Just filled up the tank with 91 octane premium fuel

[427chev]

Originally Posted by BLAZINBLUEVITZ

NO, your just a latecomer who thinks their gonna teach someone something with their knowledge. Maybe if this wasn't the 56th thread of the same topic id be a bit more receptive......

I have nothing to "Teach" anyone on this board.

Rather, I prefer to ignore children who have no understanding of the related science and will therefore remove myself from this thread.

[DerFlosser]

Originally Posted by 07WYarisRS

Higher octane does NOT have a cleaner ignition
Unless the compression is high enough to take ad vantage of the fuels flash point, burn rates and flame front speeds the engine will not burn as efficiently a a low octane and you end up with carbon deposits.
Lower octane fuels burn cleaner and more efficiently in ANY lower compression engines.
but I just build performance engines for a living and actually test them using the proper equipment..WTF would I know about fuels and the affects right?

Don't confuse RON and PON people
A 89 RON octane rating is PON (pump octane rating) of 86
when you look in the manual and see a research octane rating of 91 that does not mean to use 91 pumop octane... 91 RON = 87 PON.
Toyota, Honda and most other companies build thier econo engine to run on RON 89 (pump octane 86) because thats whats all thats available in some counties for low octane and it makes these engines most cost effective...

I'll never understand people that buy one of the cheapest econo boxes on the market and then run it on high octane ... you guys are nuts lol
you guys much know more then the dudes in white lab coats at toyota

I am not disagreeing with what you are saying. My point is that it's possible for the car to start smoother due to the higher octane fuel because, even though you may build engines and see drastically higher compression motors, 10.5:1 is still a "high enough" compression ratio to see benefits at start and idle condition utilizing a better grade fuel. I am not saying to run the car with the higher octane fuel...I am merely saying that it is a good possibility that the feeling is real in regards to the smoother start.

[Aothachos]

DAMMIT DARKMOON87 look wat you started lol, this is going to be the hot topic of arguments, like i said I know what i feel with 91 octane and I'm not changing, i don't mind putting in extra couple dollars for better fuel =)

*better fuel* watch someone say something about that lol

but yea im not convinced to switch to 87 so =) LET THE DEBATE CONTINUE!

[nerp]

All octanes have detergent in them. It's a bit of a misnomer to say that using 93 octane will "clean out" an engine that normally requires 87.

[07WYarisRS]

Originally Posted by DerFlosser

I am not disagreeing with what you are saying. My point is that it's possible for the car to start smoother due to the higher octane fuel because, even though you may build engines and see drastically higher compression motors, 10.5:1 is still a "high enough" compression ratio to see benefits at start and idle condition utilizing a better grade fuel. I am not saying to run the car with the higher octane fuel...I am merely saying that it is a good possibility that the feeling is real in regards to the smoother start.

DETONATION...look it up
thats the ONLY reason to use a higher octane fuel...
thats why we have higher octane fuels, not because they can give better mileage or make the car run smoother or start easier... Fuels DONT WORK THAT WAY
Higher octane is available at the pumps because some engines are forced induction, some engines run high compression ratios like todays modern Super sport bikes and off road bikes. Even some of these engines running 12.5:1 compression only require 87 octane

I hear what your sayin...
I'm just sayin NO, its not possible to start easier. Besided the compression ratio there is compression rates and HEAT... you need to calculate the HEAT of combustion into that mix... sure the lil yota engine may be a higher compression ratio then many other auto engines but at 10.5:1 there is not enough heat and compression at start up to take advantage of the higher octanes higher flash point..
My cammed Suzuki GSX750F pushes 100 hp runs 11:1 compression and redline of 12,000rpm and only needs 87 octane... Do you really think the Yaris needs better fuel then my crotch rocket?

Like i said it all has to do with the fuels flash point, the lower the flash point the easier it will ignite, the higher the flash point the harder it is to ignite.
Thats why many bio deisel set up have a deisel start because the biomixtures like used engine oil of veggie oil often has a much higher flashpoint and is harder for the engines to start on them. they start on the diesel and then switch over to run on bio once warmed up.

With higher octane fuels they not only have a higher flash point making it harder to ignite but they also contain additives that eliminate or remove free radicals in the fuel that can promote detonation. While the actual burnt temp of the fuel may not be changed the flame front speeds can be altered or slowed to help eliminate detonation. If you engine has no detonation, then there is NO benifit to running higher octane fuel... NONE

people often think higher octane fuels burn hotter and faster then lower octane fuels... this is a myth, actualy the lower the octane the faster it ignites and can burn faster depending on the additive and free radicals in the fuel..
If you were to take a carbed engine with fixed timing and diid two runs on a dyno one with 87 and one with 91 octane fuels. the 87 will always produce more HP and higher EGT (exhaust gas temps) then higher octane fuels...

Do you know why it feels smoother on higher octane fuel... they call this soggy. When an engine is jetted too rich or running too rich it has a soggy feel to it. An engine that is running a little to rich will run awesome, but it lacks power. the richer it is the less power it makes. And ebgine running leaner produces more power, too lean and you start to run the risk of overheating and detonation and pre-ignition ( not even close to the same thing bTW)
When an engine is running efficiently it can have what is known as spark knock or PING under heavy loads, this is normal but the more efficiently the engine is burning the fuel and the more power its making the less smooth it can feel.
Thats why racers often say the engine is a little lazy or soggy feeling when running rich or loading up. This is usually caused by an eninge that only needs high octane pump fuel but is being run on race gas.

[The little red pill]

. . . . . ouch . . .

[427chev]

Originally Posted by DerFlosser

I am not disagreeing with what you are saying. My point is that it's possible for the car to start smoother due to the higher octane fuel because, even though you may build engines and see drastically higher compression motors, 10.5:1 is still a "high enough" compression ratio to see benefits at start and idle condition utilizing a better grade fuel. I am not saying to run the car with the higher octane fuel...I am merely saying that it is a good possibility that the feeling is real in regards to the smoother start.

Nothing you said makes sense.

First of all, small chambers (inherent to a small displacement engine) are more efficient than larger ones because flame propagation occurs over a smaller area. That's the main reason that motorcycle engines are able to run such lofty compression ratios.

Secondly, the Yaris is one of the few engines that offers DIRECT INJECTION - which cools the intake charge and as discussed in the following link:

http://www.greencarcongress.com/2009...portfolio.html

10.5:1 is not a high compression ratio for a modern, direct injected, small displacement engine. The 2.4 liter, direct injected GM engine discussed in the link above runs an 11.4:1 CR!

Hence, the 10.5:1 compression ratio in the Yaris engine (where each cylinder represents a mere ~ 0.375 liters and where direct injection is involved) isn't comparable to an engine that utlizes port injection and larger cylinders (particularly the bore dimension).

What amazes me about these bulletin boards is that people voice opinions without having any REAL understanding of the subject matter, most of which boils down to advanced engineering principals.

There is absolutely, positively NO EMPIRICAL EVIDENCE supporting the notion that any modern engine that has a recommended fuel octane rating of 87 PON can, in any way, benefit from a gasoline of a higher octane rating. If anything, empirical evidence suggests the opposite, since the slightly lower burn rate of the higher octane fuel may adversely impact the intended timing of the complete combustion process, relative to the position of the piston and the valves.

[jambo101]

Well said 427chev,i think most people fall into the marketing hype of naming the higher octanes with such colorful names (Super,deluxe,Premium,Gold etc)as to make 87 octane seem inferior,so they only fill up with that superior high octane and talk themselves into believing that they are somehow getting more power and better fuel economy without ever doing any meaningful measurements of whats really going on .

[DerFlosser]

Originally Posted by 427chev

Nothing you said makes sense.

First of all, small chambers (inherent to a small displacement engine) are more efficient than larger ones because flame propagation occurs over a smaller area. That's the main reason that motorcycle engines are able to run such lofty compression ratios.

Secondly, the Yaris is one of the few engines that offers DIRECT INJECTION - which cools the intake charge and as discussed in the following link:

http://www.greencarcongress.com/2009...portfolio.html

10.5:1 is not a high compression ratio for a modern, direct injected, small displacement engine. The 2.4 liter, direct injected GM engine discussed in the link above runs an 11.4:1 CR!

Hence, the 10.5:1 compression ratio in the Yaris engine (where each cylinder represents a mere ~ 0.375 liters and where direct injection is involved) isn't comparable to an engine that utlizes port injection and larger cylinders (particularly the bore dimension).

What amazes me about these bulletin boards is that people voice opinions without having any REAL understanding of the subject matter, most of which boils down to advanced engineering principals.

There is absolutely, positively NO EMPIRICAL EVIDENCE supporting the notion that any modern engine that has a recommended fuel octane rating of 87 PON can, in any way, benefit from a gasoline of a higher octane rating. If anything, empirical evidence suggests the opposite, since the slightly lower burn rate of the higher octane fuel may adversely impact the intended timing of the complete combustion process, relative to the position of the piston and the valves.

What amazes me about bulletin boards is that they somehow produce these attitudes where people assume that other people are oblivious and what they say is the gospel. As cool as you might be, I also have an engineering degree to my credit...and 2 other degrees to boot but that doesn't mean shit. Engine dynamics are pretty involved but fuel is a fairly easy thing to understand. Octane, as you know, refers to a fuel's tendancy to explode rather than burn. A low octane fuel will will burn more violently, releasing it's power/energy sooner than a higher octane fuel while a high octane fuel is more stable, and burns more slowly or energizes at a slower rate. Higher octane fuel can result in a smoother start and idle(more stable and efficient energy). As far as gas mileage goes....there are thousands of opinions and real life proof that higher octane fuels can deliver better mpg's. For example....here is a blurb from good ol' Tony...

http://www.fuelsaving.info/fuels.htm

[darkmoon87]

I love how I started the thread asking about the "smoothness" and the thread turned into a gongshow arguements about MPG and power gains...sigh lol

[CrazedEpidemic]

Originally Posted by ham

I experience a noticeable gain in MPGs from 87 to 93

Thats what happened to me when I went to a Shell station that only had 93. I noticed more MPG.

[DerFlosser]

Originally Posted by darkmoon87

I love how I started the thread asking about the "smoothness" and the thread turned into a gongshow arguements about MPG and power gains...sigh lol

I agree....and the only point that I ever really "tried" to make is that it's definitely possible and not "placebo" that it starts and idles smoother.

[dybbuk]

And 427 seemed to be agreeing with you. However, he also said that smoothness was actually bad for the vehicle. Personally, I don't know much about engines (I am NOT a mechanic), but, I can read. It seems you guys aren't reading each other's arguments. It comes down to that it seems; yes, on higher octane fuels it will run 'smoother', but, it will also generate less power.

[2009Toyotoad]

Originally Posted by supmet

I run 91 every once in a while, and it does feel smoother starting, accelerating, and idling.

Could it be a placebo affect? Maybe
Is it only a 2 dollar placebo, if it is? Yes


With the octane specific argument aside, aren't their cleaners and additives in 91 that aren't found in 87 at some gas stations??

Bingo! We have a winner. Big oil figured out a long time ago that to charge a premium price you need to create a positive preception that the vehicle "just seem to" run smother or more powerful when spending the extra $.10 to $.20 a gallon.

Some oil companies even figured out that they can package the stuff and give it fancy names like "Octane boost, Techron, or fuel system cleaner."

Now there is nothing wrong with buying or using these products. These products do clean the system of carbon crud. However, you can get almost the same effect from running WOT on 50 miles of back country road.

Since some of us don't have 50 miles of WOT roads nearby, these additives are a reasonable substitute.

Just don't fool yourself!

[427chev]

Originally Posted by dybbuk

And 427 seemed to be agreeing with you. However, he also said that smoothness was actually bad for the vehicle.

Show me where I stated that "smoothness is bad for the vehicle."

I NEVER stated that. Please don't put words in my mouth again.

Originally Posted by dybbuk

... It comes down to that it seems; yes, on higher octane fuels it will run 'smoother'...

Please produce third-party empirical evidence to support your claim that higher octane gasoline will cause a modern engine that's designed to run on regular gasoline to "run smoother."

Good luck finding that.

Have you ever heard of the "power of suggestion?" That's what's responsible for any "improvements" that are being claimed in using premium fuel in a Yaris. Objectively and empirically speaking, there are no ACTUAL improvements.

Medicine routinely demonstrates this phenomenon in what's known as "the placebo effect." People "feel better" when they eat a pill that made of compressed flour, for example, as long as the researchers tell the study group that it will make them feel better.

[nerp]

Yeah, it's placebo.

[jkuchta]

The Yaris DOES NOT Have Direct Injection. Direct injection is when the fuel in injected directly into the combustion chamber through an injector (usually a piezo injector) mounted in the roof of the combustion chamber. The Porsche LMP2 car has a direct-injection gasoline turbo engine, while both Audi and Peugeot run direct-injected turbo-diesel engines in LMP1.

The yaris does have indirect port injection (the injector is mounted just behind the intake valves in the intake port)....and in my testing does see gains from higher octane.

When running premium fuel (91 octane here in Cali.) I see more ignition advance than when running regular.

Octane only pertains to a fuel's resistance to detonation, and has nothing to do with flame front speeds, temperature, or the quality of it's burn (i.e. clean or dirty).

The yaris ECU is designed to run a minimum octane of 87 because it has enough range of adjustability to pull timing out to stave of detonation. Running higher octane will allow the ECU to run a more aggresive timing map, making more power.

[07WYarisRS]

yeah we no it will allow it to advance the timing more
BUT why does it advance the timing? What is it that tells the ECU it needs or can go with more timing?

The engine MUST advance the timing more because the 02 sensors are picking up incomplete combustion from too high of octane and a rich air/fuel ratio...
by advancing the timing it creates more heat to help with more efficient combustion...
this is what I have been sayinall along....
the overall power remains the same because the advanced timing is just countering the effects of the overly rich mixture that would be reducing the power output.

Thats why I said if you ran them both in an engine with fixed timing the lower octane will always make more HP, in order for the engine thats running high octane to make the same power you must change the valve timing and ignition timing for more compression/different overlap and earlier spark for a more efficient combustion...
This is why when i'm setting up race engine we start out rich, watch the EGT and CHTs as well as power output. Then start leaning things out. if the CHT's spike but EGTS drop the engine is starting to detonate. if a higher octane is needed we usually have to adjust the timing as well to bring the power back that we lost.

But thanks for proving my point