Hi there. I am a new G37 owner and I noticed that the gas station I usually fill up at has "non ethanol" gas. As far as I can tell it would be a preferable option, but it has a lower octane (90 without vs. 93 with ethanol). I know our engines have a somewhat high compression ratio (in the past I thought that high octane was only really needed for forced induction?), and wanted to solicit opinions on which one would be preferable. I also fill up at a local grocery store that has the option to put fuel cleaner in at an additional cost ("Additech") but it, like most gas around here has ethanol. I don't know if that would be even better but my inclination would be that the non ethanol gas would be the best solution?

Thanks!

 

The G is optimized for 91 octane fuel. Unless you've an aftermarket tune for 93 octane, pumping 93 won't help... But it won't hurt, either. However, pumping 87 will likely reduce your performance and MPG, and in a worst case situation your engine might start knocking.

AFAIK, 90 octane is something called REC-90, for "recreational" use, like powertools and little engines more rough than a typical car engine. Something about those engines not being designed for octane additives. Google REC-90.

 

Thanks for pointing out REC-90. It looks like ethanol can gum up carburetors so it's used for things with carbs. But as far as I can see, it's recommended for performance cars as it has more energy and offers better throttle response. As long as it's not detonating early I don't see any drawbacks, and it offers better fuel economy.

That's all from a cursory look at REC-90 but it makes sense. I plan on getting an OBD2 monitor soon and I guess I can just keep an eye out for any knock? I do hope to start with an intake and exhaust and hopefully get an ECU tune so it would be good to know if the 90 would have any detrimental effect. But at least initially it doesn't look like it

 

The non ethanol gas is pricey, we are already paying for premium with these cars. When non-ethanol was cheaper I used to run it fairly regularly, got 5 to 7% better gas mileage. From what I know it provides more power, more explosive combustion which helped the fuel mileage and would help power. However now you pay a 20% approx extra for non-ethanol performance which is not huge.
The higher octane is for high compression engines, it actually resists combustion to aid in optimum ignition timing for higher compression engines.
Around here, East Tennessee, premium is 93 or 92 octane, mid-grade, next, is 89. So you have no choice than to go with the 93 premium.

 

Non-ethanol is best from what I’ve seen, we have ethanol around here in everything but premium, and it sucks. Regardless I just run cheap 87 in my G35 and I send that bitch a few times a day…no knocking yet, lol.

 

Ethanol mixed gas will perform better due to it having Ethanol. As an example, G/Zs that run "E85" are running 75-85% of ethanol and are making tremendous power just on higher concentrations.
One of the drawbacks of ethanol is that it's hydroscopic (introduces moisture due to lower evaporation levels) and it evaporates faster because it's ethanol.
So a full tank of non ethanol will last you longer than one with but it will perform under due to not having ethanol.
One of the pros about non ethanol is that if chosen, you should not have any fuel contamination issues and your fuel system overall will be in better shape than one with ethanol.