Will 91 octane make a car get better gas mileage?

[Quickstep192]

My recent model Honda gets decent gas mileage, but it holds so little gas, it still seems too short between fill-ups. A little performance boost wouldn't hurt either.

I've heard that using 91 octane in a car designed for 87 octane will do nothing; I've also heard that the ECU in modern cars will figure out that you're using higher octane gas and adapt providing better gas mileage and performance.

Does anyone know conclusively?

[WolfeMacleod]

no

[speeder]

This has been covered extensively here in the past but using the correct octane recommended for the vehicle will get the best efficiency, which means power and mpg. Using 87 in a high-compression engine that requires premium will cause poor performance, sometimes in a severe way. Using higher octane fuel in an engine designed for 87 will not only not give you any benefit, it may actually reduce efficiency slightly. The reason for this is that higher octane fuel is LESS EXPLOSIVE than low octane fuel.

The short answer is no, you will not get any benefit from using the wrong fuel. It helps to really learn what octane is and you will never have to ask again.

[Scott Douglas]

What model Honda do you have?

Have you read your owner's manual?

[Bob Kontak]

Originally Posted by speeder

Using 87 in a high-compression engine that requires premium will cause poor performance, sometimes in a severe way.

Drove my brother's Volt from Charlotte to Akron. Did not know that premium is required for the one point something liter gas engine part of the system.

Got into a situation where it was uphill and and a truck was pinching me off. I was dead in the water. Hit the shoulder for safety.

[GH85Carrera]

No.

Lower octane at most will cause a slight decrease in maximum HP. Under normal driving conditions you will notice little if any change.

[Bob Kontak]

Originally Posted by WolfeMacleod

no

Agree. Nothing.

[RANDY P]

I did a 4 hour trip once using 87 one way and 91 coming home- vehicle was a 2002 chevy s10 v6. Absolutely no difference in mileage, literally.

Octane is like shoe size- get what fits. Manual calls for 91, use it.

[Scott Douglas]

How many of you guys posting here actually own a Honda?

[Scott Douglas]

It'd probably surprise you if I told you the Honda ECU's can adapt to higher octane use. After prolonged use the anti-knock sensors allow the mapping to change where ignition advance can take advantage of it.

[Bob Kontak]

Originally Posted by Scott Douglas

How many of you guys posting here actually own a Honda?

I had a 96 Odyssey.

Why you asking?

[motion]

I've always been told that lower octane fuel creates the most HP in my low-displacement race bikes (carb'd).

[Bob Kontak]

Originally Posted by Scott Douglas

It'd probably surprise you if I told you the Honda ECU's can adapt to higher octane use. After prolonged use the anti-knock sensors allow the mapping to change where ignition advance can take advantage of it.

That's cool. What year is OP's Honda?

[Scott Douglas]

No offense, but that's like saying I had a 386 computer.
Things have changed a lot since '96, especially with Honda engine management systems.

[KFC911]

Octane will not efffect mpg, but if you can find ethanol free 87 octane, you will improve it....enough to offset the price difference at the pump mebbe...YMMV...truly.

[Scott Douglas]

Guess we'll just have to wait for the OP to come back and tell us what year car he has.

[Bob Kontak]

Originally Posted by Scott Douglas

No offense, but that's like saying I had a 386 computer.
Things have changed a lot since '96, especially with Honda engine management systems.

I remember when the 286 came out. Three puffs on a cig and the calcs were done.

It was heaven.

[stevej37]

I drive two Hondas. My Prelude has stickers on the dash and the gas fill door saying 'use prem fuel only'....which I do.
My Honda Fit calls for reg gas, but I always use prem in that one also. I put a custom intake and exhaust on it and the prem fuel seems to give it more pep.
The Fit gets consistently 40 mpg with either gas type.

[Scott Douglas]

I can remember upgrading my 286 to a 386 and thinking NOW I'm cookin' with gas.

[Scott Douglas]

Originally Posted by motion

I've always been told that lower octane fuel creates the most HP in my low-displacement race bikes (carb'd).

I'd guess that's because your bikes would be unrideable with the ignition advance that would be needed to take advantage of the higher octane if used.