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The fuel thing has been covered. It really helps to know "WHY?" Here's a lay-person (like myself) take on it:

There's a misconception that expensive cars need expensive fuel. That's not true. Octane is mainly anti-knock properties. Knock is what happens when fuel detonates pre-maturely. There is a higher likelihood of this happening when either the temps in the cylinder head is very hot and/or the compression (or pressure in the cylinder head) is very high. Basically it's so freak'n hot in there the fuel ignites even without the sparkplug. The amount of damage this cause depends on severity of the combustion and the piston position when it too much knock means better chances of Real bad damage.

So, turbo cars get VERY hot and it's forced induced (more pressure), so that's why we need high octane for the engine to run ideally and safely. If low octane is used, the ecu will "slow" everything down (pull timing)to reduce temps, which will make the car drive like arse...

That's why for most cars, it makes no diff, but for turbos and high compression engines, it makes a significant diff.

As a noob, it took awhile to figure all that out. I hope I did a good job of explaining it.
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