03sierraslt

iTrader: (22)

The higher the octane rating the higher the flashpoint. Will there be a noticable difference I doubt it, not unless you were to run the stock timing table with like 110 or something.

Quik

iTrader: (7)

youre saying nothing really, maybe 5-8 bucks on a full tank. hardly worth chances of gaskets

Shea

Most newer vehicles have a knock sensor and retard timing when knock is present. The problem is that sometimes you cannot actually hear the knocking yourself. The knock sensors are highly sensitive to it.

What was the factory setting? What is the factory recommended fuel? What vehicle are we talking about there too?

BlackGMC

iTrader: (31)

I think it all depends on the motors compression. The higher the octane level the higher the flashpoint, which some all ready mentioned. The reason some higher compression engines requires high octace gas is to prevent ignition prior to the time that the spark plug would normally ignite it. When gas is compressed it generates heat, if the compression make the cylinder temperature climb high enough the gas will ignite on its own. I think this is why turbo and super charged engines run lower timing because "forcing" more volume the pressure rises on the compression stroke and the heat rises with that said (thermodynamics 101, PV = NkT) you would want the ignition event to happen earlier than a no FI engine before it combusts on its own. So in theroy a FI engine would really benefit from higher octane, cause they could run higher timing. Similar to the way a diesel engine works. This is why you get the "knocking" sound with some engines when running lower octane fuel. The Higher the octane the longer the fuel takes to burn so actually 93 burns slower than 87. Octane does not necessarily make the fuel burn hotter or more efficiently. It keeps the fuel from pre-igniting. Aircraft engines (piston) which are high compression (11.5:1.0 to 12.5:1.0) use fuels with octane levels around 94 - 96 (lower flash points). Our engines are not (well most are not) high compression engines (around 9.5:1.0?). They should run fine on the 87-89 octane range.


Basically the higher the compression the higher flash point you want.


just my .02 cents

Derek @ EDO

iTrader: (73)

yea, just do a lil testin and let us know!

v8

iTrader: (10)

this is the truck in my sig. I do all my logging with auto tap, so I don't have to worry about trying to listen for knock.

fuel trims 0.00 at wot
timing 32.5 at wot
02 reading 880 at wot
IAT 91 degrees ambient temps outside

I hear people talk about running as much timing as possible with 93 octane gas without knock, it just amazed me that with running 89 octane gas there was no knock.

the truck was completly empty when i added the 89 oct. gas, now as for the lower oct. rating it should detonate quicker giving me a cleaner burn or am I wrong?

as far as better times or performance not sure.

the reading from above are the same as if i run the 93 octane gas.

v8

iTrader: (10)

what gaskets are you talking about? heads?

ThunderZ28

iTrader: (7)

I'm glad you can run 89 ....
I put it in my by accident one day, and I thought the piston where going to knock thru the cylinder walls

Quik

iTrader: (7)

yes sir, denotation quickest way to wipe out head gaskets

BlackGMC

iTrader: (31)

Are you running more compression than stock or do you have a radical cam?

(Keep in mind I have been drinking..... Gotta love beer)
I would say that your running more efficiently with 89, which in turn means if you ran higher octane you could run higher timing. just a drunkin thought......