Octane Options

[Bulldog9]

Lets talk Octane..... What is the consensus on grade of fuel? I'm running 96 x 71 bore & stroke with .060" deck height 58.8cc chambers in the heads, and flat top pistons with no valve reliefs, and figure my CR is around 8.6:1. I'm thinking I can run regular, but no idea.

I've been running Chevron 92 so far, but dont want to wast $ and leave unburnt fuel residue. The higher the octane, the more resistant the fuel is to combustion, so unnecessary use of 'hitest' is dirtier combustion wise than regular.

I haven't done any experimenting yet, but wanted to get some experience before I do. I plan to run the current tank down to close to empty, then put in 5 gallons of regular and see how that goes, but just wondering.

[GregAmy]

I'm no chemist (and I don't play one on TV) but...one of the tests I do as an SCCA scrutineer is to determine the amount of ethanol in the fuel (we allow 10% max).

The method I use is to take a sample of fuel from the car and pour it into a 100mL graduated cylinder to the 90mL mark. I then pour in 10mL of water. Shake it up briskly and then let it sit. The water will "capture" (whatever the correct word is) the ethanol from the gasoline and a clear line will emerge between the gasoline and the water/ethanol mix. The difference between the measurement of the mix and my original 10mL of water is how much alcohol was in the fuel; simple math (difference divided by 90) tells me what the percentage was.

If this is something you wanted to do yourself, you can, but it presents a couple problems to you:

One, the water/ethanol mix goes to the bottom, but how are you going to decant the gasoline off the top efficiently and at the production levels you're looking for? And what are you going to do with the resulting dregs (please don't pour it down the drain!)

Two, as noted above, ethanol increases octane (which is why SCCA limits max level). If you decant out all the ethanol, you have no way of knowing what the resulting octane of your gasoline is. And it's not a linear add/subtract ratio (i.e., you can't add 50/50 94 octane and 110 octane together and call it 102; it comes out to more like 98).

You're far better off finding a local supplier of non-ethanol fuel. Easier, cheaper, less mess and hassles.

GA

[Mark Henry]

You're far better off finding a local supplier of non-ethanol fuel. Easier, cheaper, less mess and hassles.

That's why I never tried it, in my area 91 premo is pure gas.

Thank's for the info Madswede, I just brought this up because there's a couple guy's doing this on youtube.
I know nothing on the chemistry end other than how to do the simple test for ethanol.