All-New 2022 Subaru BRZ Makes Global Debut

[Tcoat]

Originally Posted by Yoshoobaroo

I bet it's still fine running on 87AKI. It may be optimized for 91/93 but I kinda doubt that being that the US public has such an aversion to using higher octane fuel for some reason. We'll see I guess. I'm excited about the C/R bump, I always run 93 in my cars anyway since they all have at least a 93 Octane tune on them anyway.

The current engines, at the lower compression ratio, recommend 93 and require 91 so there is no way that they are going to increase the compression ratio and reduce the octane requirement.

[Cephas]

I doubt they'd lower the recommended octane, but that doesn't mean the car won't run sorta okay on lower grade fuel. The ECU is smart enough to pull enough timing to make it work.

[Tcoat]

Originally Posted by Cephas

I doubt they'd lower the recommended octane, but that doesn't mean the car won't run sorta okay on lower grade fuel. The ECU is smart enough to pull enough timing to make it work.

The current engine runs sorta OK on 87. The new one is a substantial increase and would probably be pushing even the ECU to it's limits as far as correction goes. In other words it would probably run like crap. Even Joe and Jill Generalpublic would notice the difference.

[ZDan]

They likely have the same basic requirements regarding how well it runs on 87 for the new model as for the current one. Could be improvements to combustion chamber design, fueling, and spark control make it possible to have the same "driveability" with lower octane fuel with the increased compression ratio.

long/short: I wouldn't worry about it... Especially since we're all gonna use 91 octane minimum anyway!

[Transport3r]

Another point to consider is that just because the static CR is now higher doesn’t necessarily mean that the minimum dynamic CR that can be achieved by valve timing is any higher than before. If they’re going to sell the cars in NA, they have to be able to at least run reasonably well on 87, I’m sure that requirement is the same as before. Between valve timing, ignition timing, and advances in DI tech over the past 10 years, I don’t think it’s unlikely at all.

[Tcoat]

Originally Posted by ZDan

They likely have the same basic requirements regarding how well it runs on 87 for the new model as for the current one. Could be improvements to combustion chamber design, fueling, and spark control make it possible to have the same "driveability" with lower octane fuel with the increased compression ratio.

long/short: I wouldn't worry about it... Especially since we're all gonna use 91 octane minimum anyway!

Originally Posted by Transport3r

Another point to consider is that just because the static CR is now higher doesn’t necessarily mean that the minimum dynamic CR that can be achieved by valve timing is any higher than before. If they’re going to sell the cars in NA, they have to be able to at least run reasonably well on 87, I’m sure that requirement is the same as before. Between valve timing, ignition timing, and advances in DI tech over the past 10 years, I don’t think it’s unlikely at all.

They were concerned enough with the old ones to say NOT to use 87 so even if it "stays the same" they are not suddenly going to say it is OK.

[ZDan]

Originally Posted by Tcoat

They were concerned enough with the old ones to say NOT to use 87 so even if it "stays the same" they are not suddenly going to say it is OK.

Yeah, of course they'll say not to use 87 and will specify 91 minimum. I'm just saying they likely haven't changed their requirements for how the engine deals with lower-octane fuel should it find it's way into the engine. I would guess that the new engine's susceptibility to damage or poor-running from lower-octane fuel is the same as the current lower-CR engine. I.e., nothing to worry about for most of us.

[Sasquachulator]

Originally Posted by Transport3r

Another point to consider is that just because the static CR is now higher doesn’t necessarily mean that the minimum dynamic CR that can be achieved by valve timing is any higher than before. If they’re going to sell the cars in NA, they have to be able to at least run reasonably well on 87, I’m sure that requirement is the same as before. Between valve timing, ignition timing, and advances in DI tech over the past 10 years, I don’t think it’s unlikely at all.

IF the gas cap says recommended 91+ or whatever you might be able to get away with using 87.
If it says required 91+ dont even dare put less than 91.

[Transport3r]

Originally Posted by Sasquachulator

IF the gas cap says recommended 91+ or whatever you might be able to get away with using 87.
If it says required 91+ dont even dare put less than 91.

Agreed, but as @ZDan pointed out, someone will. Subaru likely has a requirement that there engine can run on 87 (once ) without sustaining long term damage. We’ll probably never know for sure though.

[Dzmitry]

Originally Posted by Transport3r

Agreed, but as @ZDan pointed out, someone will. Subaru likely has a requirement that there engine can run on 87 (once ) without sustaining long term damage. We’ll probably never know for sure though.

Run 87 and you risk your car going POOF!!! No guarantee for it to blow right away of course, but you can pretty much guarantee to experience detonation. The only question is how long will the engine handle it.

EDIT: To add to this, with knock sensors and modern tech, the car does adjust accordingly, so I'm sure it does a decent job of lowering your power to prevent damage. It would certainly be a bad idea to push the car in any way when running on lower octane fuel.

[Tcoat]

Originally Posted by Transport3r

Agreed, but as @ZDan pointed out, someone will. Subaru likely has a requirement that there engine can run on 87 (once ) without sustaining long term damage. We’ll probably never know for sure though.

Somehow this went from "the car will do it but run like crap" to "it will blow up if you put one drop of 87 in".

If it has to pull timing and change fuel mix at the lower compression it will have to do even more at the higher. Pull more timing run even crappier.

[Quentin]

Originally Posted by Dzmitry

Run 87 and you risk your car going POOF!!! No guarantee for it to blow right away of course, but you can pretty much guarantee to experience detonation. The only question is how long will the engine handle it.

EDIT: To add to this, with knock sensors and modern tech, the car does adjust accordingly, so I'm sure it does a decent job of lowering your power to prevent damage. It would certainly be a bad idea to push the car in any way when running on lower octane fuel.

You can push all you want. The ECU will say, “Thanks, but no. Here is your 180hp (or lower) peak.”


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[Dzmitry]

Originally Posted by Quentin

You can push all you want. The ECU will say, “Thanks, but no. Here is your 180hp (or lower) peak.”


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Right, but the ECU will say this after there is some detonation - which could result in potential damage, but shouldn't I guess. I'm not very experienced on understanding the details in how quickly the ECU adjusts and whether it keeps the power low afterwards. My assumption would be that it always allows some detonation - quickly learns, and adjusts air/fuel and timing... then after some period of time it repeats this cycle, therefore always allowing some detonation to occur that could lead to some damage. Could be totally wrong.

[Transport3r]

Originally Posted by Dzmitry

Right, but the ECU will say this after there is some detonation - which could result in potential damage, but shouldn't I guess. I'm not very experienced on understanding the details in how quickly the ECU adjusts and whether it keeps the power low afterwards. My assumption would be that it always allows some detonation - quickly learns, and adjusts air/fuel and timing... then after some period of time it repeats this cycle, therefore always allowing some detonation to occur that could lead to some damage. Could be totally wrong.

Modern ECUs are extremely fast at catching detonation and saving the engine. BMW’s N54, their first DI Turbo I6, had a few aftermarket boost contollers introduced that would increase boost pressure only and let the ECU figure out the test. They needed some ‘adaptation runs’ IE let the ECU figure out where it knocks badly so it can adjust timing. Nowadays proper tuning solutions exist for that platform, but still, nobody blew a motor from letting the ECU handle knock control, even waaaaay outside factory parameters.