Premium Gas

[hystria]

Originally Posted by cleong

So we should only run the absolute minimum RON recommended and anything above is just a waste of money?

PROBABLY higher octane/RON will provide better fuel economy with this car... but the difference will be too minimal to be easily measured by just checking a mileage variation. YES, Toyota recommends using higher octane/RON for this engine in order to obtain better mixture burning, resulting in less polluting emanations. Buying 10-15% more expensive 89/91/94 gasoline won't result in 10-15% mileage increasing. Check out the black smut (?) on the exhaust when running on 87 octane, then whip it off and switch to 91 and check again.

[fu_im_from_texas]

Originally Posted by hystria

PROBABLY higher octane/RON will provide better fuel economy with this car... but the difference will be too minimal to be easily measured by just checking a mileage variation. YES, Toyota recommends using higher octane/RON for this engine in order to obtain better mixture burning, resulting in less polluting emanations. Buying 10-15% more expensive 89/91/94 gasoline won't result in 10-15% mileage increasing. Check out the black smut (?) on the exhaust when running on 87 octane, then whip it off and switch to 91 and check again.

"....using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual."
http://www.ftc.gov/bcp/conline/pubs/autos/octane.shtm

why do people insist on ignoring empirical and statistical data?

[bearda]

This is one of those discussions that just doesn't go away. I've seen the same thing on almost every non-premium fuel car forum I've seen. The signal to noise ratio tends to vary, but you've always got a couple people clinging to numbers and reports, a couple people clinging to their anecdotal evidence, and a couple people clinging to some hope that they can improve performance.

Just to add fuel to the fire, though, I don't think higher octane gas is going to do much of anything for you (nothing good, at least). Higher octane gas doesn't give you higher performance; it just resists pre-detonation. If you're at the point where the ECU is retarding timing due to pinging it'll keep you from losing performance. Unless the ECU is really designed for performance it isn't going to keep advancing the timing on it's own unless it's already retarded the timing (There are some that do do this. The WRX actually starts with a very conservative timing advance then ramps it up until it knocks, then pulls it back a little).

Higher octane gas CAN give you better mileage if the car can take advantage of it. Octane rating is basically a measurement of how long it takes fuel to burn. If the fuel burns longer you don't need to burn quite as much of it in the optimal case. You've got to get the ECU to realize that, though. If the ECU keeps the same ignition timing/AFR/whatever you're not going to see any benefit.

One thing I have seen with higher-octane fuel on a car factory-tuned for 87 is starting delay. From what I can tell (and this is coming almost entirely out of my ass, as this goes right past my league) since higher octane gas is more resistant to predetonation sometimes it's also a little too resistant to initial detonation. You try to start the car and the ECU finds the gas a little harder to light than it thought. Not a big deal at all, but at times an indicator that lower octane gas can actually run better than high-octane.

If you're looking for the best gas for your car just buy GOOD gas, not higher-octane gas. Go with a station that stocks gas with additives and detergents in it's 87. Chevron is a great example of this; they put their Techron additive in all the gas they sell. Once again, it's isn't going to add any more performance or gas mileage the car didn't have at one point. Maybe it'll keep it running a little cleaner, though, and it's my personal opinion that you're more likely to see a benefit from that than running high-octane gas.

[hystria]

Originally Posted by fu_im_from_texas

"....using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit.

TRUE. As per Yaris manual, it recommends 87 or higher. Why "or higher" ? Ever wonder why Toyota recommends wasting your money ? With NO REASON ? Is Toyota in business with Shell ? Well, if not, there should be a reason, unless there are places on Earth that sell only 89 or higher octane gasoline... don't think so...

Engines are optimized to run with a precise level of octane. If an engine requires 87 and the owner put 89 or higher, there will be absolutely no benefit for the engine. On the other hand, if and engine is optimized to run with 89 and the owner uses 87, the engine will not run at 100% performance. It will knock more or little because the mixture ignites before the optimum moment during compression, thus leading to hot points on the piston/ring surface. Because the mixture ignites before the moment when the engine compression is optimal, it produces less overall performance. But not by much, one will not be able to feel any difference.

To resume... if using 87 the engine starts knocking, try changing the brand... the Yaris engine should not be knocking to an audible/damageable level while using good quality 87 octane gasoline.

[Pavel Olavich]

Originally Posted by hystria

TRUE. As per Yaris manual, it recommends 87 or higher. Why "or higher" ? Ever wonder why Toyota recommends wasting your money ? With NO REASON ? Is Toyota in business with Shell ? Well, if not, there should be a reason, unless there are places on Earth that sell only 89 or higher octane gasoline... don't think so...

Engines are optimized to run with a precise level of octane. If an engine requires 87 and the owner put 89 or higher, there will be absolutely no benefit for the engine. On the other hand, if and engine is optimized to run with 89 and the owner uses 87, the engine will not run at 100% performance. It will knock more or little because the mixture ignites before the optimum moment during compression, thus leading to hot points on the piston/ring surface. Because the mixture ignites before the moment when the engine compression is optimal, it produces less overall performance. But not by much, one will not be able to feel any difference.

To resume... if using 87 the engine starts knocking, try changing the brand... the Yaris engine should not be knocking to an audible/damageable level while using good quality 87 octane gasoline.

The "or higher" phrase only means that if 87 is not available, then using a higher octane is not going to damage your engine.

Don't be so quick to read more into the words, then what is literally meant.

Also, to suggest as a remedy, to use higher octane than called for in the manual, a way to remove knocking is plain wrong. It would be far better to take the car in and determine why it is knocking at the required octane, and to remedy the problem. Going up in octane is a band-aide that only masks a real problem.