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2015 BMW 428i - Premium vs regular

The new twin turbo 4 cylinder engines call for premium gas. How necessary is this?

Not necessarily at all if you plan on replacing the engine in the next 30 days.
However, if you want to keep your engine healthy and plan on keeping the vehicle use premium. And follow ALL of the manufacturers specified maintenance.
Hopefully the previous owner maintained it well.

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The factory says “required” which means, yes it is necessary. You drive an expensive German sport coupe. If the price of premium gas is a concern, you might want to consider selling it and buying something cheaper.

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To expand on mustangman’s comment, the 428 has a performance engine. To get that performance, it runs at high compression and needs higher octane gas to prevent premature detonation. Paying a bit extra for 91 octane gas is the price of the performance.

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  1. It’s a single turbo. It’s a twin-scroll turbo (common these days) but there’s only one turbocharger.

  2. Per page 184 of the owner’s manual;

Recommended fuel grade
BMW recommends AKI 91.
Minimum fuel grade
BMW recommends AKI 89.
Minimum fuel grade
Do not use any gasoline below the mini‐
mum fuel grade as this may impair engine per‐
formance.:arrow_backward:
If you use gasoline with this minimum AKI Rat‐
ing, the engine may produce knocking sounds
when starting at high outside temperatures.
This has no effect on the engine life.

So in this car’s case you can get by with midgrade 89 octane albeit with some knocking and some performance/economy loss. But 91 octane or better is recommended.

@ptesterman_156278 as far as BMW 4 series go, the 428i is tamest option available in the US market. The high performance variant is the M4.

I guess Pat has made a decision by now since he posted only once 11 months ago .

Probably - I didn’t notice the date when I replied. I wonder why it was at the top of the thread list when I was browsing? :thinking: