The manual says to use premium, use it.

performance/fuel economy

this is a great debate..you run the risk of engine knocking/pinging due to the gas mixture igniting before it should due to the lack of octane content. from what i hear there shouldn't be any significant engine damage due to the knock sensors to prevent the engine from self destructing.

the downside of using non-premium fuel is less performance and decrease in fuel efficiency as the engine tries to cope with the lower octane rating fuel. do you care about the slight performance loss?

so how much more gas will you guzzle with non-premium fuel? well chances are your gas mileage will probably not be bad enough to offset the cost of premium fuel price difference.

having said that i still put in premium fuel over the regular non-leaded and it's about 10cents/litre extra in Canada.

my 2 Canadian cents worth, your 0.00005 USD equivalent.

That saying is a bit misleading. It's not high performance engines that need high octane fuel, it's high compression engines. Most all high performance engines are high compression, but not vice versa. Hence a dinky 1.8L turbo putting out 170HP is high compression, without the performance.

With a compression ratio of 10.2 on the 330, (10.5 on the 325) it's pretty high and should be fed gas with a high octane rating. However, the engine is self adjusting so little to no damage should be result from using low octane gas; though constantly reving your engine may prove otherwise.

What fuz said is pretty much spot on. You should use Premium whenever possible and for whatever reason you want to use something lower don't go lower than mid-grade, or 89 octane. My father tried different octane on his E39 before and the saving from lower octane does not cover the decreased gas mileage.

Thanks for the responses everyone. Premium it is!

:thumbup: