Hi Guys ,
right now in Montreal we are seeing Gas prices at 1.28$ - 1.36$ Per liter... seeing that the Stelvio takes premium gas.. can we get away with regular octane ? or possibly 89 ?
in most cars the result is the computer retards ignition timing to prevent knock, and you reduce HP and fuel efficiency as a result. Some cars (Audi in particular) are unable to compensate for the lower octane fuel enough and suffer significant knock problems, which will prematurely wear out engine components (primarily the pistons, connecting rods, bearings, and cam shaft), or in some cases cause catastrophic engine failure.
There's a good youtube channel called EngineeringExplained, he recently covered some information pertaining to this. summary is that for normal driving most cars that don't suffer from knock problems are "better" with 87 octane because the % of power increase is less than the % additional fuel cost, but only as long as the engine can compensate for the low octane fuel. However some tested vehicles saw as much as a 5-10% increase in horsepower & torque from the better fuel under load.
I suspect (but haven't tested) the high compression + 22PSI of max boost in our cars will result in significant knock problems. I did the calculations based upon the published displacement, bore and stroke numbers and got a 17.38:1 compression ratio, which is bordering on insanity if that's correct, and tells me that running anything lower than 91 octane will probably result in bad knock.
FWIW, the official requirement is Premium unleaded, 91 octane (R+M)/2
