To find out why you can run 87 (vice other octane levels), you need to understand what octane actually does.
Caveat: This is SIMPLE TERMS. You engineers and builders can debate me if you wish, but let's not get wrapped around the spoke for our new member.
Simply, Octane SLOWS the burn of the fuel thus cooler. 92 burns cooler than 87. Many engines, especially high compression engines, "ping" or "detonate" - some call it "dieseling". In truth, these are all the same terms but different issues. Lower octane fuels burn hotter, if the piston or squish area of the cylinder gets too hot, the fuel/air mix ignites at the wrong point in the stroke (rather than when the plug sparks). If the ignition is during the up stroke, serious damage usually occurs. Engine builders usually build an engine within very specific tolerances and with higher compression you have higher heat.
As you can see, there are many reasons you get away with 87 and that is great if you are not detonating. That means you can save a lot of money on fuel and put it to other uses. But be aware that you could also be causing damage to the engine that could be terminal. Get a good read of the piston often until you are sure of you jetting and engine temps.
