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It is definitely what's under the hood that separates the S4 from the normal A4. Sure, there's an improved suspension, better wheels and tires, and some interior upgrades. But most observers will still think you are driving an A4 -- that is until you step on the gas! Notice the "5v" badge on the side of the engine. |
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From this angle its hard to tell that there's a biturbo engine in there. However, the Xenon lights and body-mounted foglights are a dead giveaway (not to mention the S4 license plate). |
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This shot very clearly shows the biturbo system in the distinctive "V" arrangement. I think the badges on the engine itself are impressive looking. |
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Here's a closeup of the engine block with better detail on the badging. |
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This is a nice cross-section drawing of the biturbo system found in the S4. |
