mpg with 91 vs 87, in your prius c

I've been to stations alone I-90 which dispensed E85 and gas from the same nozzle, 4 grades. And can you be so sure E85 isn't getting occasionally transferred from one tank to another?
All this is a moot point: gas differs in E content, and in some locales it can contain 20% ethanol or more.

 

Not sure if it's just in Canada, but Chevron (and some others?) offer ethanol-free gas, in highest octane only.

 

I am sure that further "discussion" with you about this is pointless.
You win. I quit.

 

Haven't realized we were playing for something?

Just passing my experience. Almost cost me an engine, and time baby it to honest gas station.

 

It's a little different...most of the majors here have mandates to blend 10% ethanol to meet quotas.
Also many major city areas have E10 mandates.
So if you get away from the major metro areas, you can find some E0 in various grades, usually from smaller gaso companies.

 

Have we not had this exact discussion before ?
And have you ever answered the question of how much of that "premium" you were using was ethanol free ??
Your 14% figure is so far off from what the engineers say and other owners experience (both ZERO) that it cannot be accepted without comment.

 

@rider: he probably means he needs 14% to break even on cost.

Out of curiosity: "C" is equipped with knock sensor, right? High compression engines with knock sensors usually get better MPG on premium...

 

I assume it has one but don't know for sure. Even if it does that is only half of the equation.
The other part is the max. timing advance allowed.
Anyway, spark knock and compression knock are two different things; same result, just different causes.

NONE of the Prius engines and probably none of the Toyota engines in general can properly be considered "high compression".
If there really was anything practical to be gained by using a higher octane fuel, Toyota would be shouting it from the rooftops.

 

"C" has 1:13.4. Highest of non-diesel sold in US

 

I am not an expert on engines, but I've never heard anyone here say that the c is able to get better MPG with Premium due to the higher octane.

I do think the energy content of gasolines can vary (eg; E0 vs. E10), and my understanding is when EPA does MPG testing they correct for energy content before reporting MPG to the public.

 

Not sure if EPA does such thing. I remember reading Chevron bolster about big 3 trucking their gas across several states to Detroit for EPA tests. That was many-many years ago; thing change over time.

From what I see so far "C" MPG is worse than Gen3, but there's too many factors to call it. I'll test 87 vs premium after break in. Since our gas is E10 across the board, E content will not be a factor.

 

It's also same energy content, if not a little less for the Premium here, so it'll be an octane test for sure.
Just remember the summer fuels change comes in and changes things a little. Try to do your test before or after that change.

 

That another factor. How much of what fuel in the fuel? with the switch to summer fuel staged btw March a d June 1st...

Looks like the best time to check is in Feb and August. But my "C" is still too green. Plus in general C seems to be more sensitive to temperature, so Feb might be the best time

 

According to one car-expert in a documentary on gasolines, knock-sensors make using Premium gasoline unnecessary in most cars which specify using it.

 

Unnecessary maybe but that's different than "undesirable".
In a car designed to use higher octane fuel, you are almost always better off to do that.
If you drive hard, more power.
If you drive easy, more mileage.

 

Opinion_noted.

 

generally that is true, however, we are finding 91 octane gas typically has less contamination with ethanol and less energy components so 91 can give better mpg. it has nothing to do with octane rating as it is the result of recipes that have more energy. we've had the opportunity to test both non ethanol vs ethanol up to 10% and the diff about 5 mpg in favor on non ethanol mid grade gas. its faster on track too, adding 2-3 mph at ends of long straights. the recipes for gas, which generally has a multitude of compounds, will yield different mpg from the same pump week vs week. no, not in same day generally, just after another delivery.

 

take it from a crowd with vettes, jags, vipers and such, those knock sensors are absolutely necessary. gas varies that much. that is an expert opinion from a vehicle and petroleum engineer.

 

you can rest assured that 91 octane will not be cost efficient on any engines designed to run on 87 octane gas though sometimes 91 will yield better mpg and power. its never enough to pay for the extra cost of gas.
engines with high compression ratios that require higher octane should use the 91 octane stuff and not depend on knock sensors to dial back the spark advance enough. it used to be pretty consistent that CR's over 9.5:1 required 91 octane but many of todays engines withspecially designed combustion chamber will tolerate octanes of 87 above 10:1. mazdais a good example with skyactive designes and computer trickery.