Best octane rating for 5.0 MPI

frenchship

Using none ethanol gas wich is best regular fuel or hi test.

212rowboat

All the cocktail that comprises octane does is makes a volatile liquid more inert, and less likely to ignite except when under controlled ignition.. by itself, ethanol has a rand rating over 108 points... On the same scale rating as gasoline, that would be 108octane.. ethanol burns hotter and is hella more corrosive than gasoline, which is why its terrible for engines not made for it specifically...

Adjusting the spark to a much hotter temperature, such as a 55k vdc coil will do, will allow an engine to jump a wider plug gap easier, and make ignition of ethanol more complete and predictable.. removal of soft material from fuel systems will prolong service life of a system made for ethanol.. it will still burn hotter and shorter duration than gasoline, but more powerfully.. and it has that high rand rating w/o adding stuff to it..

For your rig, if you run yours hot, as in temperature wise due to high load and throttle, you'll be better served using a higher octane which will discourage pre detonation.. if you don't run it hard, or live in a higher elevation, you can run low octane and be g2g..

Octane is all about protecting against pre detonation.. if you're not pressing the envelope with advanced ignition timing and your engines don't run hot, and you're running stock spark temperature, save your pennies and use 87/89 recreational gas in your boat.. if you run it hard, live at sea level, and see hotter operational temperatures, use high octanes of 91/93..

frenchship

Thanks Drew Good Infos next fill up I will save a few pennies. Thanks Paul

212rowboat

high octane is needed and required for engines using either high compression or boost (turbo, supercharged), or made with silly high precision...

if an engine detonates before the piston reaches at least really close to top dead center, the piston, wrist pin, rod, cap, and bearing take one heck of a impact from that explosion.. it breaks stuff.. not pretty.. if the engine is lowish compression (south of, say, 9.5:1 compression ratio), there is generally enough margin that it won't catastrophically break (though head gaskets are at risk).. if that same engine is high compression (10.5:1+), it's almost a certainty that pre ignition will bust that engine to bits in a fairly quick amount of time.. one single pre-det could do it to an engine with high compression or in boosted applications..

this is a major reason why you'll rarely see boosted engines that are high compression.. most gas boosted engines are in the realm of 8:1~9:1...

Octane makes gasoline less explosive, or maybe better said, more stable and predictable.. gasoline with high octane less likely to 'splode before ignition spark hits it.. on those high compression/precision engines, it is a necessity.. even on engines running boost that have a low mechanical compression, when boost is introduced the dynamic compression goes through the roof- like, 12:1~15:1... so, it's best to use high octane on those, too..

since you're not running an engine built for high performance, but instead reliability and longevity, chances are it doesn't need higher rand counts to operate safely, and so spending money on high octane fuel is a little bit of a waste..

hope that explains it better than what I previously typed up... :-) 

frenchship

Hey, really good explanation Millions thanks Paul