Octane: What to run in your BRZ

75277 Views 34 Replies 20 Participants Last post by Snoopysvet, 1 mo ago

donwrblue13

Discussion Starter · Jul 6, 2012 (Edited)

If you've read the owner's manual by now, you'd know your BRZ requires a minimum of 91 octane to run safely without damage, and that Subaru recommends 93. Anything below 91 will most likely result in lots of detonation, and even motor death. I want to stress here that running 87 or 89 is NOT safe and if you do that and blow your engine up under load, you only have yourself to blame.

What is detonation? We'll, it's basically when the air/fuel mix explodes in the combustion chamber when the spark plug fires creating pressure spikes usually due to low octane fuel or bad tuning. This causes damage to piston rings, among other things. It usually sounds like a loud tapping or knocking noise. Knock happens most easily when a lean Air:Fuel ratio exists, and when ambient temps are high. If you've ever heard this sound, you know how terrible it is to hear particularly if your car is on the dyno running at full load. I've seen engines nearly explode on dyno days mostly due to bad tuning or just stupidity of not having enough fuel capacity for their setups.

"It's just a four banger! Why would you need to run premium? It's not like it has a turbo!" This engine has a very high compression ratio of 12.5:1. This is high in the realm of street cars, which is why you need fuel with better knock resistance.

"So why do they recommend 93 vs 91?" They have to design the car to run on 91, because some areas of the country only offer 91 at the pumps. However, they can design the ECU to recognize 93 or 91. This car uses a dynamic advance to compensate for the lower octane (thanks visconti!). No one should have any problems running 91. Get 93 or higher of course if you can get it in your area, you'll get slightly better performance.

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stugray

· #21 · Aug 31, 2013

So I drive my BRZ at about 5000 feet altitude or higher.
It is nearly impossible to find 93 Octane gas in CO.

I read that at higher altitudes, the higer octanes are not required to eliminate knock because of the reduced air charge.
So I have to run 91 all the time.

Does anyone else have any experience at high altitude with these cars?

Stu

thewrx

· #22 · Sep 1, 2013 (Edited)

Anyone use 87 during the winter months?

Few other observations, if perhaps you filled up with a lower octane or had bad gas you ecm would just default to the "low-octane" map that basically just adjust timing.

Also 14.7 is too lean run unless its idle or very low load, at wot you are probably at high 11's maybe 12 with the ability of direct injection but nothing close to 14.

eromsdal

· #23 · Jul 28, 2014

Im running an E85 tune by Delicious Tuning... and its AWESOME!! So much power so little work done... all you have to do is tune it and have access to E85 and you got more power! Flex fuel allows you to mix the octanes, i don't have a flex fuel kit yet but will add soon for safety reasons... without the flex fuel kit you have to run out all the regular gasoline before adding the ethanol an tune! Delicious Tuning in CA, Bill Knose will hook it up!

elenamylove

· #24 · May 19, 2015

Anyone know if using Octane booster during fill-ups with 91 octane gas be good / bad idea? I can only find 91 octane in Jacksonville Florida and in the manual they stress 93 octane.

Brand recommendations would be great.

Subieman

· #25 · May 20, 2015

Near sea level octane booster should result in a noticable improvement in peak torque around 5,000 rpm. It is a very expensive way to boost octane but the engine is designed for 93 PON.

Most high octane gas around the world is 94. "Regular" gas in Europe is 91.

Where I live at 3,000 ft elevation it makes no difference because the air is too thin anyway.

elenamylove

· #26 · May 20, 2015

Thanks again Subieman - I just noticed I do have access to 93 octane gas here so I'm golden, now to find the one my car prefers the most, I'm starting off with Shell and then maybe BP or Exxon next.

Subieman

· #27 · May 21, 2015

elenamylove said:
Thanks again Subieman - I just noticed I do have access to 93 octane gas here so I'm golden, now to find the one my car prefers the most, I'm starting off with Shell and then maybe BP or Exxon next.

Where I am Shell V Power 91 has no ethanol which is a good thing. I assume their 93 just has more of the same non ethanol octane booster but I am in Canada where ethanol content of gasoline isn't as tightly regulated as in the U.S.

The only 94 I can get is from Petro Canada or ESSO (EXXON 's retail trading name up here). At my elevation it makes no difference because the engine cannot run at peak pressures anyway due to the thin air.

Reactions: 1

elenamylove

· #28 · Jun 4, 2015

I found 89 ethanol free gas, should I use that with an octane booster or just stick with a 93 octane gas with 10% ethanol? Wow, this gas dilemma is getting to me.

Subieman

· #29 · Jun 9, 2015

elenamylove said:
I found 89 ethanol free gas, should I use that with an octane booster or just stick with a 93 octane gas with 10% ethanol? Wow, this gas dilemma is getting to me.

89 isn't enough. There actually isn't any 89 the pump is just set up to draw from both storage tanks at a 50/50 ratio of 87 and 91. So if you fill with 89 you are getting gas from both underground tanks.

elenamylove

· #30 · Jun 9, 2015

You are right, its the 87 that's ethanol free. I'm just going to keep using the Shell 93 V-Power or Speedway Premium.

john hayman

· #31 · Jul 2, 2015

I buy ethanol-free when I find it, and notice better gas mileage. I normally get 40 to 42 mpg. With ethanol-free I get up to 44 mpg. What kind of mileage does everyone else get?

STIlsh

· #32 · Nov 9, 2017

How is it possible to get over 40 mpg with these engines? are you coasting down hills and putting up sails when you have a tail wind John?

bunster

· #33 · May 16, 2019

E85

eromsdal said:
Im running an E85 tune by Delicious Tuning... and its AWESOME!! So much power so little work done... all you have to do is tune it and have access to E85 and you got more power! Flex fuel allows you to mix the octanes, i don't have a flex fuel kit yet but will add soon for safety reasons... without the flex fuel kit you have to run out all the regular gasoline before adding the ethanol an tune! Delicious Tuning in CA, Bill Knose will hook it up!

Hi,
What mods are required to run E85 and cost?

huskylover

· #34 · Jul 16, 2021

which gas station has best high ocatne , cleanest burning 91 plus gas for the BRZ engine?

Snoopysvet

· #35 · 1 mo ago

I live in Cali and 93 octane is almot impossible. 91 octane will work fine

21 - 35 of 35 Posts