Turbo on 87, 91, 93 Octane - All or nothing?

[hal2]

So we know about the Turbo's HP/Torque rating at what Mazda refers to as regular/87 vs Premium/93. Do we know if it needs 93 to get that additional power? Meaning no incremental increase at 91, but rather it's all or nothing and needs 93? - in other words, no increase realized at 'only' 91 octane?

We have all read the same articles from Consumer Reports and others about premium gas for decades. I hope this doesn't devolve in to questions about octane that I am not asking. I can't stop you, but please let's not go off the rails with info on octane, knocking, predetonation, waste of money, engine 'learns', modern engines, as well as other non sequiturs, but rather remember this turbo actually is engineered to provide different output based on octane.

Just the simple question, all or nothing from 87 to 93, or incremental gains at 91?

EDIT: Oops, I think I posted the same question weeks after I bought the car.

 

[DwightFrye]

This has been discussed before, I think it is something like 3 to 4 HP gain for every 1 point increase in octane. I can't get 93 octane here in California but figure with 91 octane which is my fuel of choice in my turbo CX 5, I am getting about 245 HP give or take. Close enough for me.

 

[sm1ke]

This has been discussed before, I think it is something like 3 to 4 HP gain for every 1 point increase in octane. I can't get 93 octane here in California but figure with 91 octane which is my fuel of choice in my turbo CX 5, I am getting about 245 HP give or take. Close enough for me.

Yep, what Dwight said. I can only get max 91 here and I spend enough time above 4k to notice a difference between 87 and 91. Another user even went as far as timing a few runs on 87 vs 91 and came to the conclusion that it isn't "all or nothing".

 

[Odrapnew]

My guess is that the ecu plays with timing and 'watches' for knock to provide the most timing with the given fuel. So, i would also expect incremental changes with octane between 87 and 93.

 

[markjenn]

Discussed in other threads. Since running an engine right at the edge of knock all the time is tricky and potentially has long-term durability concerns, it’s not typically done. Instead the engine is run in a fixed state of tune that produces full power except when knock is detected in challenging conditions - high ambient heat, heavy loads, and high boost at high-RPM. If you’re running 91 (or 93), you’re much less likely to get knock in these conditions. Mazda’s derating is just an average thing to reflect an increased risk of knock on lower-octane fuels.

So running 93 over 91 probably just increases the likelihood you will continue to make 250-hp under all conditions rather than making more than 250-hp.

Wish we had some dyno tests where engine could be switched back and forth on different octane fuels while running. But that would be a ton of work/expense.

- Mark