TLRMan- I know what I am talking about and I am sure that since you have built motors before you have seen what can happen when you run a low octane fuel in a high compression motor. I've seen snapped connecting rods and shattered pistons because people throwing lower octane fuels in high compression motors. I've built motors that have called for premium when they were stock with just a 10:1 ratio and needed 101 when I was done with them. My bike has an 11.5:1 ratio and it calls for premium. My truck only has 9.4:1 so it gets 87. Everything I have either owned that was stock or I built up with a 10:1 or higher gets premium, and lower than that and it gets low octane.
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Originally Posted by Kurlon  All depends on the motor, and what you consider 'higher compression'. Modern head and piston design is MUCH better than what it used to be, so while in the past anything over 9:1 would demand high test to run without pinging, you can build a 12.5:1 motor that'll purr on 87 octane fuel now. So, if you want the best performance, run the lowest octane you can that doesn't ping, simple as that. |
That's true for older motors. Newer ones will retard the timing if it starts to knock.