Recommended Octane Level

[Tango]

My Fiat shop manual recommends octane level of "at least 91". It doesnt differentiate between model years or FI /Carb. I have a 1981 FI Spider.

I bought gas for it for the first time three days ago. I have no idea how long the old gas was in the tank, it could easily have been from last year -- the previous owner hardly drove it, so I drove it a bit to draw down the old gas then put in half a tank of 91 octane. As an aside, yesterday I also put in new plugs and between all of that, I thought it was idling more smoothly.

I also see a lot of people here just seem to use 87 octane. What are the arugments there?

I expect this to have been the subject of another thread at least, but couldn'f find one. If I missed it, please feel free just to point me to the source if this is a rehash of a long beaten-to-death topic.

Thx,
Tim

[narfire]

I use 91 to 94 octane in my 80 FI,depending where I fill and the price of the day.

[rlux4]

I've read that the octane rating in the manuals is the European octane rating, which uses a different rating system than we do. I suspect Canada uses the European method also. They use the RON (research octane number) and the US uses the average of RON+MON/2 (motor octane number). The RON is a higher value than the MON and consequently the US octane rating in our mid grade (87) seems to most closely match the manuals number. A quick Google search on the difference between the octane rating systems would be more detailed for the curious of mind.
Ron (a different Ron than RON)

[pope]

The owners manuals are converted to the units of the countries they are sold in. 91 octane is american not european conversion. That being said, use the gas that doesn't cause knocking, be it 87, 89 or higher. It will save you some money also.

[rlux4]

Makes sense Pope, seeing as the US was the market for the Spider. I use 87 octane and never had a problem.
Ron

[Kingme2]

After filling the TANK in my SUV with the cheapest they sell, the thimble-sized one in my Fiat gets a "fill" of the good stuff. The extra $0.80 for a fill of the good stuff? Sure, why not.

[Tango]

I have noticed on gas pumps in Canada a statement something like Octane is per the R+M/2 method, so it sounds like the same as the US.

Tim

[mdrburchette]

I've always used 93 octane for my early model Fiats but I have been using 87 octane in my 86 Bertone X19.

[So Cal Mark]

we've gone through this discussion before, but use the lowest octance fuel that doesn't detonate. Using higher octance will lower hp. Your car won't run better by using higher octane than needed. You might as well just throw dollar bills out the window while you drive

[mbouse]

agreed.
i used to use the "best" at the pump, until 9-11; when the price gougers went to town and my local pumps skyrocketed to $8.85 per gallon!

i immediately shifted to 87 octane, and NEVER, ever heard a knock. still using 87 octane over 8 years later. if you're gonna throw that money out the window, throw some my way.

[Tango]

OK. I'll go back to the cheap stuff. You don't want me throwing Canadian dollars at you as I pass by at highway speeds, they are metal and will leave a mark.

T

[mbouse]

those loonies and toonies are easier to catch than are the fivers

[velozi]

I found a good balance using 89.

87 was good but noticed that it took longer to start on cold days. 91 felt like a waste of money since I did not notice any improvement compared to 89.

[kristoj]

I use 93 exclusively. But with my model being a turbo, detonation is a much greater issue. In a modern car, you can put pretty much any octane fuel in the tank and the CPU will adjust for it. But remember that Fiat used the (now archaic) Bosch L-Jetronic FI system that does not have a knock sensor and is not capable of adjusting ignition timing. So you really do have to be diligent in paying close attention if your engine is knocking.

[courtenay]

While this is an oldie topic - I'm a newbie owner. I have a crappy cold and have spent most of the day going through the threads on this website - and have learned all kinds of neat things. A question, though, on Octane. We have a gasoline dealer here in the Great Mild North that uses an ethane blend - up to 10% in it's gas. The result is their "regular" has an Octane rating of 90.
The advantage of using these guys is that they are linked into the Auto Club and part of a gas purchase is credited to the annual membership.
The question is - is there any downside with these cars using an ethanol blend? I have an 80 Fi.