Quote:
Originally Posted by Baldeagle
Curious question. Does anyone know how many degrees Subaru’s VVT phases the cam timing when it operates under the Atkinson cycle? Perhaps more relevant to this compression ratio discussion, does the ECU phase the cam timing to control knock? If yes, how much does it reduce the effective compression ratio?
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If you are curious about that information, you can download the factory ECU tune files (you should be able to find the files online) and open them up in a software called Rom Raider. All the timing data is there for the 2.0. I expect the 2.4 software to work in a similar way, just with a different values in the tables.
Yes, it retards timing to control knock. A standard car actually knocks all the time, most often when driving at low rpm with high load. The ECU will reduce timing on the fly for individual knock events. And if it knocks consistently (eg. if you have bad fuel), there is something called the Ignition Advance Multiplier which is then reduced, which retards timing everywhere.