The last gas question

[newyar]

Originally Posted by Ace

This is what I’m sick of. People assuming things that they have nothing to back it up with. I never say that higher octane is better for the yaris engine, just show me some proof that is not if you're going to make that claim. I did show where some would say it is better but did not state my opinion. If you’re going state your opinion then show me some facts.

I spent half my life working in the labs and offices of the world largest gasoline and oil companies here in Houston, would love to read some facts and not opinions.

Well if you worked half your life in the labs and offices of the gas and oil companies as you claim then you wouldn't be asking for facts; you'd already know. How about you just contact Toyota, you know the people who DESIGNED THE ENGINE and ask them what they meant when they PUT IT IN THE MANUAL? Since you don't seem willing to accept the owner's manual as "facts" it won't matter what I or anyone else on this forum says.

Oh and keep in mind that the gas and oil companies WANT you spending more money on the higher octane fuels so they aren't about to tell you otherwise. Ask people who rebuild engines for a living; who service fuel and ignition systems; who make spark plugs, valves, rings, pistons. Ask the people who deal with the consequences of tens of thousands of miles of fuel usage in engines; they'll give you some "facts".

If you're "sick and tired" then relieve your symptoms by doing some research yourself instead of demanding others do it for you. I stated what I know based on decades of experience with cars. If you don't like it or disagree with it; fine. Everybody is entitled to their opinion. Why don't you just fill your tank with 87; run it out, measure your gas mileage. Then fill up with 92 and see if you can tell any difference other than the cost. If you can't, then there's your "facts". But it's your car; spend your money on whatever grade fuel you want to.

[Ace]

Originally Posted by newyar

doing some research yourself... Everybody is entitled to their opinion.

Thank you for admitting that you have no proof and it’s just an opinion.

[keesue]

The Yaris was desgined to run on regular. Toyota states 87 octane as the minimun recommended fuel (nothing lower) in the owner's manual. Save the money for beverages and a turbo charger.

Toyota designed the car with computer controls to enable it to run a relatively high compression on 87 octane by dynamically retarding ignition timing based on feedback from the knock sensor; further, they designed variable valve timing to scavenge exhaust from the cylinders more efficiently at higher rpm, lowering cylinder temperatures for the incoming charge. Without this technology, the engine would require higher octane fuel to avoid fuel detonation. Temperature, the by-product of compression, is the determinate factor for octane. The higher the compression, the higher the temperature and the higher the octane requirement. By old school standards, the Yaris is a very sophisiticated little engine.

The Yaris' timing does not advance to account for higher octane fuel. Without higher compression, it would be pointless. It only retards from its set point to account for higher temperatures from engine load that would result in knock. The set point can be adjusted if this is out of spec or objectionable, but a little pinging under load especially in high ambient temperature is normal and is a sign that the engine is squeaking the last bit of energy out of the charge.

Unfortunately, the Yaris doesn't dynamically raise its compression ratio without the assistance of forced induction. Using a higher grade fuel isn't required. Without higher compression, higher octance fuel in and of itself, won't improve the Yaris' peformance or extend its mpg to justify the expense; but, if you want to spend the cash....