88 vs 90 octane

There are lots of threads about this topic, the recent one is here.

 

I am currently doing a test on this with my 2013 prius c, in oregon we have 10% ethanol in our gas. The regular is 87 octane and premium is 92 octane where I get gas. I have tested with running full tanks of one then switch to the other and run a full tank of that. In this way I reduce the effect of temperature and weather on the results. after 3 tanks of each I think the difference is about 15% in favor on the 92 octane. the price difference is about 5% so the 92 octane is well worth the money.

most people say they see no improvement or little improvement and find it is not worth the extra money. My driving is mostly city, so that may explain the difference, who knows? I would advise you to try both and see for yourself. If you do please post your findings on 87 vs 91 octane in prius c, it is under fuel economy section for prius c.

update on mpg
tank in feb. 87 e10 gave 52.9 calculated at pump
tank in mar 91 e10 gave 59.6 calculated at pump (11% increase)
tank in april 87 e10 gave 57.1 calculated at pump (4% decrease)
tank in may 92 e10 gave 67.7 calculated at pump (15% increase
tank in june 87 e10 gave 57.81 calculated at pump(15% decrease) I forgot to log this when I filled up it is on fuelly
tank in july 92 octane e10 78.5 mpg driving for the best mpg I could get not good for compairson of the octane effects for mpg

 

The over-simplified answer is all gasoline is equal so don't bother with 90.

The complex answer is there could be energy content differences, and the 90 might have more energy (and it also might not). Depends a little on where you live in Texas. I am looking at the USA map of gasoline requirements, Houston and Dallas are the two regions using EPA reformulated gasoline (RFG). EPA RFG essentially requires a lower energy content (for clean burning purposes) and no significant energy content difference between Regular and Premium.

If you get outside a RFG region, then there is good possibility the 90 has more energy content and a little better MPG. Whether or not it is worth the higher cost is questionable. Also non-RFG regions tend to have more E0 availability...again the extra cost for E0 usually cancels out any benefits.

 

Dr. House uses premium fuel!

 

Dr. House is fiction.

Just like any benefit you'll derive from using 'premium' gas.

 

It was a joke!

Have you done testing to dispute my fiction? If not, how do you know its fiction?

 

It's fiction because I watch him on TV. (Note: I know you meant the fuel.)

 

My results are not fiction. I believe many will get good benifit from higher octane.

 

There's an acronym in the automotive industry that's causing people to spend a LOT of time doing a LOT of research in increasing their Corporate Average Fuel Efficiency. (CAFE)
Perhaps you've heard of it.
Maybe not.


If Toyota could amp up their fuel efficiencies simply by putting a sticker on their car that says "Premium Unleaded Only" tell me why they would not do this!
I'll betcha my CPO coin that if Dodge could increase their truck and sports car laden fleet by even a third of your "results" simply by adding a few stickers to their cars and changing the owner's manuals they would be allllllllll over it like a bum on a bologna sandwich!

Your results may not be fiction, but your results may also not be simply based on whether or not you overpaid for your gas.

My Prius is a company-supplied car.
One time I "accidentally" put Premium in the tank.

This resulted in 2 things:
1. An email from the head-shed reminding me that I'm not supposed to put Premium fuel in their car.
2. About the same fuel efficiency as I've seen in all of my other tanks.

That's not fiction either.

 

^^gaso does not have a spec for energy content so it varies but if you happen to live in an area where your premium has more energy content you might see a benefit, which in defense of the bean counters probably does not pay out

PS- EPA does CAFE MPG testing with a very high energy content E0 premium fuel and then uses factors to convert to E10 and so on

 

Try going back to regular with your next tank, maintain your "driving for best mpg" style, see how that goes? I've got a feeling the improvement is down to change in seasons coupled with you're driving more for mpg, not to knock it.

 

But then shouldn't June have been closer than 15%. Yeah, some of it might be placebo, but 15% is a lot. March to April is more what I expected.

 

Simply put, a higher octane number fuel can withstand a higher compression before detonating. So only an engine that can benefit from this characteristic will see improved performance.

 

I'm having a hard time believing any Prius C will see improved mpgs with pure gas 91 octane v. pure gas 87 octane. I've gone back and forth between the two for two years in my C and have found absolutely zero difference in mpgs between the two.

My Z28 gets better mpgs with 91 or better octane, but it's a higher compression engine and is designed to take advantage of the higher octane. The Prius C is not like that, so see's no advantage.

Besides, even if you are in a car that does get better better mpgs, you're paying more for your gas. It's a wash. No point unless you're getting longer black strips from punching it, and you aren't going to do that in a C!

 

OP Michael, welcome to Prius Chat!

There is little here that hasn't been asked already 20 times, so if you have a questions you should try the search feature.

 

The Prius C runs well on 87 octane and generally gesno advantage from 91 octane. The reason is the recipes for the two grades ofgas may vary enough to let the higher octane have higher energy chemicasls ( gasoline is a large mixture of chemicals gained from crude oil). In TX that can have a measureable difference but in most places, especially where specific recipes are required the energy difference is no where near the increase in cost.
This advice from an od refinery engineer is just make sure you buy 87 octane from a brand dealer.

 

How did you measure mpg? by how much it took to refill the tank? Thats not an accurate way to measure mpog. You have to determine a refill mark and measure the amount to fill to that mark and divide the mileage driven since last refill to the current one.
It is a difficult task to get accurate mesurement.

 

For a single tank, if your past behaviour (for example) has been to fill 'til it first clicks off, and you fill it by that method, and do the math with distance travelled, you'll at most have minor inaccuracy. Repeat that for a second tank, and a third, it's going to be pretty deadly.