Thoughts on using 89 octane
 

So I mostly commute with my BRZ and lately rarely goose it over 3-4K. I have other cars to play with. So last time I got gas they did not have 93 and I out 89 in and the car felt exactly the same. No I did not log it to see if there was knock or anything funky going on. But if I did not know it was 89 I would never be able to tell for commuting. Thinking it would be great to do this and save some money burning gas on my long highway commute. Any thoughts? Is there and OFT OTS tune for 89?

take a ots tune for 91oct and open timing B map and reduce the timing, like -1/-2 degrees from 2k to redline
should be ok

will consume a little bit more fuel than usual, nothing extraordinary thought

Any Costco gas stations in your area? The price of Costco 91 for me is basically the same as 89 at other pumps (or even less).

Friends don't let friends RB

oh, wait

Really? You can't pump your own gas in OR and I have had them put 87 in my car. It feels so lazy every time. I can instantly tell.

What’s the $ spread on 89 to 93 or even 91 in your area? It’s maybe $.30 here or < $7 for a fill up. For $7 I’d just find a station with at least 91oct. These cars are knock sensitive enough without running the wrong gas long term.

The stock ECU uses a base ignition table in combination with a ignition advance table. The base ignition table is the minimum ignition advance that the engine will run. The ECU then adds a percentage of the advance table on top of the base table. This percentage depends on how much knock the engine is detecting. I believe every time you start the car the ECU is running 70% of the advance table on top of the base table and then increases that to 100% as long as there is no knock detected. On the flip side, if there is knock detected it would use less of the advance table down to a minimum of 0%, in which case it would just be running the base table.

For example: the base table says to run 10 degrees of ignition advance and the advance table is an additional 5 degrees. So the engine will be running anywhere from 10 to 15 degrees of advance depending on how much knock it sees.

When using lower octane fuel my guess is that you will be seeing more knock and therefore be running less ignition advance which ultimately means less torque. It's possible that the octane could be low enough that you are running only the base table (0% of advance table) and the engine is still knocking because it has no more room to retard the timing further. This is probably unlikely but would have to be verified with data logging.

How will this affect your engine long term? I couldn't tell you, but maybe this was still helpful...

Guess I will stick with 93, currently running a Wayne rom tune for 93. Data logged last summer without any knock. Maybe I will try 91 and datalog. My thought was that since the rpm’s rarely get above 4k in a highway commute that the ECU could easily compensate for lower octane. I need this car to last as my commuter, so better to be safe or prove it works.

This should throw a code and trigger a MIL (check engine light), no?

You could be right. From my understanding the ECU is only looking at knock and will adjust as needed to prevent it. It could also be adjusting the fuel trims, but I'm not sure on that (running richer AFR will help prevent knock). With ECUTEK the 0%-100% factor I talked about earlier is called the "ignition advance multiplier". It would be interesting to log on lower octane. If that multiplier is consistently staying at 100% then I would think the lower octane isn't making any difference.

My guess is that there's enough margin in the base ignition table to deal with the lowest octane fuel out there and this would probably never happen. Would be interesting to see some back to back testing comparing octane readings to see how much timing is getting pulled.

Really. Mine has only had Chevron Good Ole Premium 94 octane, its entire life. Well there was 89 octane crap in it when I bought it new, but that is the only alcohol my baby has ever seen.


Its for sale on Vancouver Island. It has 17,200 Km on it and is cherry, and red too. I'm trading it for a Solterra in a few weeks, so be quick. ;)

Weird. It's .65-.70 between 87 and 93 here in MD.

Here in Touristland the difference is about .40-.50 cents between 89 and 93. But gas is .40-.50 cents less at discount stores like Costco, Sam's or BJ's. I only use BJ's 93 octane because it's usually cheaper than regular anywhere else.

Or more. I've seen it as high as $0.90/gal difference.

RPM is not what causes it, has more to do with cylinder pressure, ignition timing, and AFR. I had the toughest time getting knock to go away at 2800-3krpm on my car. You will cause knock to happen easier by lugging the engine then revving it out.

This is why I only use 94 octane gas. Most of modern tuning is getting the computer to not pull time.

Sticking with 93. Car has been paid off for two years, no sense buying another with better gas mileage and a payment. I’ll just keep burning cash with all the miles she has on her.

Mine will be gone this weekend. I'll trade her for a Solterra. My excuse is I'm very old and just gave my Suzuki Samurai to my daughter. So I need a beast to haul my crap to the dump, get water for my fifth wheel and generally be useful. That it should take my fuel bill from $200 a month to about $25 is entirely incidental. ;)

At a 20k difference in price though, that $175 difference in fuel will take 115 months to break even, no?

Nothing I will think about. I am 76 and getting tired of having my ass 6" off the ground, and although my left knee is still strong, I am looking forward to an SUV. As I said I need one.



As well driving my cherry red BRZ and trying to economize the very high gas prices in Canada, is just wrong. The car should go to someone who will use it.



I have driven a Solterra, and its one the nicest thing I have driven. Its a bit strange but its very stiff indeed, about 20% stiffer than anything they have made before. As well the centre of gravity, almost 4" below the rest of its bigger cars, makes for a really great experience. Its like driving a tank, that handles like a sports car. ;) As well, if you do it just right, its 0 - 60 is about 6 seconds, a bit quicker than your BRZ. ;)

I have a bike for speed and the 86 for commuting and lowes trips. Pretty sure the bike gets to 60 in half that time :D I'm not 76 though so I get the need for something up a bit higher.

OK. I am an old man, I have had a lot of vehicles in my time. My 69 Cutlass, I built with a 502, would get to 60 ridiculously fast. My 57 Sportster was not that fast, but my KTM 300 would drop almost 60 horse into about 250lbs and was also ridiculously quick. The Solterra is an SUV and is quick because the all electric power, that it is quicker than a gen 1 BRZ, is just how it works.



I am detailing my BRZ today, for inspection tomorrow, but it does make me sad that I have to let one of my all time favourite cars go, to make the deal. I wish I were richer and could keep both of them.


The Solterra is an amazing car in its own right, and I am really looking forward to daily driving it.

My first car was a 69 cutlass red with black top back in 1988. Loved that car until it rusted out here in NY. Literally was a Flintstone car.

Reported.

Scroll up, you'll see.

No idea. I'll just log out.

I missed the fun. :(

Someone hacked PenGun's account and was posing crap about his "Solterra"