Far from being just the A35’s 2-litre turbocharged engine with an ECU tickle, the A45’s power unit is effectively all-new. The whole thing is rotated by 180 degrees compared to that of the A35 (so it’s still transversely mounted) with the exhaust ports and turbocharger now on the firewall side and the intake at the front, to the benefit of airflow and cooling.
The turbocharger is different too, with roller bearings for reduced friction, and divided ducts to separate exhaust pulses for faster, less disturbed flow. Lessons learned from AMG’s hot-V V8s mean the turbocharger is cooled by oil, water and air, the latter by special ducts in the engine cover, while the wastegate is electronically controlled.
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In the engine itself there are different valves, two-stage fuel injection, separate water pumps for the block and cylinder head, a two-stage intercooler, and a baffled sump to prevent oil surge under high cornering loads. Oh, and the whole thing is put together like a proper AMG engine – handbuilt by one individual in Affalterbach.
So what does all this get you? The answer is 415bhp at 6750rpm and 369lb ft of torque from 5000 to 5250rpm. Don’t let the narrow torque band fool you either – this engine is mighty throughout its rev range, no less than you’d expect for the most powerful 2-litre engine in production, and the most powerful in any hot hatch. While we’ve seen engines at this level before, most notably in Mitsubishi Lancer Evolutions, bear in mind too that this won’t require anything like the sub-3000-mile oil changes required of that car…
Power is sent to all four wheels, first through an eight-speed dual-clutch transmission (rather than the A35’s seven-speed DCT), then through, at the rear axle, a pair of multi-disc clutches to direct power to whichever wheel needs it most. All this tech comes at a cost though, and it’s not just the purchase price – the A45 S weighs in at 1560kg, or around 80kg more than the AMG A35