High octane gas

Haven't researched it, but I've always understood premium gas to require 10% more crude to make (partial reason for the price difference). IMHO, I'd say you weren't doing the world, or your wallet, a favor by using high octane unnecessarily.

 

I know I am reviving an old topic here, but...

The "buy 87octane" vs. "buy 93octane" battle has been going on for some time now. I am personally in favor of using higher grade fuels.

I was hoping to find some strong evidence to support either side of the argument here in the forums, but haven't had much luck so far.

I will post any useful sources I find in the future here in this thread, and hopefully others will do the same.

~Andrew

P.S. Finding VALID evidence on this topic can be difficult especially on the internet.

 

Several good reasons not to use 93 octane gas in your Prius:
1. Owners manual fuel recommendations
2. Gas Price differential between regular and premium
3. Higher octane is intended for higher compression performance engines, not exactly the Prius engine

That's all for now, Andrew. Save your money and stick to regular gas!

 

Thanks for the advice randalla.

But I'm still a bit confused...
You say that higher octane should be used in performance cars with high compression ratio motors.

Please correct me if I'm wrong, but it's my understanding that the Prius has about the same compression ratio as a Lotus Elise. Yes I understand that it is designed to run on multiple octane ratings of fuel, but I still believe that my injectors stay cleaner when I use 93 octane, which translates into better fuel economy.

I guess the real reason I buy the more expensive stuff is because I like to show-off my high MPGs.

I just googled the compression ratios of both the cars I mentioned and this is what I found...

http://motortrend.com/roadtests/alternativ...rid/index2.html
http://www.csi-auto.nl/carview/lotuselise.htm

...Prius compression ratio varies with valve timing.

(Ending post before I start to ramble.)

~Andrew

 

Actually,

As mentions in other threads several months ago, higher octane actually has less energy in it than the lower octane. All grades of gasoline now contian detergents that are designed to keep injectors clean. As randella pointed out the Prius is designed for 87 Octane and I doubt that over several tanks that you would notice much difference in any case. Ambient Temperature will have a much greater impact.

Certainly, there is no harm in using the higher octane (or at least, I doubt it) with the possible exception of the additional drain on ones wallet. My wife actually insists on using 10% Ethanol mix year round which one of our stations locally carries to further reduce emissions which does add a few cents on top of the 87 octane.

Jon

 

Using high octane gas in your Prius is simply wasting money. According to the Magliozzi brothers, most people who are using high octane do so in the unwarranted belief that the car will perform better, but, UNLESS the manual specifically states the need to use high octane you should use regular. They elaborated on this theme on one of their programs: a given gasoline engine can only absorb a given amount of "energy potential" in the fuel used. Any potential beyond that amount is simply blown out the engine, more or less unused and thus wasted. These are my words, but the gist of the explanation is theirs.
Another analogy is the use of vitamin C. Your body can only absorb a certain amount of vitamin C; any doseage above that ends up in your pee.

The ICE in the Prius runs at a near constant rpm, or within a much smaller rpm range than the engines in conventional cars, meaning that the ICE is subject to less stress. From what I gather, the higher octane fuels are required for engines needing much higher power output than the ICE in the Prius.
Bob

 

My aftersales service guy said: " As usual for Toyota cars we recommend first 3 tanksfuls of 98 [RON] gas (US 94 PON) and then switch to usual 95 [RON] (US 91 PON)."

RON-MON-PON gas rating conversion here

Hey, we're using *higher grade* gas as *normal* here in Switzerland as we don't have anything lower than 95 RON.

Now about premium gas benefits:
1. It's cleaner (sulfur, benzoates etc.)
2. Slightly better performance.
3. No tangible effect on economy.

 

Thanks for the info Jon.

Where and which brand station carries the 10% ethanol mix? I'm kind of curious about this (certainly going to start some research).

You are right about ambient temperature. Cold days means that it takes longer to warm the catalytic converter and all the components for that matter. Timing is altered to heat the motor up more quickly.

I also believe that cold air makes motors burn more fuel (which is great for performance but not so great for fuel efficiency). Cold air is more dense than warm air. More air means more fuel. More of this combination means more power.

(Wow I'm good at getting off topic.)

I was also wondering which thread it was where there was talk about the amount of energy in various grades of fuel. I would like to know more.

Thanks again everyone.

~Andrew

PS. I did mention once in another thread how they have higher octane fuels over-seas. Any comments on this (specifically on RON-MON-PON)?

 

SparkyMarvin,

Just did a search using the word "octane" alone and then with "and 87" and came up with several threads that contain the info that I was talking about. One is carried from the bottom part of page 1 through the 1st half of page 2 of the "Oil Change" thread. Another is the "Adding Napthalene..." thread. There are links to "Car Talk" with Tom & Ray as well as The Federal Trade Commission. While we all have our own opinions, certainly those 2 citations are worth much more.

As to the year round 10% Ethanol mix. Here in Idaho there is a local distributor called Stinker's (Skunk Logo) that sells it in all their fuel grades year round. They all seem to sell a Sinclair product but with the 10%ethanol added. About New England, I am back there most every fall for a few days but am not aware of anyone selling ethanol blends there year round. If you look in your manual under fuel however, you will find that Toyota actually recommends using the 10% Ethanol blend. I know because I lost that argument to my wife!!!

Jon

 

the info on the prius compression and valve timing makes me wonder (in my usual not-that-technically-well-informed way) if there will be ways in the aftermarket of adjusting the valve timing to get more power out of the engine

 

You are talking about two different animals here. The Lotus runs on the OTTO cycle, the Prius on the Atkinson cycle. The Lotus is a static compression ratio. This cannot be compared to the "expansion ratio" achieved by the Atkinson cycle engine.

Octane is the measure of resistance to detonation. Higher octane results in more power when the application is designed for it. In a high compression engine, higher octane is needed to prevent the fuel/air mixture from igniting from the heat generated during compression rather than ignition from the spark plug. Excess octane does nothing, since the energy available is little changed from lower octane fuel. However, under higher compression, more power can be generated as a result of the expansion of the ignited charge. Unless the ignition timing is automatically advanced by the engine control computer to take advantage of the higher octane, again no power gain exists. The Prius is designed to run on 87 octane fuel, (R+M)/2 method. Higher octane will not derive any benefit as the engine is not calibrated to take advantage of it, and the Atkinson cycle effectively prevents it.

 

Thank you mdacmeis. I agree with most of your technical insight, but am going to be stubborn and keep on buying higher octane fuel. Sorry.

And also a thank-you to jchu for such a speedy response. I don't have a wife, but my girlfriend always used to win our arguments.

~Andrew

 

I believe you'll find there is a TSB out on the Prius about this.

The Prius is definitely designed for 87 Octane, and in fact higher octane can trigger a "Check Engine" warning code which is really an emissions alert.

I'll see if I can find the reference document.

Edit: I can't find the Toyota Reference, but I did find someone explaining the rationale. Apparently 87 Octane burns hotter, and is necessary for the complete functioning of the Emissions System (all those catalytic converters I guess). So, it seems that you would actually be producing MORE emissions by using higher octane.

 

I used 93 for first 4000 miles and decided on trying out the 87. I heard no additional noises coming from the engine(when its running) and my mpg's have increased( probably because of the breakin process though...). I'm at 5200 miles currently running at 52.4mpg's. not much help here i guess...i'm out!

 

I am not a mechanic, but from what I remember from my tinkering days (when you could tinker with cars), is that higher octane burns slower, cooler, and with less energy. In the old days of carburators, as the car aged, it started to knock because of clogged ports and the gas burning at the wrong time because it couldn't get into the chamber fast enough. Instead of taking the engine apart to clean it, you would use higher octane fuel because it burned slower and cooler, allowing a longer burn time, spreading the burn gently over more of the stroke to get some usable power back instead of a fast hot burn slamming the piston at the wrong time. I could be wrong, but that's what I remember.

What I do know is: unless an engine is designed for hi-test, DON'T use it. Especially with these computer controlled jobs today. If the computer hits the spark, and the spark doesn't light it up because the gas is the wrong octane, that just sounds like trouble.

 

Even if higher octane fuel causes the emission control systems to not reduce as many tailpipe emissions, I still believe it helps to preserve the life of the car's systems. I guess maybe I'm trading cleanliness for lifespan, but I hope that isn't the case.

I would also recommend that everyone reference page 202-204 in your owner's manual. It says things like...

"Toyota recommends the use of cleaner burning gasoline and appropriately blended reformulated gasoline. These types of gasoline provide excellent vehicle performance, reduce emissions, and improve air quality."

"Select unleaded gasoline with an octane rating of 87 (Research Octane Number 91) or higher."
I'm taking this to mean that the emissions and car longevity research done by Toyota was done with 91octane fuel. Please correct me if I am misinterpreting this information.

Please remember that I realize I'm being stubborn and not making the switch to 87, but I would still appreciate any incite into this topic.

Thanks,

~Andrew

 

As to the "cleaner burning gasoline and appropriately blended reformulated gasoline" that Toyota is referring to is those blends that include any number of things such as 10% ethanol or that "MT..." stuff that California requires to reduce air pollution but is getting spilled into reservoirs from water craft causing its own environmental hazard, rather than Octane. The manual in the same area repetely recommends 87 octane... But Hey, It's your dime. :mrgreen:

 

I do not know, if high octane gas means the Catalytic Converters don't heat up enough, they may not burn things off properly and gunk-up, which would not be in keeping with 'preserving the life of the car', hehe.

The consolation there is that there's a pretty long federally mandated warrantee on Primary Emission Components.

But, even if they only gunk up a little, you'll still have increased back-pressure which can lead to other problems.