Octane

3315 Views 11 Replies 11 Participants Last post by Bikerbob951, May 4, 2011

Papasmurf

Discussion Starter · Apr 1, 2011

What octane are you guys youing at the pump? I was wondering if different octanes give better gas mileage in the 2.0? I'm using 87 right but was going to try 89 to see if there is any difference.

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Higher octane will not net better gas milage. The higher the octane in the gas the more energy needed to ignite it. The reason for running higher octane would be to reduce detonation and knock in an engine. The engines in the Forte do not require higher octane and running it will have no benefit unless heavily modded.

Now enter the naysayer who swear by the BS they hear from their "sources" or their own "experiements".

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tpkoup

· #3 · Apr 1, 2011

sje0123 is spot on. You would only use higher octane fuel to ensure that the fuel does not ignite out of the expected engine timing. Higher Octane fuel is actually more stable and thus more important for high performance engines.

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AZMX5

· #4 · Apr 1, 2011

I use premium in my other only because the timing and design of the spark calls for it. I actually do get a bit better gas mileage but that is not due to it's octane level, it's because the engine is designed for it.

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reza_ibiza

· #5 · Apr 25, 2011

Because of the 10.5:1 compression ratio, it seems to be better using higher octane like 91 not 87 avoiding knocking!

87 is good for 10:1 or less

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patyouknow

· #6 · Apr 25, 2011

87 all day.

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Joechicklets

· #7 · Apr 25, 2011

Already a thread about this. using regular is just fine and dandy

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arinesmith

· #8 · Apr 25, 2011

+1
I run 87 all day everyday.
Did one tank on 92 and got worse mpg.

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reza_ibiza

· #9 · Apr 25, 2011

It is not possible! Technically more octane means higher potential restistance of soon combustion at high compression engines. It means if your engine is in high compression and use low octane gas, it will burn at sooner time, before sparks burn! and it will knock your engine and make less MPG and big failures on the engine in long time. But in vice versa, if you use more octane than the requested, it will not harm your engine and make no lower MPG. It will be just waste of money. so your lower MPG with 92 was caused by sth else, not gas!!!

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reza_ibiza said:
It is not possible! Technically more octane means higher potential restistance of soon combustion at high compression engines. It means if your engine is in high compression and use low octane gas, it will burn at sooner time, before sparks burn! and it will knock your engine and make less MPG and big failures on the engine in long time. But in vice versa, if you use more octane than the requested, it will not harm your engine and make no lower MPG. It will be just waste of money. so your lower MPG with 92 was caused by sth else, not gas!!!

Most of this is correct, but the biggest thing is that if the engine is not tuned to run whatever grade of fuel you are using, you will lose efficiency / power regardless. Think of it like this:

The engine in your Forte is designed to burn 87oct at an efficiency rate of, let's say, 90%. Meaning, that 90% of the fuel is used to create usable energy in the purpose of moving you forward. As it was mentioned in an earlier post, it takes more activation energy (i.e. compression and spark) to completely burn higher octane fuels. So, if we put 93oct in an engine designed to run 87oct, we will only see about 60% of the fuel converted to usable energy. This does two things, 1st: creates richer emissions. This reads on the O2 sensors, and the car will try to correct that by adjusting air and ignition timing. Neither of these will really change the efficiency of the burn, since the fuel grade is the variable here. 2: since the engine is not running at peak performance, you'll have to apply slightly more fuel than normal per driving scenario, thus raising your consumption, and lowering your MPG.

Bottom line is fuel burn efficiency; 87oct burning at 90%, or 93oct burning at 60%

I hope that all makes sense to read

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