Premium vs regular fuels

[fumanchu1]

Originally Posted by Hotrodheart

@Tcoat does sugar free maple syrup have less octane than the regular kind?

Sugar free maple syrup?!? that's like saying gum free gum!!!

[Capt Spaulding]

Or non-alcoholic gin. What's the point?

[Tcoat]

Originally Posted by fumanchu1

Sugar free maple syrup?!? that's like saying gum free gum!!!

sugar free sugar!

[joe strummer]

Originally Posted by VTEC

The FR-S and BRZ were tuned by factory to use 93 octane under North American rating.

Anytime you use something below factory settings, the computer will detect that because the fuel will start to detonate when it's not supposed to. The computer will detect the explosions and compensate by lowering the compression and horsepower to prevent more premature detonations.

The reason why family cars get no benefit from premium fuel is because they are usually tuned to 87 octane. And if you decide to put 91 octane in your Corolla, there is no way for the Corolla's ECU to detect that. And you would be wasting your money again.

Actually, our cars are not "tuned" for 93 octane, or any other octane. Octane requirements are dependent on the engine's compression. Octane in effect raises the temperature at which the fuel mixture will ignite.

We need fuel with a higher octane because our engines are high compression. Higher compression=higher temperature.

Also, the engine's computers don't lower compression when knock sensors detect knock. How could they? Compression is fixed. The ECU changes the engine timing to compensate, based on signals from knock sensors. You'll get less horsepower, but that's just a by-product of the less-than-optimum timing.

Lastly, it doesn't matter if the ECU could detect what octane fuel is put in the tank. What would it do with the information?

[Packofcrows]

Originally Posted by joe strummer

Also, the engine's computers don't lower compression when knock sensors detect knock. How could they? The ECU changes the engine timing to compensate, based on signals from knock sensors.

Indeed!

I notice this when using super cheap $2.60 91 Oct vs Chevron $3.09 or Shell 91 Oct $3.15.

I spoke with Gas Station owner and he said it's due to the ethanol and lack of additives. I noticed the spark plugs wearing out quicker with 87 oct on friends IS300 when manual said to us 91. Gas station owner said ethanol content was about 20-26% (?).

I always thought ethanol tops in gas was about 10%???

[billwot]

Originally Posted by joe strummer

Actually, our cars are not "tuned" for 93 octane, or any other octane. Octane requirements are dependent on the engine's compression. Octane in effect raises the temperature at which the fuel mixture will ignite.

We need fuel with a higher octane because our engines are high compression. Higher compression=higher temperature.

Also, the engine's computers don't lower compression when knock sensors detect knock. How could they? Compression is fixed. The ECU changes the engine timing to compensate, based on signals from knock sensors. You'll get less horsepower, but that's just a by-product of the less-than-optimum timing.

Lastly, it doesn't matter if the ECU could detect what octane fuel is put in the tank. What would it do with the information?

[mdm]

And high compression ratiio helps achieving better thermal efficiency of the engine.

[ame="https://www.youtube.com/watch?v=t4yh5Pt8was"]Compression Ratio and Thermal Efficiency - YouTube[/ame]

In other words, the high CR and the need for high octane are some of the costs of squeezing 200 HP form 2 liters.

[VTEC]

Originally Posted by joe strummer

Actually, our cars are not "tuned" for 93 octane, or any other octane. Octane requirements are dependent on the engine's compression. Octane in effect raises the temperature at which the fuel mixture will ignite.

We need fuel with a higher octane because our engines are high compression. Higher compression=higher temperature.

Also, the engine's computers don't lower compression when knock sensors detect knock. How could they? Compression is fixed. The ECU changes the engine timing to compensate, based on signals from knock sensors. You'll get less horsepower, but that's just a by-product of the less-than-optimum timing.

Lastly, it doesn't matter if the ECU could detect what octane fuel is put in the tank. What would it do with the information?

You're right it reduces timing, not compression, my bad, and that in effect reduces the horsepower.

But what I mean is your ECU can detect fuel octane below factory specifications (or factory "tune") and compensate by reducing timing/power. But putting higher octane than factory specs, will not have the opposite effect. The ECU will not detect higher octane or do anything to take advantage of it.

[joe strummer]

The ECU doesn't detect octane. It gets a signal from the knock sensor and retards timing. There are a number of causes of knocking. Low octane is one of them.

[billwot]

Originally Posted by joe strummer

The ECU doesn't detect octane. It gets a signal from the knock sensor and retards timing. There are a number of causes of knocking. Low octane is one of them.

[Luftwaffel]

I had to retard my brain timing to read this thread.

Fuel quality is easy to measure. You guys are overthinking shit. It's called a data log.

For the Californians... mixing 91 and 100 is silly. You literally have E85 stations everywhere. Get a flex fuel kit.

[stevesnj]

I think fuel issues should be a sticky and anyone making a new thread should be deleted IMHO. I'd say this goes for oil and tire threads. :P Happy Bunny Day!

[Zhangy]

Originally Posted by Tcoat

Manual says: Recommended 93 Required minimum 91. All is good in the world.

all engines must be designed to run on 87 octane, 2L boxer engine is no different. using 87 octane will do no harm, because it's the rule. The manual says a lot of things to lower the liability of the manufacturer such as touchless wash only, wash after driven on salty road every time, don't mod your car... you get the point

[Legionsk88]

Originally Posted by Luftwaffel

I had to retard my brain timing to read this thread.

Fuel quality is easy to measure. You guys are overthinking shit. It's called a data log.

For the Californians... mixing 91 and 100 is silly. You literally have E85 stations everywhere. Get a flex fuel kit.

i will have to disagree with you on the E85 stations being everywhere, the nearest one from me is a good 20 miles from me, so a 40 mile trip for it, would not be very economical for me.