Octain
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Senior User
Joined: Mar 2004
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From: FT POLK LA
Octain
What would be the best Octain to use with the FI 302?
It has 216,000 miles on it and I currently run it on 89 since it doesnt run as well on 87.
What would be a good additive to use if any?
It has 216,000 miles on it and I currently run it on 89 since it doesnt run as well on 87.
What would be a good additive to use if any?
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
The best would be lowest octane you can run without excessive pinging.
As an engine wears out, the rings allow more oil into the cylinder, and worn or hardened valve stem seals can allow oil into the combustion chamber. Excessive oil contamination in the chamber will aggravate pinging, so an engine's octane requirement can increase as it gets older and wears out.
The main reason why lower octane is better is because it is less expensive.
Another benefit of lower octane fuel is that it has more specific energy (i.e., energy/mass) than higher octane fuel. Most octane enhancers now used by refineries in the US are oxygenated hydrocarbons (such as methanol). As you know, combustion is an oxidizing chemical reaction, so oxygenated hydrocarbons are effectively a partially burned fuel, which has less potential combustion energy than non-oxygenated hydrocarbons.
Unless an engine is calibrated to benefit from more advanced ignition timing (what most performance chips do), there is no performance advantage to using a higher octane than the minimum necessary to prevent pinging.
As an engine wears out, the rings allow more oil into the cylinder, and worn or hardened valve stem seals can allow oil into the combustion chamber. Excessive oil contamination in the chamber will aggravate pinging, so an engine's octane requirement can increase as it gets older and wears out.
The main reason why lower octane is better is because it is less expensive.
Another benefit of lower octane fuel is that it has more specific energy (i.e., energy/mass) than higher octane fuel. Most octane enhancers now used by refineries in the US are oxygenated hydrocarbons (such as methanol). As you know, combustion is an oxidizing chemical reaction, so oxygenated hydrocarbons are effectively a partially burned fuel, which has less potential combustion energy than non-oxygenated hydrocarbons.
Unless an engine is calibrated to benefit from more advanced ignition timing (what most performance chips do), there is no performance advantage to using a higher octane than the minimum necessary to prevent pinging.
Cargo Master
Joined: Oct 2003
Posts: 2,833
Likes: 4
From: Jefferson, Iowa
On the same topic, here in iowa, we have 89 ocatain with a 10 percent blend of ehtonal. 87 octain is 2 cents more expensive. Would i get better MPG with the 87 or the 89? The 87 is 100 gasoline, but the 89 is gasohol. What do you think?
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