A Peek at Variable Compression


By Klaudia Black

How it Works . . . But Should it?


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These days, the older tech of variable timing no magic trick. The feature has actually been around for quite a while, such as Honda’s first use in the 1983 CBR400 and then in the more popular, nearly 20-years later, V-Tech performance vehicles. Back then, who could imagine a daily driven, naturally aspirated 4-cylinder car engine could produce nearly 200 horsepower! Well things are changing again because Audi now has designed a variable crankshaft -- but is this really a good idea?


In a recent press release, Audi coined their design as Variable Compression Turbocharging, or in short “VC-Turbo.” The feature will allow a motor to change compression under performance and economy situations. And at first, this tech seems very complicated, but can simply be thought of as the same concept as variable timing.


Want to know how it works? Then think of it like this. If piston reaches compression stroke it’s at Top Dead Center. At that point both valves are closed. Now freeze that moment in time and lower the piston a touch. Ro do this you would have to spin or basically “degree” the crankshaft a touch. Right?



Well that that’s basically how this system works. There’s an electronically controlled actuator assisted by a mechanical lever that degrees the crankshaft during operation which ultimately changes the compression ratio at any given moment of driving.


But why do we really need this technology when there are less expensive alternatives that eliminate the mechanical cluttering of this feature? These days, mechanics of vehicles are becoming overwhelmingly complex . . . and unnecessary.


Overall, this is a great technological feat but, but currently one that is truly unneeded. Our hats off to Audi, but At least for now this could be looked at as a marketing ploy to sell as a feature of performance and economy at the flick of a switch. If that’s the case, then stick on a turbo charger and hybrid unit.







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