Octane: 87 v. 91

[2XOverhead]

I tell ya, it makes a difference. Put in regular for the first time the last couple of fill-ups outta pure curiosity. The truck just ran rougher, acceleration not as steady and smooth, engine purred much less. Switched back to premium, everything back to normal.

EDIT: Mods, I meant to put this thread in the Engine and Drivetrain section. Feel free to delete.

[rx7vert]

Originally Posted by rich29_cal

I tell ya, it makes a difference. Put in regular for the first time the last couple of fill-ups outta pure curiosity. The truck just ran rougher, acceleration not as steady and smooth, engine purred much less. Switched back to premium, everything back to normal.

EDIT: Mods, I meant to put this thread in the Engine and Drivetrain section. Feel free to delete.

That only happens because your computer has learned to adjust for premium fuel. If you had been running regular since new, it wouldn't spit or sputter at all. In an engine that is designed to run on regular 87, higher octane fuels are actually worse. Higher octane fuel burns for longer, and is still burning as the exhaust valve opens. Regular fuel is faster burning and is generally through with the hottest part of it's burn before the valve opens.

It is a difference that you will probably never see or have any ill effects from, unless you start running 110 octane race fuel.

[Leland]

Originally Posted by rx7vert

That only happens because your computer has learned to adjust for premium fuel. If you had been running regular since new, it wouldn't spit or sputter at all. In an engine that is designed to run on regular 87, higher octane fuels are actually worse. Higher octane fuel burns for longer, and is still burning as the exhaust valve opens. Regular fuel is faster burning and is generally through with the hottest part of it's burn before the valve opens.

It is a difference that you will probably never see or have any ill effects from, unless you start running 110 octane race fuel.

I doubt a Tundra will optimize up to 110 octane. Maybe, but I'd be surprised.

The burning depends on the mixture and valve timing. If the timing is optimized, with higher octane, you can use more air, which will result in better burning efficiency.

Most normal cars are designed for regular and therefore won't benefit nearly enough to justify premium. While most will run on regular, cars designed to run on premium will notice a significant performance drop on regular fuel.

There is another point. As engines age, they pick up deposits that can negatively affect the spread of the flame front from the spark plug which can also lead to detonation. Premium fuel will help to prevent this.

[HOGWILD]

I was told that premium fuel did not completly detinate and would burn worse at our altitudes 5300 Ft causing more buildup? That is why they only have 86 octane in NM for regular unleaded! My truck has never pinged using it since new!

[rx7vert]

Originally Posted by Leland

I doubt a Tundra will optimize up to 110 octane. Maybe, but I'd be surprised.

The burning depends on the mixture and valve timing. If the timing is optimized, with higher octane, you can use more air, which will result in better burning efficiency.

Most normal cars are designed for regular and therefore won't benefit nearly enough to justify premium. While most will run on regular, cars designed to run on premium will notice a significant performance drop on regular fuel.

There is another point. As engines age, they pick up deposits that can negatively affect the spread of the flame front from the spark plug which can also lead to detonation. Premium fuel will help to prevent this.

Mixture and valve timing, yes, but also compression. Higher compression means more heat in the chamber and a faster burn. Our tundras don't have compression high enough to need the slower burning fuel.