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Discussion Starter #1
One can easily understand how extremely high engine temperatures, summer heat, heavy loads, and high rpms ... might recommend the use of premium gas.

I found out that the Part of the PZEV system actually creates engine knock on extremely cold starts! The system is manipulating valve timing, injector timing and injected duration.

“ brief and subtle knock of the valves during cold starts, especially in low temperatures.”

I’m going to suggest that to protect yourself from these pollution controls one might consider premium fuel use in the winter.

Just a thought and maybe it makes sense and maybe it doesn’t.
Cheers
 

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Discussion Starter #3
It isn’t the engine by virtue of vvt can vary the valve timing so compression is only 10.5 to 1 and then somehow allow for 12.5 to 1 in the expansion stroke.
Efficient even on regular old crap gas. Even though the car runs nicer on premium.
PS: I still run Premium.
 

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Variable Valve Timing (VVT) changes the compression ratio by allowing ignition valve to close latter during compression, letting compression going from 12.5:1 to 10.5:1 as engine needs. All monitored by knock, fuel and air sensors
 

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My '13 sounded worse than a diesel on cold start up. Not so subtle. Dealer said "They all sound like that" though he wouldn't let me try one to see. Figured I'd drive it 'till it threw a rod. 100K+ miles & still holding together. Never saw the need to buy premium.
 
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