Just filled up the tank with 91 octane premium fuel

[PHXDEMON]

I run 91 octane and add 2 bottles of chevron octane booster into each tank. Needless to say I run 13's at the track

[ChinoCharles]

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

Never been on a car forum before?

Save yourself the money and run GOOD 87. If you want to do your engine a favor, BUY GOOD GAS. People will go to Korner-Mart and buy 93 and say "hey, look at me... I'm concious." You're not. Just buy good, basic gas... 87 from Shell, Sunoco, etc. Its a Yaris people... not a Bimmer.

[jkuchta]

Originally Posted by 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

That's an interesting idea...but a little out in left field..the ECU is programed to run the most advanced timing it can get away with without detonating...that's why the timing is more advanced with the higher octane.
The reason you would want to run the timing as advanced as possible is that it will lead to higher cylinder pressures, which equal more torque.

The octane rating of the fuel has no bearing on the mixture setting, other than the fact that with a more knock-resistant fuel you may be able to run a little leaner without problems.

[07WYarisRS]

Originally Posted by jkuchta

That's an interesting idea...but a little out in left field..the ECU is programed to run the most advanced timing it can get away with without detonating...that's why the timing is more advanced with the higher octane.
The reason you would want to run the timing as advanced as possible is that it will lead to higher cylinder pressures, which equal more torque.

The octane rating of the fuel has no bearing on the mixture setting, other than the fact that with a more knock-resistant fuel you may be able to run a little leaner without problems.

the ECU pays more attention to ther F/A ratio to control the engines timing then the KNOCK sensor... you get better mileage and long engine life by controling the engine fuel/air temps and engine temps then controling just knock...besides your not going to get knock at 1/4 throttle or slow cruise speeds or low rpm operation.

So let me get this strait if I add an octane booster the bumps it up 4 points 87.4 octane because of the additives that reduce knock to as much as a 91 octane it will max out the timing to the highest possible timing and the cheapest octane booster on the market will magically give me more HP because the ECU only listens to the knock sensor for when to alter the timing...
Well my racers use 100+ octane in thier race bikes so I guess i better start running that because then I will make the most HP out of all ya'll
yeah i don't thing so.

[07WYarisRS]

http://www.youtube.com/watch?v=2jbcC...eature=related

here is the perfect example, higher octane when not needed actually reduces HP
I'll never argue the FACTS when talking about increased compression and forced indiction, i have built many engine N/A and boosted.
Sure these cars can and WILL see power gains when using higher octane levels that will allow an engine to run at higher boost levels without knock. BUT these cars were designed to run higher octane fuels, but made to accept low octane as well.

but we are talking about a stock Yaris here and economy car designed to run on economy fuels for the best bang per buck per mikle and the quesion is if the higher octane gives any mileage or performance gains over 87
87 will give you the best MPG in this econo box

[ChinoCharles]

^^ Use 87 or 07WYarisRS will find you while you're sleeping and cut your brake lines.

[jkuchta]

Originally Posted by 07WYarisRS

http://www.youtube.com/watch?v=2jbcC...eature=related

here is the perfect example, higher octane when not needed actually reduces HP
I'll never argue the FACTS when talking about increased compression and forced indiction, i have built many engine N/A and boosted.
Sure these cars can and WILL see power gains when using higher octane levels that will allow an engine to run at higher boost levels without knock. BUT these cars were designed to run higher octane fuels, but made to accept low octane as well.

but we are talking about a stock Yaris here and economy car designed to run on economy fuels for the best bang per buck per mikle and the quesion is if the higher octane gives any mileage or performance gains over 87
87 will give you the best MPG in this econo box

I didn't see anywhere in that video where they played with the ignition timing to take advantage of the higher octane.

PLUS...

this thread is about higher octane fuel, not additives.

[TheSilkySmooth]

Originally Posted by 07WYarisRS

our engines are NOT high compression... my street bikes run 200psi plug per cylinder and run on 87 octane... guess what they have less then 10:1 compression ration.

The ECU will not re-tune for higher octane...
The only time it will make a difference is if the engine is knocking... then the knock sesor will pick up the engine knock and retard the timing.. it won't change the fuel maps to compensate.

Spark knock AKA PING is completely normal and just means the engine is running efficiently...

running a lower octane fuel will reduce carbon built up as it has a lower flash point and will burn more efficiently and completely... Also start running a TRUE synthetic like Amsoil or Redline with no mineral oil or by products that cause deposits to form and after 10 years you engine will still be 95% carbon free

So 10:1 in the Yaris is NOT high compression? BAH! 2) The ECU is CONSTANTLY adjusting the fuel trim for proper running as required!
3) How do you know if the timing is in retard (without a scan guage) on WOT?

All that said, I usually run regular. If the engine is healthy, and NOT carboned up, it should run OK on 87PON. I think I cooked my cat#1 from driving too hard and have to get it replaced with the high flow ( for free!?) on the TSB EGO35-06 .... Car is feeling lazy and getting choking sulphur smell in the cabin when I whomp on it

[07WYarisRS]

No 10:1 is not high compression, not nearly enough for high octane fuel...

I know this thread is about high octane fuel but whats the differenece between 87 and 91 octane? really? Additives or lack of that neutralize or remove free radicals in the fuel the promote detonation.
There is no difference performance wise between a h91 octane fuel and an 87 octane with a 7 point octane booster added, Both will resist knock the same amount.
Thats all there is to higher octane fuel...nothing more. Its resistance to uncontroled combustion... there is no HP gains to be had unless your engine is running forced indiction or compression to high for 87 octane... the YARIS does not have too high of compression for 87

I know the ECU is constantly working to control "proper running" that why it has oxygen sensors and a field of others.
Some want us to belive that the ECU listens to the knock sensors to control the timing.
Others like myself belive that the ECU use incommming air temps and volume, F/A ratio, VVT & rpm and TPS to control the engines power/fuel delivery and timing for the most optimal combustion. Add in all these factors and you won't see any performance gains from higher octane fuel

[TheSilkySmooth]

We are lucky since the yaris has advanced yamaha designed cyl heads, and small bore/long stroke (undersquare) which would reduce the chance of detonation. But cars with large dia pistons like a subaru 2.5L would be more prone to knocking - so they employ intake tumble generators and EGR to get the autoignition temp down. But in an absolute sense 10:1 is high compression. In my book I make the cut at 9:1 high to low. If you rate 3 categories: high middle and low for RACE, I would say 10:1 is middle for Gasoline. Then you have distinctions for alky and Diesel which is a whole nother enchilada ...

[TheSilkySmooth]

I'm sick of people saying the yaris is "only 100 HP" This is a VERY high state of tune for a street motor under warranty. Not as high as an old VTEC Integra/Civic, but if it was a 5.0 mustang in the same tune, it works out to 350 HP! (calc: 5.0L is 3.33 times the size of 1.5L yaris X 105hp.)

[ROCKLAND TOYOTA]

Originally Posted by TheSilkySmooth

I think I cooked my cat#1 from driving too hard and have to get it replaced with the high flow ( for free!?) on the TSB EGO35-06 .... Car is feeling lazy and getting choking sulphur smell in the cabin when I whomp on it

WRONG, your cat was doomed from the start. HENCE the TSB from way back in the begining of 2008....

[TheSilkySmooth]

Originally Posted by ROCKLAND TOYOTA

WRONG, your cat was doomed from the start. HENCE the TSB from way back in the begining of 2008....

Whadya mean - its doomed to fail and just a matter of time b4 it clogged? RockToy - Does the TSB concern the #2 cat further back, or, the #1, Or the pipe in between? Sorry for all the Q's. You think they will give me a hassle(the old melted grocery bag story) ? or is there a back pressure test that it would show up on? Thanks for the help man

[Nudger]

89 and 91 octane wow!! thats so low. I usually use 95 put perfer to use 98 with 10% ethnol

[Yaris Hilton]

You're looking at Research Octane Number. It's established in a special low speed engine with cold air intake and a low operating temperature. There's also a Motor Octane Number that's much more reflective of fuel performance in real world automotive engines, but it's a considerably lower number. When the US required posting of octane numbers at the pump, the various involved parties couldn't agree on which number to post, so they compromised on the average of the two, R+M/2. It's actually a meaningless number as the "sensitivity" or difference between the two numbers can vary substantially, so one "87 pump octane" gasoline may knock more easily than another.

[liyux2k]

the engine is already running at max specs with 87. what ever better fuel you put in just going to force the engine to wear more in order to burn it since the compression stays the same. is not going to boost performance or mileage, the only thing it does is more wear towards the engine. ;)

[SilverGlow]

Only idiots put high octane gas in a itty bitty Yaris motor...they say they "feel" the difference...all BS....higher octane means higher flashpoint, meaning LESS POWER, LESS TORQUE, LESS MPG...LESS CLEAN COMBUSTION....

Leave the 91 octane to motors truly need it like high compression engines, turbo engines, super charged, many BIG displacement engines, etc....only boy racers with one foot still in the sand box swear by 91 octane....all that money wasted...it adds up after years of stupidity....

[borezack]

Hello first post here.

I have an 08 sedan.

Just would like to know if I should change from using 85 to 87.

I'm driving at 3000 to 10000 ft elevation and regular here is 85, plus is 87 and premium 91.

Also Just took a trip and was about 200ft above sea level and I used 87 since that was regular and my car felt like a rocket ship lol

Just would like some input.

Thanks