Ocatane Rating

[1968CHEVYC10]

What are the benefits of running higher octane pump gas? Alot of people I know run it in their older/higher mileage cars. I've got a '75 350 in my '68, It's not original so my guess would be it's got around 100k, it does burn oil. would it be worth the extra $$$ to run 91 octane?

[michael bustamante]

figure mid grade (88 octane) is only 10 cents more per gallon, X17 thats only a 1.70 more for a little bettermilage and cleaner burning gas. It seems worth it to me. When I put in regular unleaded, it seems to burn faster and my engine seems to feel the difference. I dont notice any difference between mid and high octane (90) though

[Stocker]

IMO, the only advantage to using higher octane gasoline is if your engine spark knocks / pings / detonates (whichever term you prefer) on the cheaper fuel.

Older engines, lacking knock sensors and all associated technology & hardware, can be more prone to spark knock, especially if the have higher compression ratios -- or burnt valves that create hot spots in the combustion chamber.

I use whatever the manufacturer recommends, and only use higher octane if the engine pings. My truck (9 to 1 flattops) runs great on 87 octane, as does our Tacoma.

[GRX]

Originally Posted by Stocker

IMO, the only advantage to using higher octane gasoline is if your engine spark knocks / pings / detonates (whichever term you prefer) on the cheaper fuel.

Older engines, lacking knock sensors and all associated technology & hardware, can be more prone to spark knock, especially if the have higher compression ratios -- or burnt valves that create hot spots in the combustion chamber.

Precisely.
Also, excessive carbon build-up can reduce chamber volume thus increasing compression requiring a slower burning gasoline (higher octane) to prevent pre-detonation.

[Longhorn Man]

if you get no spark knock, thrn you are LITERALLY burning your money away for nothing. Octane is nothing but resistance to ignition. It isn't cleaner fuel, or better additives, nothing like that.

[bigsnookmaster]

You only need it if you are running higher compression. It's harder to ignite, therefore reducing detonation. I read an article a couple years ago, with I believe a 565 9.5:1 BBC. It made about 15 more hp on pump gas than race gas. It kinda makes sense. .02

[steves1967]

IN THEORY- low grade fuel 85-87 octane will make more power than higher octane fuel. It does this because the lower octane fuel burns faster, the faster the flame kernel travels the faster the pistons move. Higher octane fuel slows the flame kernel, which slows the piston. However, that low grade fuel that burns fast also permits secondary flames- which we know as ping or knock.

[trz1000]

By the IUPAC definition, Octane is an alkane with 8 carbon atoms.

Oh, you mean the other octane. Basically it's a measure of how well a fuel resists compression ignition. It is not a measure of how volatile a fuel is nor is it a measure how much energy is "in" the fuel (its delta-Hc or heat of combustion). For more info on octane and the chemistry of gasoline, I'm sure Wikipedia has a great writeup on it.