Utility of Chevy with soul of Porsche.., I didn't know that.

Actually ethanol mixed in your gas will reduce mpg (because of its lower btu, or energy, content), but it can increase performance since it has a higher octane rating. Again, these cars have knock sensors, so even if you put low octane fuel in the tank, it usually can compensate for it by retarding the ignition timing. You won't hear any knock (if its working properly) but you will experience lower performance.

More info from here:
E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher-compression engines, which tend to produce more power per unit of displacement than their gasoline counterparts.

I have to agree with you there, last time I was in NC I filled up on regular good ol gas and I got much more power and much much higher mpg's.
the knock sensor compensates for bad fuel just as it compensates for a poorly timed engine. yes it will absolutely run. it will run smooth too. however you will be burning either extremely rick or quite lean. drastically decreasing your power and mpg's, also either way it goes it will be running very hot as well shortening the life of your oil, sensors and all around engine!

if it's simply a daily driver, you never go above 2500 rpm's and it's not turbo charged use whatever fuel works for you. however if your turboed (already much hotter engines) and you have any mods in the car or you love to push the speed limit then only go premium. Volvo spent millions of dollars on these engines from concept to testing, always do what they recommend and you and your car will be happy. doing anything else is like driving into a dark tunnel with no lights, you simply don't know what exactly will happen.

Seriously, no dis-respect intended, but WTF are you talking about? :confused:

If you're advocating following volvo's recommendations regarding what octane fuel rating to use, I am with you on that one.

lol yeah sorry i tend to rant. but yes i am saying follow Volvo's advice, you cant go wrong.

The T5 compression ratio is lower, and ALL Volvo RN or RNC motors are interference engines. The compression ratio can be changed many ways such as; stroke, piston design, combustion chamber shape or size, head thickness (such as having the block or head shaved because it was warped from overheating, this is very common when repairing a blown head gasket), the computer in our Volvo CVVT and Dual CVVT engines has the ability to change the compression ratio constantly by changing when the valves open and close. This changes the amount of air/fuel mixture enters the cylinder. By adding air/fuel into the cylinder the compression ratio is increased because the cylinder volume remains constant. Think of it like this, a compression ratio of 10:1 is a volume of 10 units compressed into the amount of space normally occupied by 1 unit (10 liters of air pumped into a 1 liter bottle). With CVVT the valves can open earlier and close later, allowing more volume to flow through the valve. Imagine filling a bicycle tire with air, or a water bucket using the spigot, if you hold the valve open longer you increase the volume. This concept is multiplied with forced induction, turbo charged, engines because the turbo compresses the air before it enters the cylinder. This means more fuel must be injected into the cylinder to maintain the correct air to fuel ratio. More air + more fuel = more power, without increasing engine volume. So the T5 engine needs to have a lower compression ratio because as the RPM increase the turbo will force more air into the engine raising the compression ratio. So the T5 has a lower (8.5:1) compression ratio, but as the engine RPM increases so does the compression ratio. This is the same with all forced induction engines. The CVVT system can also increase the volume of air/fuel that enters the cylinders, raising the compression ratio. Not all CVVT systems WILL do this. Some work by helping to remove more exhaust gasses from the cylinders to make room for the intake of air/fuel mixture, while others create a vacuum in the cylinders so that when the intake valves open more fuel can be pulled in.
This is why the octane rating is important, even on the lower compression T5 engine. Always use the fuel type that is recommended by the manufacturer.

I was with you up until here. No, CR is static, valve timing has nothing to do with it. Now if you had said "effective CR" I might have let it slide, or cylinder filling, or VE, etc. Wrong on all these counts.. :confused:

See my earlier posts in this thread for more details on CR definition.