Quote:
Originally Posted by Zhangy
I guess thats why 2011 gt500s got knock sensors
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They still knock dangerously on the stock tune with anything under 91 if you get into boost. Higher Octane is required in cars with high compression because under high compression the lower octane fuel will combust before TDC, this is "knock"(our FA20). In order for the car to adjust for itthe knock has to occur and it has to adjust and attempt to predict it after the knock occurs for the next knock. That is where the extra wear will occur, in fact it happened to people's di seals in early tunes and FA20s.
However, the GT500s have pretty low compression due to the super charger (I think its less than 9:1). They require high octane because of the supercharger. As long as the sc is not putting boost into the engine, the compression of air should be the factory 9.1:1; this does not require special fuel. But when the boost is applied, even slight throttle, you end up with 16-18psi sitting in the chamber at BDC Bottom dead center
then you compress it by 8.4:1, and you end up with a really high pressure - this requires high octane so it doesn't ignite itself too early. This is a similar issue to the FRS.
The sheer higher compression can cause the pre-ignition, engines with similar compression like skyactiv and such got away with lower octane by cooling exhaust gases quickly and such but the result is less power. The FRS however has some equal length headers and 4 injectors per cylinder etc etc to get us that 200 hp or 100hp per liter...