On 6/6/2019 2:57 PM, Randall wrote:
>
> Those brass needles are really soft; I would suggest a fine tooth file and a
> light touch rather than a Dremel. I haven't worked out how big the flat
> should be, but it won't take much. You're only looking for something like
> 5% more fuel (or maybe 6%, depending on whose numbers you believe).
>
> Again assuming you want to run E15 in the first place.
>
The calculation is .85 x 115.5 + .15 x 76.0/115.5 = 0.94874, nominally -
5.125%. But, there are other considerations. The latent heat of
evaporation of alcohol is pretty high, so the flame front will propagate
a bit more slowly, which means the advance can be raised slightly. And,
since the octane rating for ethanol is 110, the compression ratio can be
raised slightly with no ill effect. Both of those effects translate to
slightly better mileage, or at least mitigate the loss in fuel value.Â
The octane increase is not insubstantial. If the gasoline in the blend
is 87 octane, the total blend with 15% ethanol is 90.5.
Anyone operating at altitudes well above sea level will probably see a
slight improvement in performance, because of an oxygen atom in the
alcohol molecule, presuming that all else is right with the engine
(i.e., mixture correct and timing adjusted for altitude).
The bugaboo, I suppose, is that some people may still have rubber hoses
installed that aren't alcohol-proof, and that's something that would
have to be corrected. Buna-n (nitrile) will work, but with shorter
life, but neoprene or SBR (styrene-butadiene rubber) would have good
resistance to alcohol and are readily available. Anyone contemplating
replacement of rubber hoses with braided stainless steel w/Teflon liners
should avoid that. Nylon or XLPE liners are fine.
But, in general, go easy on needle mods. For SUs and Strombergs, simple
mixture enrichment and a little fiddling with the advance may get one
most of the way there. Plug cuts will tell the tale.
Cheers.
--
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....
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