Let it Eat
By: Nate T.
T
he days are getting longer
and right on cue, that
pesky mercury is climbing
higher and higher every
day. It’s quite a coincidence that
we’re also getting into peak riding
season and if you remember some
of my previous articles on heat,
you know that it is not the biker
or motorcyclists friend…unless
we’re talking just getting above
freezing. Most of the time these
heat conversations end up on oil
and keeping that oil cool. However,
there’s another angle here we all
need to think about. Because of
that, I thought it would be a good
time to bring up how to properly
feed your steel horse.
For the most part, scooter
jockeys seem pretty much of the mind that you want to run fuel with as high an octane
rating as possible. Just like a lot of other things I bring up here though, there’s quite a bit
more to it. Some of it may save you a little coin. Some of it may save you a lot more than
that. Don’t worry though. I’m not going to get much into fuel science. I’m just looking to
give y’all a few whys to go with the what-fors you already have on hand.
Before we go down the road of talking about octane though, we need to start out
talking about ethanol blended and non-ethanol fuels. For a bunch of different reasons
that I won’t get into here, the government has been pushing for more and more ethanol-
blended fuels to be distributed across the US as years go on. This isn’t really an issue for
newer bikes because the designers kept that in mind when they thought up the engine
systems for those vehicles. The problems really start to crop up with older motorcycles
that were designed when there was a lot more ethanol free fuel available.
While there are some environmental benefits to ethanol-blended fuel, it has a lot of
drawbacks to the health and performance of your ride. First, there’s quite a bit less energy
density in ethanol blends. This ends up hurting performance while at the same time
creating more heat as it burns. Second, the ethanol in the fuel likes water. In fact, it likes
water so much that it will pull it right out of the air into your fuel system. Then, you end
up with corrosion and the dreaded milky sludge that ends up in the bottom of gas tanks
and float bowls. If you’ve ever wondered why your fuel filter is getting clogged more than
it should, this is probably why. Finally, ethanol will suck out the stuff in your gaskets and
rubber hoses that keeps them flexible. I’m sure every one of you has run into a fuel line
that turned to dust when you gave it too hard a stare.
I know what you’re thinking right now, but I’m not getting into octane quite yet.
Instead, I’m going to bookend the ethanol bit by also giving my two-cents on aviation
fuel. A lot of people I’ve run into think it’s a good idea to put this in our sickles. The
trouble is that this is the stuff that you find at airports that goes in…you’ve got it…
airplanes. For those of you that don’t know, airplanes are a lot different than our favorite
two-wheeled conveyances. So, in spite of those octane rating stickers calling our name
like that special someone from across the bar room, don’t give in. Just like in that bar
room, that av-gas is bringing something extra to the party that you don’t want any part
of. Most avgas in the United States had a lead additive to keep aircraft engines from
grenading…which I’m told is a bad thing. The problem
is that when you run that lead additive through your
scooter, it can end up plugging up catalytic convertors
on later model bikes…and those aren’t cheap. On top
of that, unless you’ve got some crazy, starter killing,
non- pump gas running, monster of a high compression
engine, there is such thing as running too high-octane
fuel…and yup, we’re finally to talking about octane.
If you’re not already familiar, an engine squishes a
mix of air and fuel with the piston as they spin. Without
getting into too many sorted details, the squish both
helps to mix the air and fuel up while at the same time
putting the right amount of pressure on it so that when
the spark plug fires, the mixture will burn efficiently.
Higher performance engines tend to squish the mixture
a lot harder. That’s all fine and dandy until you realize
that the added pressure can actually make the mixture
ignite before it’s supposed to. That’s a bad thing. When
you hear people talking about knocking, pinging, or
detonation, this is what they’re talking about. This is
about the same as your piston hitting a brick wall and
can be from mildly annoying to running-over-your-
flywheels inconvenient. This is where choosing the
right octane fuel becomes very important.
The octane rating of a fuel is its ability to resist igniting
too early because of excess heat or high compression.
This resistance also means that there’s more energy
stored in higher octane fuel. This doesn’t mean that
you can just add jet fuel to your bike to give it rocket
power. It doesn’t work that way. Your engine is set up
a certain way that requires a certain octane fuel. If you
use too low an octane rating, then you get detonation.
If you use to high an octane rating, you can make less
power because the engine doesn’t have the chutzpah
to burn it completely. On top of that, an incomplete
burn means extra soot and other garbage building up in
places that’ll mess up airflow more and more over time.
The bottom line here is that you need to be feeding your
engine the octane fuel it needs…not what you think it
needs. Most of the time, if you’ve somehow managed
to leave your bike stock, then the owners’ manual will
tell you what octane fuel you should be running. If you
bought the motor aftermarket, ask the manufacturer
what to run. If you’ve had the motor modified or built
from scratch, then your builder should be able to tell you
what it wants to eat. Regardless, don’t use the octane
of your fuel as another way to bar stool drag race. Go
out there and run your bike like it should be run. Until
next time, keep it between the lines and shiny side up.
Shovel on.
22 Thunder Roads Magazine Louisiana/Mississippi | July 2018 | www.thunderroadslams.com
www.thunderroadslams.com | July 2018 | Thunder Roads Magazine Louisiana/Mississippi
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