91 Octane Gas Question

[Bill Marshall]

If I mix 89 octane with 93 octane 50:50, what will I get?

Where I live, all that the gas stations sell are 87, 89, & 93. So, in an effort to save a little money, I was wondering if a mix of 89 & 93 would result in 91, which is all that my fortwo requires. However, I know nothing about the chemistry of gasoline & don't want to create a problem.

Anyone here know enough about gasoline to know if this will work?

Thanks in advance.

[jwight]

Gasoline FAQ

See paragraph 6.15. Not saying this is the final word but it seems to answer your question.

[John_H]

Is the difference between 89 and 93 20 cents a gallon? If the difference is 10 cents, mixing 50% of 89 with 50% of 93 is only a savings of 44 cents in an 8.75g fillup. Is it worth the hassle even at a 20 cent difference?

[Jeff C.]

Dont be afraid to be good to your car.The difference in the lowest octane and the highest octaine is a miniscule amount in the long view.Personally,I ALWAYS go for the 93 octane.As I see it,NOTHING is too good for my car!Live it up----Jeff C.

[John_H]

But what's so good about high octane fuel if it's less combustible and wouldn't result in knocking or timing adjustment anyway? (That's assuming those were the case)

[Bill Marshall]

Originally Posted by jwight

Gasoline FAQ

See paragraph 6.15. Not saying this is the final word but it seems to answer your question.

Thanks for the info, J. Very helpful.

[JediCoda]

In all honesty chaps, you're lucky over there. Having worked and converted our fuel costings into dollars (this also includes the conversion from imperial gallon to metric), here's how the numbers look...
95RON = $8.64 per US gallon
99RON = $9.08 per US gallon <- the stuff I use in my 451, gives little bit better mpg, just enough to be worth it.
Annoyingly, a good 50%, if not more, is tax, duty, then tax on duty

[Old smart]

Originally Posted by jwight

Gasoline FAQ

See paragraph 6.15. Not saying this is the final word but it seems to answer your question.

There is something not said in the reference that could have been. Grossly retarding ingition (e.g. 91 to 87) due to low octane can cause an increase in exhaust gas temperature. The increase in EGT can overheat the exhaust valves and exhaust port side of the aluminum head as well as the catylitic converter, which on a smart is only inches away from the exhaust ports, not feet away as on larger cars.

Also, apparently smart feels like there can be an increase in unburnt fuel getting to the cat due to misfire with sub-octane fuel or other improper operation. smart OpMan:

“! To prevent damage to the catalytic converter, only use premium unleaded gasoline in this vehicle. Any noticeable irregularities in engine operation should be repaired promptly. Otherwise, excessive unburned fuel may reach the catalytic converter, causing it to overheat and potentially start a fire.”

[Brabus]

Originally Posted by JediCoda

In all honesty chaps, you're lucky over there. Having worked and converted our fuel costings into dollars (this also includes the conversion from imperial gallon to metric), here's how the numbers look...
95RON = $8.64 per US gallon
99RON = $9.08 per US gallon <- the stuff I use in my 451, gives little bit better mpg, just enough to be worth it.
Annoyingly, a good 50%, if not more, is tax, duty, then tax on duty

LOL, that reminds me when I was in Portugal in March. I rented a microhybrid Smart. I was on their autobahn and I stopped to get gas. I was short on cash so I went inside to prepay with a mere 20 Euros and I told them I wanted regular gas. He insisted the car was diesel and I said no, it's gas, so long story short he got really frustrated with me because we couldn't understand each others language. And he waved me out of the store to go fill up. So I go out and learned that you can't put regular unleaded gas into a premium gas car. They have different nozzle sizes for different grades of petro, so you can't put the cheap stuff if the car requires premium gas whereas in the states you have the option to put whatever grade you want. So he was trying to tell me that I couldn't get regular gas that I needed either premium gas or diesel, and I knew it took premium but I was out of money and far from where I was staying. I found it funny because he was so annoyed with this stupid American wanting to put low grade into the Smart. What happened was I didn't know the autobahn cost 18.60 Euros one way (37.20 EUROS both ways...and they don't have cards they give you with the prices either like you get in Jersey, rather you find out at the toll how much you owe. I gave her 5 Euros thinking it was inexpensive since the GWB-like bridge was only 1.25 euros and she looked at me with a strange glare and pointed to the digital readout, lol) so I spent like 120 Euros on a trip that was about 5 hours roundtrip just in gas and tolls. Also didn't know it was even an autobahn, so I ended up staying in the far left lane going about 80+mph and at those speeds in a Smart it was literally getting about 20mpg especially with the winds. Horrible trip. And of course there were a zillion cars going 120+mph burning all kinds of gas at those speeds so I guess people still drive fast and guzzle gas even at expensive gas prices. Yet that's one reason Europe has so many small cars over there...driving is EXPENSIVE in Europe especially on that autobahn. You really need a faster car to be on it although there were some other cars going about the same speed.

I always put the higher octane in the Smart except when I'm stuck on Portugal's autobahn paying ridiculous tolls (although the bigger nozzle made me put in the higher octane anyways), funny thing is the huge bridge there in Lisbon is cheap to cross, but the autobahn makings the NJ Turnpike look like a bargain.

If you followed Paragraph 6.15, then you'd be filling up at every half a tank, every 4 gallons saving a quarter!

[Big Panda]

I look at it that way as well.....difference between 87 octane (reg) and 93 octane (premium) is 'only' .20/gal here in Central Indiana.

Like someone said, I'm only saving about $1.75 per fill-up so it's really not worth it to me. $5.00? Yes, but I'm not sweating over saving less than $2.00, regardless of the price of gas per gallon.