94 AKI vs. 91 AKI Fuel
 

Anybody have anything to report as yet regarding performance with 94 octane vs. 91 Octane fuel Premium pump fuel?

Fuel with a higher octane rating doesn't have more power...

Not inherently, but it may allow the ECU to provide more timing, which could increase power output. In my experience, turbo Subaru ECUs (which require premium fuel) will react differently to 91 vs 93, and I would expect the same could be true for the BRZ.

The OP has a valid question, and I look forward to real world answers.

The octane, AKI, is the anti knock index. It dose not have more power or MPG. What id dose do is the resistance to prevent the engine from "knocking". Your car dose not need anything other than what the car is recommended to use. Unless the engine is in not healthy and knocks use higher octane.

Turbo engines have a higher compression ratio and are prone to pre mature ignition (engine knock) require higher octane gas to cope.

Dont wast your money on octane if your car donst need it.

Thanks for the replies.
I think I need to rephrase my question.
My question is not about the difference between 94/93 AKI and 91 AKI fuels. I am familiar with fuel octane quality differences.

My question is for current owners and whether their car or they as driver perceive or observe any difference. Almost all cars are equipped with knock sensors today and so can adjust to a certain range of fuel octane level by retarding the timing when knock is detected.

"...The engine is designed to operate at maximum performance using
unleaded gasoline with an octane rating of 93 AKI (98 RON) or
higher. If 93 AKI (98 RON) fuel is not readily available in your area,
unleaded gasoline with an octane rating of 91 AKI (95 RON) may be
used with no detriment to engine durability or driveability. However,
you may notice a slight decrease in maximum engine performance
and you may hear some knocking (pinking) of an engine while using
91 AKI (95 RON) fuel. Use of 91 AKI (95 RON) fuel will not affect your
warranty coverage...."


The question is whether anyone has perceived or observed anything different when using 91 AKI fuel vs. a 94/93 AKI fuel?
example: knock with 91 AKI is everyday driving?

Just curious

cheers

I don't own one yet but if the owners manual recommends me to use 93 I wouldn't think twice. Im guessing its hard to get 93 octane in some country's and was easer to build all engine's with the same compression ratio. Ill have to go looking for those numbers.

Good question. I hope someone will have noticed the difference

Some states max out at 91 AKI (meaning that the highest grade you can buy at a gas station is 91 AKI); particularly, California, home state of Toyota's US headquarters. I imagine that auto manufacturers keep this in mind; when I rented an E90 328i in LA, it said "minimum 91 octane" on the fuel filler, which makes sense, since it had a direct injected N52 engine.

The FA20 / 4U-GSE on the BRZ / FR-S is 12.5:1 compression, and direct injected, so feed it the highest grade you can get at the pump. I imagine that the ECU should be able to map 91 just fine, considering that other cars that require premium can do the same, and that they knew this car would have to be able to be fueled in states like California that don't stock 93.

I'm nearly certain that you won't get engine knock on 91 aki, I highly doubt that the manufacturers would do that. I don't think we'll know about the extent of the performance loss unless someone's dynos the same car, same day, same dyno with the two different fuels. I doubt subjective impressions will be terribly helpful in figuring anything out, unless it's a massive power loss.

I think 91 should be fine. I believe in the manual for my Evo it called for at least 97 or something like that. That was pretty impossible for me to find here in CA. I never had a problem running 91 though. I think as long as you run the premium fuel, you'll be alright.

From the BRZ Specs page on the Subaru Website:
"Fuel requirement: Premium unleaded gasoline (91 octane). Recommended: 93 octane."

The owner's manual recommends 91 (at least that's what printed in mine).

I live in Southern California, and I can't even buy 93, so the point was kinda moot.

I remember someone telling me that premium in other countries is different than premium in the US. So their 93+ is probably rated differently to our 91 premium here.

97 RON = 92-93 AKI, at least according to Wikipedia.


You're most likely thinking of RON vs. AKI octane ratings.

Thanks Subie. I couldn't remember what it was they told me, I'm pretty sure that was it though.