Originally Posted by RedDinan335i
At that elevation you llikely won't see near the gains others have reported, but you should be fine on 91. As for you question on octane boost in a bottle...Don't even bother. Too many tests have proven them ineffective at actually raising octane. The only exception I'm aware of is a Torco additive. I do know some who've had good results using that on other types of boosted setups. The other method is find someone who sells unleaded race fuel and mix it with your pump gas to the desired ratio.
I started looking into this because I live in the southwest and because of regional agreements octane is capped at 91 here regardless of station. Living in Utah, I'm sure you're aware. I think your elevation is a little low, most gas stations don't start dropping the minimum octane rating to 85 until you reach the rockies at around 6-8000 feet.
I only purchase gasoline at Chevron or Shell, because of the nature of additives and detergents they use being slightly different from some other top tier gasolines. However, there has been at least two occasions when filling up I received a "bad tank of gas" where; for whatever reason, the gas was just shitty, when this happens the engine misses and chokes like it's octane starved.
I'm lucky enough to have a Rebel station just down the street that sells racing 100 (damn stuff is as blue as tidy bowl). The engine performs very well with one gallon mixed with 91. I made some inquiries with my local BMW dealership. A technician told me Lucas Octane works well with the N54. He explained this opinion was off the record because recommendations of this nature go against company policy.
So I tried the product and it performed better than the racing fuel. My drive from Vegas to Kingman was gravy. The engine performed so well that I was finding it quite difficult to stay anywhere within the 70 mile-an-hour speed limit. The local highway patrol was kind enough to remind me of this.
To address the contention that some of the studies find no real increase in octane values when added to a tank of gas is not something I would try to refute. Personally I don't care what it does to the octane values. All I know is the engine performs A LOT better with this stuff. The other benefit is one bottle treats about two full tanks at 8-10 dollars a bottle which makes it a little more economical that a gallon of racing fuel at $5.99. Lastly, it says on the side of the bottle that it's approved for turbos.
If you're concerned about performance at 91 octane I recommend trying this brand to see if you have the same luck I did with your application.