I discovered that I can buy 100 octane unleaded fuel at a local sunoco gas station. You can directly fill your car with this fuel. They also sell 110 octane leaded gas, but you have to use a gas can. I am curious if adding some to my tank will help the overall performance of my 1969 427 390 hp.  I have always burned 93 octane. The 100 ocatane is not cheap, around $7.00/gal.  Is it really worth the extra cost?  Thanks, Bob

My guess is it's not worth it unless it's a high compression engine that you race.

The higher the octane rating the slower the fuel burns or resists ignition....thus reducing pre-ignition (pinging). If your not pinging you don't need it. So in the big pic, higher octane fuel does not increase HP. It does allow you to make modifications that do increase HP that bring along per-ignition tendencies. The higher the compression ratio the greater the tendency to ping...you will always see the hotted up factory muscle car engines have a higher octane fuel requirement.
Hope that helps you decide if its a good thing for you or not. You can also always blend the stuff down a bit too.
Dave

Thanks for the info. I can always count on getting some good answers from the group

Another plus for the 100 Octane is that it contains NO ethanol. Ethanol if stored in the fuel system over time is destructive on our older cars. Attacks rubber and holds moisture.

I didn't know that about the 100 octane having no ethanol. I kinda have to recant a bit....ethanol make less power...also reduces your fuel mileage. We have it up here at 4800 feet...used to be winter only blend, now its 24/7/365. You can feel the lack of zip compared to 100% gasoline. So you potentially would feel a bit more "zip" with the 100 octane depending on the percent of your blend. You can also dial up a bit more initial timing advance. 14-15 degrees should be no prob for 100 octane. But if you took a trip and could only find 91 octane better carry your timing light.