As many of you know unleaded here is 85 octane, midrange is 87 and premium is either 90 or 91.


I have been told by a fairly knowlegeable mechanic that I should not get KR with running midrange 87 (with stock pulley) at this altitude. (3700 feet)

Is there any truth to this...ATM I dont have a scantool but am wondering how correct this is.

I am around the same Altitude and i ALWAYS run 91, never anything less, ever.
Your economy will be VERY poor on anything less, as the engine will actually consume up to twice as much fuel.
And I pay around 4$/gallon for it too!

How do you know it will consume twice as much fuel? that would kill my O2 and cat within a few weeks.

my old ssei was bought in SLC and they never ran premium in it....they said they noticded no difference in economy, 28mpg on the highway with 85 or 91

Hans..how long did your old SSEi last? I think we see a point here.

Technically what the mechanic means is you won't hear any knock or pinging. Because your knock sensors will (hopefully) be working to keep your timing retarded and the engine in one piece.

While it might not be twice or kill this and that..it'* not good for your motor, when talking power or longevity and fuel mileage.

High altitude has nothing to do with it. You have an L67. 91 octane minimum with a stock pulley.

There is no question.

so why can we get away with lower octane gas in N/A cars?

because NA cars are better

Lower effective compression ratio. Though the static compression is higher in an L36, the blower on an L67 raises effective compression to a higher ratio than the NA motor. You're also dealing with much more heat in an L67 because of the blower. The intake charge is coming in at a higher temperature. Add that to the effective compression ratio, and you've got a perfect recipe for pinging and detonation.

Run 91.

Thanks, Ben. I couldn't have explained it better myself.