91 octane ????

[kensmith]

Why does my 1978 124 Spider engine require 91 octane per the owners manual? Seems a low compression motor should be OK with 87 octane.

[Exit98]

Well if it doesn't ping under load with the 87 then you are good to go. The only purpose of higher octane is to control detonation.

That said though, I must confess, I use regular in my work-a-day Acura but fill up the Spider with premium.

Just because.

[mikeg]

With regular compression you should be very able to use regular gasoline. My compression is much higher than stock and 91 isn't even quite enough octane for me.

A number of years ago the octane test methode changed as I recall. I wonder if the owners manual is a reference to the old numbers, which again, if I remember correctly were higher than the numbers used today. Or I could have this all screwed up, I'm sure someone will straighten me out if I'm wrong Getting old is tough, maybe it's because my brian is full.

[Exit98]

Yeah Mikeg I think I remember that too. I looked around the web a little but didn't come up with anything definitive in a quick check.

But heck it doesn't matter. Use the cheapest gas you can find that doesn't ping under load is the way to go.

Doesn't matter what brand, they all get their gas from the same refiners/wholesalers.

BTW, you all probably know this but no matter how many levels of octane the gas station sells, they only get delivered two octane levels, the highest and the lowest. The intrium levels are blends of the two. Makes sense when you think about it.

[kilrwail]

The Fiat manual refers to 91 octane RON (Research Octane Number). In the US and Canada our pumps are labeled with the average of RON and MON (Motor Octane Number), which is called the Anti-Knock Index (AKI). MON is always lower than RON so the AKI is between the two. A RON of 91 is about equal to an AKI of 87. I've run 87 octane for 32 years with no detonation and no problems.

[courtenay]

Great explanation, Peter. I've always used the "no ping so it's OK" method to figure out what octane fuel to use and have been running the lowest octane on all my vehicles. I'm not sure whether they have Mohawk stations in Ontario, but out here they pump a gas mixed with 5% ethanol which boosts the octane value of regular to 90. That's what I use, both in my Fiat and Volvo.

[manoa matt]

From what I've read the ethanol lowers the octane level as its less volitle than gas. Most US states are required to include at least 10% ethanol by volume in their gas. The theory is that the US will use/buy 10% less gas from foreign countries, however the addition of ethanol lowers the volitilty of the gas by around 10%, so its a negative gain. Also the amount of energy needed to produce one gallon of ethanol is more than the ethanol can put out.

http://healthandenergy.com/ethanol.htm

[mikeg]

Thanks Peter, that's what I thought I vaugly remembered.

Matt, I couldn't agree with you more. Without starting a political debate, making fuel from food is a remarkably dumb idea. For those that claim you don't have to use corn, make ethanol from some other crop, the point is there is a limit on cultavatable land, so no matter what the crop, it's still using land that either used to or could grow food. When it comes to food or fuel, fuel always wins, as there is more money in it than food, afterall, if you don't have gas for your car, how can you drive to the store to buy food?

Not to mention, there are a number of small engines, your weed eater, chain saw, leaf blower, etc. that do not take kindly to ethanol in their tanks. The 10% ethanol requirement is going to make small engine repair guys wealthy. Even new cars don't really like more than 10% ethanol very well. Older cars don't like it at all.

[mdrburchette]

Here's something interesting about ethanol that kinda makes you wonder why the government considers it a clean fuel:

Ethanol exhaust generates 2.14 times as much ozone as does gasoline exhaust.

Wonder why methanol hasn't been used more since it seems to be a cheaper fuel to produce...other than the invisible flame thing. We run it in our little 5hp Briggs racing engines with no known ill effects.

[courtenay]

Interesting discussion...I, frankly have been using the Mohawk fuel because they give me a 2 cent a litre rebate on my Auto Club membership. I had not done any research on the octane thing. Here's an article that, aside from any environmental
impacts associated with the use of ethanol, is quite interesting.
http://www.fuel-testers.com/gasoline_oc ... l_E10.html

[maytag]

Yeah Mikeg I think I remember that too. I looked around the web a little but didn't come up with anything definitive in a quick check.

But heck it doesn't matter. Use the cheapest gas you can find that doesn't ping under load is the way to go.

Doesn't matter what brand, they all get their gas from the same refiners/wholesalers.

BTW, you all probably know this but no matter how many levels of octane the gas station sells, they only get delivered two octane levels, the highest and the lowest. The intrium levels are blends of the two. Makes sense when you think about it.

hmmmm..... having WORKED at a gas station for many years, (in another life) I can assure you that we did indeed have 3 underground tanks for 3 grades of unleaded, and we received deliveries on my graveyard shift of 3 different grades of fuel.
not that it matters, really.

[baltobernie]

I too think that manufacturing subsidized motor fuel from corn in America is a dumb idea. Erecting a trade barrier in the form of import tariffs on Brazilian ethanol produced from sugar cane is dumber.

But there is some good news on the horizon. The next generation of biofuels will be custom-made. Shell, Exxon Mobil and others are teaming with biological companies to produce "drop in" fuels that will not require blending with gasoline or any other petroleum product. For autos, the leading candidate is butanol. More energy per gallon, not corrosive and low water absorption. Biodiesel, aviation fuel, all in the works.

The enzymes and genetically-engineered bacteria these companies are inventing, combined with fast-growing, sustainable crops such as grasses could yield the equivalent of 1.8 billion barrels of oil without straining the water table, etc. That leaves us 2.5 billion short of what we imported in 2009. Battery cars, trucks and buses in the cities and realistic petroleum pricing could reduce imports to near-zero.

Yah, but somehow I think the politicians will f~~~ up this opportunity, as well