Just filled up the tank with 91 octane premium fuel

[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

[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.

[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

[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

[2009Toyotoad]

Originally Posted by 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

This is probably a question best answered by a local Toyota dealer. They should have the best knowledge on local conditions and fuel qualities.

[borezack]

There is no local Toyota dealer here. The closest one is over 130 miles away.
Will 85 octane damage the engine?

[mryaris]

Originally Posted by borezack

Will 85 octane damage the engine?

No. 85 octane is used in locations with high altitudes because it behaves like 87 does at lower altitudes/sea level. I live in Colorado and regular is 85, mid is 87 and premium is 91.

So.....to clarify a bit, high altitude 85 octane= the 87 octane that all the low-landers use, so using mid-grade 87 is not necessary.

[Flipper_1938]

Originally Posted by 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

Probably had more to do with the denser air than the fuel...

[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.

[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

[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.

[ChinoCharles]

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

[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.)

[Nudger]

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