Taking one anecdotal dealer-based tech's word for it over the Hyundai engineering team? Your money to waste, I guess....
Even the statement about high-compression is off, it's not the engine compression (which typically starts LOWER on turbo and supercharged engines) it's actually the additional combustion chamber pressure from the additional atmospheres of pressure (and heat) that can cause pre-detonation, and Hyundai has done the math, so stick with the MANUFACTURER recommendation unless you reprogram it with a tune that can take advantage of the extra octane. Otherwise you're just blowing that octane and your cash straight out the exhaust.
10.5 to 1 is high for a Turbo. Especially one not running alcohol. The NA is pretty dang high. Either way. And the hp from a 2.5 with over 13:1 is suspect. I believe they are making up for the compression by killing the cam timing just to run 87. Otherwise a 13:1 2.5 would have more HP. But Either way, your right, the car will retard the timing to whatever extent it needs. Knock hasn't really been an issue since variable valve timing and computer controlled spark and fuel. The vehicle will vary the afr and timing of the engine if stressed from towing or altitude or heat soak or whatever and cut back power. 93 will allow it to adjust less.
I still haven't seen a car on the dyno that didn't make a couple more HP with 93 than 87. The car advances the timing up to the point of knock and backs off. More octane gives it more advance room. But the hp isn't a noticeable amount. Many vehicles do say run 93 for towing. Even old ohv v8 with no cam timing adjustment. The engine gets stressed towing and 93 will resist early detonation or knocking so the engine can hold more performance without having to retard timing or adjust afr
I don't know how the Hyundai works, but GM and Ford both use fuel analysis every fill up that does use a different map for 93 or e-85.
People are willing to pay 400 dollars for an intake that makes the car make a sucking sound while not making any HP (ive seen them lose HP actually). Change out a vent metered air BOV to an atmosphere release version just to go psssh when they rev up. So it's up to the buyer of they want to spend a dollar a gallon to get 2-3 HP. But more money is spent on K&N, resistors on the MAF, fans in the intake, magnets on fuel lines, spirals on throttle bodys etc etc etc and other gimmicks that used to claim more HP.
