increasing the octane of my gasoline with ethanol

I don't know what kind or how old your bike is but, most everything sold here in the US since the early seventies can run well with what we now call 89 octane which is a middle grade. You need to keep in mind that some recommendations were made under the old rating system in which premium gasoline was at least 98 octane and many times 100+. Those older vehicles sold with the 97+ octane ratings under the old system run well with todays 93 octane sold as premium gasoline. The reason for this is that the current rating system uses the average of the research and motor octane ratings. If you have a ping problem, you should make sure you have the correct heat range spark plug installed, make sure you have the timing set correctly and that the advancer unit is working correctly. Make sure you do not lug the engine causing it to overheat. One proble I have seen on motorcycles/motorbikes is trying to gear it too tall which does not allow the engine to run in the correct rpm range for the load. Make sure you have the correct sprocket set. If you have those items covered, Octane 104+ may be what the tech ordered for the problem.

Good luck Lugnut

It's (of course) a 4 stroke, Honda MRX 125. Bought it one year ago as brand new and it's used by me on the Philippines. I assume they come out of the shop with all the original and recommended parts, which should include the spark plug and sprockets. The 95+ there is sold as 'research rating' (although I don't understand what's the difference between 'research' and motor ratings). Timing seems correct judging on the position of the markers on the flywheel.

So, I'd like to experiment a bit trying to increase the octane rating if possible with some additive. So, to repeat my question: Is there a calculation I can apply to determine how much ethanol I should add to the 95 gasoline to obtain a mixture with an octane rating of 98? If it doesn't work, then at least I'd have had the fun of the experiment.

thanks, shakiro

The number of carbon and hydrogen atoms by volume is different for alcohol vs. gasoline, also ethanol carries oxygen atoms where as gasoline does not. Basically, you would have to recalibrate your carburetors for the mix you decide upon, and then run that mix all the time from then on out.

nate

You could do it by trial and error, starting with a simple normalization formula:

Ethanol has octane ratings of about 129 (RON) : 102 (MON)

x(129) + (100-x) (95) = 100(98) When you solve for x, you get about 8.8 % ethanol needed.

Try it and see. You may be able to wean it further if you like. Might be better to drink the ethanol and use one of the commercial octane improvers.

ok, fair enough, but I think the amount of recalibration needed would also depend on the amount of ethanol mixed with the gasoline. And that was exactly my question: Is there a calculation I can apply to determine how much ethanol I should add to the 95 gasoline to obtain a mixture with an octane rating of 98? Of course 'from then on' is not so absolutely as it sounds, because one could always decide to 'roll back' the recalibration.

shakiro

Yes, that's what I mean, thanks, so the octanes add up linearly.

No issue, you won't believe how cheap ethanol is on the Philippines, one can get 1/4 liter rum (almost drinkable :) for 35 Philippine pesos, that's

Never seen those...

shakiro

Maybe not linearly, but close enough for first approximations.

Toluene is probably a better octane booster as it will not need adjusting the air to fuel mixture.

See:

Are you familiar with what are regular additives to increase ON?

shakiro

nice post! thanks

shakiro

My '71 Triumph Bonneville loves avgas.

Also consider methanol as an octane booster. It is generally cheaper than ethanol. The downside is that it may be more corrosive to your fuel system, so you may have to take extra pains to clean system periodically, depending on materials used in the fuel system. The octane values of ethanol and methanol are very similar, so same proportions should work. To take full advantage of boost, you may have to richen mixture a bit.

Oh, forgot to add formula. I believe both ethanol and methanol are in the 125 to 130 range. You do math- try simple ratio, A x (gasoline octane) + B x (alcohol octane) = desired octane, and A+B = 100, if A and B are in percent.

What is 'avgas'?

shakiro [snip>

Thanks, I don't need extra boost, could even function well with a bit less. But the corrosion would be a problem. I'll see what to do.

shakiro

ok, thanks.

shakiro

I believe they are referring to aviation gasoline...or airplane gasoline.

Ah ok, retrospectively I'd be inclined to say: "Ah yes, of course!" :)

shakiro