Just filled up the tank with 91 octane premium fuel

[DerFlosser]

higher octane fuel is a cleaner ignition assuming you have a healthy ignition system (all components). Other than than...one would really be hard pressed to tell the difference between an 89 and a 91 in a Yaris. It's a low-mid compression motor with 100hp. I can possibly see smoother starts but as far as running and gas mileage....we all know that the higher octane provides no benefits.

[07WYarisRS]

Originally Posted by DerFlosser

higher octane fuel is a cleaner ignition assuming you have a healthy ignition system (all components). Other than than...one would really be hard pressed to tell the difference between an 89 and a 91 in a Yaris. It's a low-mid compression motor with 100hp. I can possibly see smoother starts but as far as running and gas mileage....we all know that the higher octane provides no benefits.

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

[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.

[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