What Octane ?

[Mike Clayton]

There has been some discussion on another site about what Octane to use, just thought I would put on here and get some "real" opinions. I have always used what Mfg calls for and current run the 87 octane but gas is always treated with seafoam.... should I on from time to time run a higher octane....

Thanks

 

[Randy Walls]

No. In a nut shell due to tuning and compression ratios the octane is set. If you use higher or lower octane it can cause deposits, premature detination (sounds personal!!) and other things. Use what is recomended.



Randy

 

[Scott Hammer TOXIC]

Not to sidetrack but my question has always been why people feel the need to put higher octane in spring when they pull the boat out of storage thinking it will replace any lost octane from sitting. If higher octane is no good due to the lower flash point, then adding higher octane to fuel that has been stored would be the same as watering it down right? Ugggg...glad I never had these problems with my efi. I just changed the lines over, regularly dumped the water seperator, used Merc Fuel Treatment and stabilizer and ran the dog crap out of it. I wouldn't even want to know how many hours were on that Merc 2000 model year efi when I sold it last year and it ran as a smooth as silk and still running the original plugs. Yes it was!!



TOXIC

 

[Berry Lindley]

Tox, I don't add higher octane in the spring, but I do follow the logic. I understand that stored fuel's octane rating will fall, and adding some higher octane to it should average this out some. I keep pretty fresh gas in mine and use it some all year long so I fortunatley do not have these concerns.

 

[Marty Klein]

Who among us is smart enough to know to what octane level the gas has degenerated?

 

[Berry Lindley]

Look, I did not say that this is correct nor exact, but I do understand why someone would do this.

 

[Scott Hammer TOXIC]

But see my logic? Higher octane is b-a-d. It is actually a lower flashpoint made for higher compression and avoids pre-detonation). So if storage causes octane loss and higher octane is a lower flashpoint, then you have achieved absolutely nothing by adding higher octane to the tank. My head hurts....:huh:



TOXIC

 

[Berry Lindley]

They actually do blend and the octane is essentially averaged. The challenge is establishing the octane of the degraded fuel.



Found an octane calculator, assuming 5 gallons of each octane, one 85 and the other 93, the following is a result:





Enter the octane number* and gallons of both fuels:





Fuel 1 Octane Number 85 Gallons 5



Fuel 2 Octane Number 93 Gallons 5





Mixture Octane Number 89 Gallons 10





*For a valid comparison, both octane numbers must be of the same rated type.

(Don't use different octane ratings for the calculation, i.e., an "M" number for

one fuel and an "R+M/2" number for another; keep it consistent)

 

[Bob Bourget2]

Just to set the record straight, higher octane fuel does not NECESSARILY mean it "burns slower". More accurately, the higher octane will withstand more cylinder pressure before ignition. Burn time has everything to do chemical composition as opposed to octane.

 

[Scott Hammer TOXIC]

I thought you were busy:lol: Don't pop in here and confuse me more than I already am:lol:



TOXIC

 

[Bob Bourget2]

Just don't drink the stuff...it's "TOXIC"....:blink::blink:

 

[Justin Lavely2]

Up in these parts we have a choice. 87 octane with ethanol or 91 octane without it. I go for the higher octane all season and avoid the ethanol. SO far so good.

 

[edward hughes2]

In polk co. Fla.we have more and more access to non ethonal fuel,mostly 90 octane,thats what i burn in my Z7.