Does octane really matter?

[hand amputation]

Hello, I'm somewhat new here, so please pardon if this has been asked before.

I am so happy with my Sonic. I love almost everything about it. I came from a 2011 Chevy Silverado, 6c, regular cab. I really enjoyed driving it. It was BIG, the ride was smooth, and it looked great. I did NOT enjoy filling it up. My commute to work is pretty long, and I was averaging ~$300/month on gas. With my Sonic, I am averaging ~$120/month.

So, on to my question... Gas prices have come down a bit, and when you pair that with the smaller tank and better MPG, I have been hitting the '89' or '91' button at the pump, as opposed to the '87' with ethanol that I was used to filling the Silverado's MASSIVE tank with.

So.. does octane really matter? I feel good putting higher octane, 100% gas in my Sonic, but is this just a placebo effect?

Thoughts?

And thanks for reading this!

 

[Opticon]

In a tuned, turbo, high compression engine with an inclination to preignition? yes.

In a naturally aspirated car with stock timing? no.

 

[rdss]

Knowing if you have a 1.8 or 1.4 will help. But, I recommend running 2 or 3 tanks of regular through it and logging and then doing the same with 93 and deciding for yourself if it's worth the extra cost (if 93 balances out or is better, that's your choice...). If you're planning on tuning and the such running premium is a no brainer but if you're just commuting with the car I would run 87.

 

[hand amputation]

Thanks! (so far)

To be honest, I'm not sure if it's a 1.4 or 1.8, but it's an automatic, non turbo version.

 

[$ub$onic]

1.8.

Your fine with low octane.

 

[hand amputation]

1.8.

Your fine with low octane.

Well, that's good to know. I'll keep going with the 100% gas for sure, that's a whole new discussion.

 

[Larrymer]

If the car isn't tuned for it, don't use premium. Even if you have a 1.4L turbo. You're not going to see the advantage of additional timing/boost/mpg if the ECU tables aren't adjusted for it.

 

[River_Rat]

If the car isn't tuned for it, don't use premium. Even if you have a 1.4L turbo. You're not going to see the advantage of additional timing/boost/mpg if the ECU tables aren't adjusted for it.

Much of this discussion took place prior to your joining the forum, but it is pretty well established that the 1.4 has a "dual map" that does indeed take advantage of premium fuel.

A search for "dual map" should return substantial results.

 

[Larrymer]

I'd like to see some logs of octane scaler and timing advance on 87 vs. 93 then. I can't believe it would have been calibrated on the wrong gas and they just let the ECU optimize it. Not saying I don't believe you but that seems like a horrible way to do it.

 

[laborsmith]

It is a horrible way to do it.

It is done this way because the engine was designed for euro gas grades.

Most Americans who buy sub-compact cars will not consider using higher grades of fuel therefore the ecu is designed to adjust timing to the grade of fuel used.

This debate was carried out more fully with more threads in cruzetalk before the first Sonic rolled off the Orion Assembly Plant line. Chevy does not publicize this but its engineers have corroborated this. Long ago near the beginning of this forum I posted links.

Normally one gets no good effect when using a higher grade fuel then recommended.

Normally.

But in this case, the Sonic is not normal.

Once again, I will not do the search, having done it once and feeling no need to do it again, but if one disputes me searching will help find the info t either support or refute my statements.


Laborsmith

 

[Eric Smit]

as laborsmith accurately and concisely stated, it's how it is. there was a huge massive thread about it, continue the discussion there.

 

[Larrymer]

I looked around, didn't see it. Have a link?

 

[Scot]

So, being brief:

Most cars today have knock timing that can both advance and retard spark timing based on sensor feedback. Back when I was working on the Lincoln LS - we introduced knock-scaled advance to increase performance and fuel economy. In the simplest terms, there was a table of acceptable advance you could increase spark to and then it was compared to the MBT table and the lowest value won.

Looking at the way GM does their spark (HPTuners shows "Low Octane", "High Octane, and "MBT" spark tables) - I think it is similar.

 

[cndctrdj]

Octane makes a huge difference in how an engine runs and how it makes power. Whatever the car says to run. Always run that. If you have options. Then the higher the octane the better that car will run. Assuming you are within the cars designated setup. Like the sonic. If you run 93 instead of 87 you will make more power and get better gas mileage

 

[sx sonic]

Octane makes a huge difference in how an engine runs and how it makes power. Whatever the car says to run. Always run that. If you have options. Then the higher the octane the better that car will run. Assuming you are within the cars designated setup. Like the sonic. If you run 93 instead of 87 you will make more power and get better gas mileage

May get better fuel economy with higher octane on the 1.4t. In my numerous logs I've never noticed a quantifiable difference between fuel grades (87 vs 93 of the same supplier). Or even a difference after in mpg after numerous mods.

But as mentioned the 1.4t has the capability to utilize higher octane fuel. If it detects knock it scales the timing back (and then resumes conventional knock control) until the tank is refueled.