Quote:
Originally Posted by fecurtis
I'm sure this topic gets beaten to death around here. The short answer to your question, use as low of an octane as you can without getting any knock (knock is where the fuel combusts before it is supposed to).
Running fuel that is too high in octane is actually bad for the engine since it can burn too slowly, contrary to popular belief, high octane gas isn't "cleaner" and it won't get you better mileage (using octane higher than what the engine was designed for actually decreases mileage), it just burns slower which some engines (such as forced induction engines) require.
So if BMW suggests a minimum of 89...I'd use 89. If my 335i requires a minimum of 89, I'd just put 89 in it. It isn't because I want to save the money (the marginal savings is nice though I suppose) but because that means 89 is the most efficient fuel to use for the motor.
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Exactly. There was a tv show up here that proved that a Woman who used 93(though it was cleaner burning and increased MPG) instead of 89 actually got worse mileage and expelled higher emissions with zero performance gain . This was all proven on a dyno on the show. I imagine using 100 might be bad for your your engine, using 93 will NOT be bad for your engine. With todays knock sensors You could run 87 and not have any problem other than slight decrease in performance. In some cases using 93 or 94 can yield minor/insignificant hp gains.