Octane rating needed?

[fred cook]

The engine in my SC is now a 3.3SS w/10.1:1 pistons, 964 cams, Carrera heads and Electromotive XDi twin plug ignition. With this setup, the timing advance is set at 25 degrees compared to the 36 degrees required for a single plug engine. As noted, the compression was raised from 9.3:1 to 10.1:1. With the relatively mild compression bump and the reduced timing advance, do you think this engine requires premium fuel? The original SC engine was rated to run on 87 octane unleaded fuel. I'm wondering if this engine could do the same? Your thoughts on the subject will be appreciated.

[mamaj]

I rebuilt Harley engine a few years back and upgraded to 10:1 pistons, hotter cam, sent heads to California to Branch Flowmetrics to change combustion chamber, enlarge valves, port and polish, etc.. They did extensive flow testing and dyno runs with their products. Their strong advice was run higher octane to help with pre-detonation but also the higher octane helped engine run cooler.
We also run aircraft engines on airboats here in Florida and advice from aircraft mechanics, was the same, regarding the operating temperature. Since we are in Florida heat and operating at sea level and not 5000' up, where air is cooler, we run 100 octane LL. even though some older engines were rated for lower octane.

[Elombard]

One thing I read on the internet the other day..... the 93 we can get here does not get moisture build up when it sits and cause fuel system degradation as much as the lower grades. This is supposedly because the ethanol stays in solution better. Important for cars that sit up some....I have no idea if that is true but I have been running premium for several years and no fuel issues. I only drive it once or twice a week most of the time.