Octane v. torque/horsepower

[DAC17]

Been thinking about this for a while, and can't come up with a good answer, so I'll ask the experts.

I have a 2016 Ford Escape 2.0 Ecoboost. The owner's manual says that regular gas (87) is allowed, but that there will be additional HP with higher octane gas. Additional reading I've done suggests that, although HP goes up with the higher octane (say 93), there is no gain in max torque. My question is why does the torque rating not also go up with 93? I would expect that the torque at 87 would suffer accordingly, especially since the engine would be at lower (potentially more stressed) RPM's when the max amounts would be achieved.

Can anyone explain this in fairly simple terms?

Thanks much.

 

[Lyman]

The only way to see what is really going on with different octane fuel is to put it on a dyno. Generally you want to run the lowest octane that doesn't retard timing or bring on pinging.

 

[eljefino]

Maybe you actually do get more torque but the owner's manual is written for idiots.

The knock sensors I'm familiar with get ignored by the PCM at higher revs (say, 4500+) where you'd make "HP." Though they're always making them better.

 

[stranger706]

Max torque is still the same, but the torque curve is not flat on 87. On 93 the torque curve is flat from 2000 - 5500 rpm.

 

[BrocLuno]

You, all about ECM adjusting the spark timing. Might be more HP, but is it where you can use it easily, or at the top of the RPM range ...

 

[sciphi]

The computer makes an artificially flat torque curve so the car is more predictable. Without the computer running interference, the torque curve would be peakier. Non-car folks don't appreciate their sports drink spilling on their smartphone when the turbo kicks in at 1800 RPM or whatever it's fully spooled at.

Higher in the rev range where peak HP is made, the engine can advance timing or more likely lean out the mixture. Modern gasoline turbo engines throw away quite a bit of fuel when running 87 octane to lower combustion temperatures. That prevents predetonation. The higher octane means the computer can safely lean out the mixture, so more HP results.

 

[ZeeOSix]

Higher octane fuel will allow the engine to advance timing more, and that ends up giving you a little more power on the top end. If lower octane fuel causes ping/knock, then the engine cuts back the timing and that reduces power. Only time you might see more power while using higher octane is under heavy load/wide open throttle conditions.

 

[TiredTrucker]

And many times, the power difference is single digit spreads. Hardly worth considering.