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Audi ACK, ALG, APR, AQD, ATX specs: 2.8L (170.9 ci) 6-cylinder, 81 x 90 mm (3.1890 x 3.5433 in) bore and stroke, 10.3:1 compression. Rated 193 hp. DOHC.
The Audi ACK, ALG, APR, AQD, ATX is undersquare — the 3.5433" stroke exceeds the 3.189" bore by 10.0% — a layout that trades peak RPM for leverage and torque low in the range. The 3.5433" stroke puts mean piston speed at 4,000 ft/min around 6,750 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 28.5 ci (467 cc).
10.3:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
Factory fitments include the Audi A4 (B5), Audi A6 (C5), Audi A8 (D2).
| Displacement | 170.9 ci / 2.8 L |
|---|---|
| Bore | 3.189" |
| Stroke | 3.5433" |
| Cylinders | 6 |
| Compression ratio | 10.3:1 |
| Bore/stroke ratio | 0.9 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 193 hp |
| Bore/stroke character | 0.900 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,543 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 28.5 ci |
| Static compression | 10.3:1 — in the range that usually runs on pump premium |
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