Using Gas Octane below the requirement.
 

Here where I live in New Mexico, it is hard to find the required 91 octane for my BRZ. So, I've been fueling my car with 90 octane since purchase day. The car now has 8,000 miles on the odometer. The other day, I stumbled on a gas station that has a 91 octane. Filled my car up and right away, I noticed the engine is happier and more lively and responsive without the sluggishness.

Could there have been any serious damage done to the car for all those miles I have driven using only 90 octane
gas? I'm kinda worry because this is my first car and I really baby her. :cry:

Not really. 1 off on the octane reading may have the ECU dial back a bit from optimum.
Slightly.

What is the altitude where you do most of your driving?

The twins need high octane at sea level to prevent knock due to the OEM high compression ratio.

Higher altitudes will draw less air per cycle, and lower the compression ratio thereby.
There shouldn't be a problem in this case.
More is always better though, right?

Why is regular gas lower-octane in higher-elevation U.S. states?

BCJ is spot on. In NM, you're most likely at least at SOME altitude and will be fine on 90. Honestly, any "gain" from 91 is probably just placebo effect.

Thanks. I do most of my driving in the areas in and around Portales, which has an elevation of 4000 feet. Surrounding places that I frequent like Clovis, Ruidoso, Albuquerque are even higher in elevation.

It is not a placebo effect. My car feels more torquey and responsive running the 91 octane here.
There has been no noticeable issues with my car running 90 octane so hopefully no ill effect from using it. Just a little worry it might shorten the longevity of the engine and/or other components inside the car.

Cannot speak for our BRZ engines, but I took an Acura TL to 197k on 87 octane when it called for 91 octane. No ill effects, got great mileage and power, sold car and is likely still running. I use the high-test on my BRZ, but sometimes I wonder.

Yeah, 90 octane at higher elevations seem to be okay so far but I’d rather put 91 or above. I’m stuck with 90 where I live though. It’s like winning the lottery when I find a gas station carrying 91 here :lol:

just look for the stations with the most additives, and remember you can always buy octane booster if you want to see what higher octane feels like.http://www.toptiergas.com/

Unless you get the crap gas you probably won't notice too much of a difference.

Damn. And CA complains about only getting 91.

The car will make up for deficiencies to some degree. 90 vs 91 isn't a huge difference. A hot day or high altitude with 91 may be worse than a day driving on 90. I wouldn't run at altitude on a hot day with 87 or anything, but I doubt you would even see engine damage running 87 with normal driving at sea level on an average temp day. Maybe at the track, but not cruising around town.

With that said, this car is knock sensitive, so you may feel big power differences, but this shouldn't indicate that you are damaging things.

Cool video: Supercharger at altitude...I believe it was tuned at sea level (if that matters). At altitude the power was seriously under-performing on the SC probably due to knock resistance.

[ame="https://www.youtube.com/watch?v=2bhnMYvn5S4"]Supercharged vs Tuned - Long Term FRS (GT86) #5 - Everyday Driver - YouTube[/ame]

lower octanes work better the higher the altitude is.

Not really.

Station by my house offers 87, 89, 93. Almost .50 gallon more for 93

Entirely possible your local 90 stuff is junk. Where are you filling up? Mom and pop places that may not see a lot of throughput in their tanks, or places like Shell/Mobil that are top tier, and are likely to have their tanks emptied and refilled every day or two?

Also, most octane boosters are largely marketing that raise the octane rating very little, so be sure to do your research before you give one a shot.

If you're rural, some airports or farm areas have E85, (usually more like E60 at the pump,) so if that's an option you could consider going flex fuel, and get a nice tune and a power bump.

Lower octanes worked better with carbureted engines back in the days before fuel injection could correct for air density. It would be incorrect to say they work better today. It would be more accurate to say that at a given RPM in a given gear, at altitude versus sea level, there is less air density, so there is less need for as high as octane.

Now, consider the need to do a given workload. If a car was going to go up a 15% grade at 65mph at altitude versus sea level, what would need to happen? Since there is less air density the vehicle would need to increase its efforts, possibly reving much higher. In the case of a turbocharged engine, the same psi could be realised but the turbo would have to work much harder to pull the air into the motor. This is like trying to run on sand versus pavement. In my eyes, more work means more heat, and more heat for the same workload or work output means there is a greater likelihood of knock.

I could be wrong, but that is how I see it.