Regular v Premium Experiment

Actually Octane has nothing to do directly with power.

Higher octane rating allows the air/fuel mixture to be compressed more (variable timing, high compression pistons, turbo/SC boost) before spontaneously combusting (detonation), thus resulting in higher potential for work (power).

Put premium and regular in a 1974 350 chevy engine with 9:1 compression ratio and you won't see a difference. The confusion these days is with that many, but not all, engine management systems can monitor knock and a number of other sensors and adjust a multitude of other systems, boost/VVT/Ignition timing/etc... and potentially eek out more economy and/or power.

In short octane is actually how well the mixture RESISTS combusting (without an ignition source i.e. spark).

 

It's the "provided all things remain equal part"... as the numbers above do not reflect "equal". The 1GR numbers reflect that the ECU can run more timing without knock with 91 vs. 87.

Another way to think of it, with 87 when the spark ignites, you have an explosion, with 91 when it ignites, you have a slow burn of the fuel. Which one you think would push harder on the piston?

Before someone says it, yes, I know explosion vs. slow burn is pushing the story, but it's how I internalize the difference between octanes.

 

If this was true toyota wouldn't have put a line in their owners manual telling you to use higher octane for best performance. They took it out in the later years but I know it was included in at least the 05 and 06's.

 

Interesting experiment. You mentioned more power via the butt dyno with 91 octane than with the 87 octane. That begs the question, did you driving habits change with the 91 octane skew the numbers lower from a case of LFS, lead foot syndrome?

 

Explanation got buried in a later post... updated the OP with the summer/winter blend mpg so you can see the difference.

 

Are you planning any other experiments or have you done any experiments on cold air intake or exhaust modification tests on fuel consumption?

 

Nope. The CAI is a waste unless you wanna increase dB.

 

Very interesting experiment. I have only used 87 octane and only fill up with Shell and Chevron gas (mostly Shell) though because it's cheaper. I calculate my MPGs every time I fill up and with 87 octane Chevron I'm getting slightly better MPGs (18 with Chevron and 17 with Shell). On a side note, I have observed and recorded slightly higher MPGs in the mountains (driving at several thousand feet above sea level). Maybe it was the coasting down hill or whatever but my MPGs were definitely better in the mountains. Maybe someone could explain the effect of altitude on gasoline/engine performance

 

I run Shell V Power 93 Octane exclusively in my truck with no ethanol. I've never run anything else. Regularly get 22+ MPG. Not sure if it is worth it or not but it certainly doesn't hurt anything and as long as I can afford it I'll keep doing it.

 

I came across 1 station near me that has pure gas. He wants 75 cents per gallon more than 87. Forget that. Way too much out of my pocket.

 

I always run non ethanol 91 , V Power when I can get it ( no Shell local to me )

 

Or response

 

The way I understand it, since there is less oxygen at higher altitude, the need for fuel is also reduced. Therefore, better fuel economy. I noticed an increase in fuel economy after moving to CO from FL and also notice better economy when taking a trip into the mountains compared to the front range.