on the dashboard and door inserts. Under the hood, the use of a bespoke carbon-fiber rocker cover and other panels give a high-tech look.
The slightly lower compression ratio is only just noticeable off boost, but in normal town driving the AS4 still behaves largely like a standard car. Once the rev counter needle has swept 'round past 3000 rpm though, things really start to happen and the forward thrust becomes seriously strong and rather addictive to acceleration junkies.
Corners are a minor inconvenience and rather a lot of fun. Brake, get your entry line and when visibility says it is safe, apply the throttle progressively. Whoosh--you're through the bend, the AS4 sticking to the road like the proverbial leech, with minimal roll and no drama. The limits of adhesion are best explored on a racetrack though, for as hard as we tried on a public roads, the car would not do anything apart from go where it was pointed.