How do you like using so-called bio-gasoline and bio-diesel fuel which is often referred to as "corn gas"?

@JackDaniels
Do you drive a Flex-fuel vehicle?

@swirlie my last one was flex, current one no.

@JackDaniels
You don't use E85 in your current vehicle I hope... 🫣

@swirlie no, not compatible with my current truck. Just 91 octane

@JackDaniels
I do nautical marine tech research as a marine Journalist, then translate the information from tech manuals into layman's terms, assisted for accuracy by a licensed marine engineer who explains to me what widgets really are.

So this issue of octane came up and many women boat owners have asked me the same question, which I ended up doing some research on... why use 91 octane or higher? Why do you use it, Jack?

@swirlie I think my truck just runs better on the higher octane.

@JackDaniels But if the engine isn't tuned to use the higher octane, it just blows out the exhaust. At least that's always been my understanding. What does your engineer say, @swirlie??

@sarabee1995 it has a tune on the engine and requires it.

@JackDaniels
Oh, for sure it will run better, but running low octane 87 will not hurt the engine or void the warranty I discovered, even on high-end cars like Porsche or Mercedes which specifically require 91 or higher.

What I discovered from tech reference manuals in the auto industry, was that your truck for example, is advertised by it's manufacturer to have lets say... 300 horse power. When they make that assertion, they are actually guaranteeing that amount of horsepower on a new engine after any break-in period.

What that 300 horse power is based on is the use of a very specific octane rating of fuel. The more octane they use in the test, the higher the rated horse power will result on the test meter.

If they are trying to sell a truck that's based on lots of horse power, they will use high octane fuel during the static tests, which then yields a maximum result, which is then published in owner's manuals as being gospel.

The thing is, if you want or NEED that same horse power, then you'll have to use the octane rating that was used during the manufacturer's test results, like 91 for example or 94 for cars like a Corvette.

But if you don't need the power, you can actually use 87 octane if you're prepared to sacrifice power for economy. That's why it says on the gas filler cap to use 91 octane, because THAT was the octane rating that was used to establish the published numbers for legality purposes!

@swirlie I understand the octane rating and if my truck was not tuned, I would run 87 octane.

@sarabee1995
All vehicles, be they cars, trucks or marine engines, have what's known as "auto tune", which means the onboard computer automatically adjusts the engine's timing to compensate for whatever octane grade of fuel is used, including higher percentiles of ethylene mixed with the gas (ethylene is corn-based alcohol).

There is no such thing anymore as an engine being 'tuned' to use a specific kind of gas. Years ago, getting a tune-up in a car achieved this objective, but tune-ups are no longer required on any vehicle because of this 'auto tune' feature that is controlled by the vehicle's computer.

@swirlie Very interesting. Thanks!

@JackDaniels

Your truck automatically adjusts it's 'tune' or timing to accommodate varying percentages of octane or lack thereof, which is why you can safely use 87 if you're prepared to compromise on the power output of the engine.

@sarabee1995
You're very welcome. If the Dealer recommends that you bring the Subaru in for a tune-up, just say thanks and run!