Quote:
Originally Posted by RedJewelSS
yep, just look at diesel. twice the BTUs of premium gas and less than half the octane rating.
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This is a bit misleading.... Octane doesn't matter with diesel. the main component diesel uses to resist combustion is Cetane. Static compression ratios are completely different for these types of engines. gasoline engines are typically 8-10 (although we're seeing production engines hitting 12's sometimes now) and diesels are more into the 40's.
Octane and Cetane levels represent the fuels resistance to combustion under compression. The higher numbers will resist it longer so you can squish it more and get more "work" out of it.
The reason the v6 recommends 87 and the v8 recommends 91+ is most likely the Dynamic Compression ratio. Which has everything to do with your cam/valve/timing setup. I'm willing to bet the v6's dynamic ratio is much lower than the v8's. (I don't actually know the numbers)
Static ratio is a good rule of thumb to gauge where you should start with octane, but dynamic ratio is the more realistic number and will really determine what your engine is happy running with.
edit* I didn't finish reading the thread before I posted this... lots of good info here already that I repeated