Horsepower and Octane

[MikeS.]

My wife's 2016 Mazda CX-9 computer reads octane and adjusts horsepower. It is advertised as 250hp on premium and 225hp using 87 octane. If the ST gets 400hp/415tq on premium, are the hp/tq numbers using 87 octane advertised anywhere?

 

[zdubyadubya]

its not a consistent number and depends on how the IAT spark table is set up as well as intake temps and MAT calculations. I would say that 20-25hp is probably a pretty good estimate though from what i have seen from 93->91 so 87 obviously will be a bit more.

 

[Lightning Struck]

It doesn't "read" octane. It just listens to the knock sensors.

 

[Blown F-150]

There are a lot of factors like elevation and ambient temp. The Wife’s ST reads 94 octane as 95.3 in the fall temps, but settles around 93.1 in the middle of summer.


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[TMac]

There are a lot of factors like elevation and ambient temp. The Wife’s ST reads 94 octane as 95.3 in the fall temps, but settles around 93.1 in the middle of summer.
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Just curious, where do the readings come from? Logging via the HP Tuners App? I wouldn't think elevation or ambient temp would affect actual octane ratings, so is this number an "effective" octane number? Second, due to seasonal variations in ethanol, wouldn't this also affect the readings?

 

[Blown F-150]

Yeah, this is based off of the “inferred” octane channel in the VCM scanner.

I 100% agree that there can be variations in fuel quality seasonally and would be a factor.

However, we see some crazy temp swings and I log almost daily. I’ll see a variation with the inferred octane on the same tank of gas.

So, just assuming here, but it seems like spark and OAR or LOR have some impact on that calculation.


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[CareerFiremanGuy]

reviving an old thread with some info ...

When Ford released the Coyote engine in their 2011 Mustang, they said it made 412 hp on 93 fuel, 400 hp on 87. With turbo engines the loss is generally higher.

Witness C&D's 2019 test "Is Premium Gas Worth It? We Test High Octane on 4 Popular Vehicles." With an F-150 Limited 4x4 powered by a 450 hp 3.5 L twin turbo, it made 360 hp at the wheels with 87 octane and 380 hp at the wheels with 93 octane (that's ~25 hp at the crank). I'm sure my dealer filled up my ST with 87 octane when I picked it up, so seeing how the owner's manual says to use 91 "for best performance" as soon as I'm down to 1/2 a tank it's geting topped off with 93.

Just FYI.