.
I can't remember the last time I ran anything other than Premium in any of the cars. Never encountered a CAT, spark plug fouling or rough running issue. Had experimented with Reg and can feel the difference in every car besides lower mileage. Depending on the brand and octane rating there will be a reduction in mileage and performance including smoothness of the engine.
As to your question, there are no sensors which causes the computer to change engine management from that of a Polestar to Non Polestar settings. To fully answer both your questions however.
1) If you car calls for Premium and you use Reg the performance will diminish greatly. Due to Pre-ignition / knock / pinging the computer will dial back timing to keep the engine from damage. Performance is down and you will give the car more fuel to keep up with the performance you are use to. It is already requiring premium so using regular perhaps may feel like you are driving a Non Polestar but it's not because the computer has a Polestar or Non Polestar program to choose from.
2) Problematic and potentially damaging because the car is already programmed for Premium.
Excerpt From:
Engineering Explained: High vs Low Octane Petrol
With fuel prices staying fairly low recently, is it worth it to shell out extra cash for some premium petrol? And what do those numbers mean anyway?
www.carthrottle.com
"The octane rating of a fuel is a measurement used to indicate its resistance to engine knock. A fuel with a higher octane rating will have more resistance to knock. Another way of thinking about this is how much compression that fuel can handle. A higher octane fuel can be compressed (along with air) more without detonating as a result of the heat from compression."
-----------------------------------------------------------------------------------------------------------------
In the segment below from the link and then the video following there seems to be a contradiction if the Premium fuel is better. I can tell you from experimenting since the late 70's with Leaded to Unleaded and Lower to Higher Octane fuels there is a difference as indicated in the video. Performance, mileage and engine smoothness even differs between Chevron vs Costco. Chevron remains number 1 and Costco 2nd on my choice of fuels. As mentioned also the cars run smoother and cleaner as I've never had rough running issues.
3. Will road cars perform better with high octane fuel?
.
