Main Motorcycle: Triumph Thunderbird ABS
Join Date: May 2012
Location: Pittsford, NY USA
|Thunderbird Twin - Technical Talk Technical talk for the big Thunderbird twin|
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You may be right but how does a mole of isooctane have the same heat of combustion as a mole of ethanol? They change the blend seasonally here so when they add 10% mtbe, do they boost the octane rating by replacing some benzene or hexane with heptane or isooctane?
In Australia our fuel octane ratings are:
Unleaded (ULP) 91
Premium Unleaded (PULP) 95
High Performance Unleaded (typically BP Ultimate, Shell Optimax, Vortex 98) 98
I personally run BP Ultimate which is 98 octane. It is a cleaner burning fuel and lays down less deposits inside the combustion chamber for not that much extra cost.
Some comments here about higher octane fuels causing harm to the Thunderbird engine are wrong. The higher the octane number the higher the fuels resistance is to detonation which is an uncontrolled ignition or pre-ignition of the fuel before the controlled ignition from that of the spark plug. In actual fact running higher octane fuel in an engine designed for lower only hurts you in the back pocket because of the higher cost. The reverse is true though in using lower octane fuels in an engine designed for high octane but using low octane instead. That is when real engine damage occurs. And that is because the low octane fuel will ignite prematurely as the generally higher compression (and therefore higher heat) ignites the fuel while the piston is still on it's compression or up stroke causing the ignited fuel to push back against the still rising piston. This will cause detonation or pinging in most engines but in worst cases things like push rods bend and sometimes pistons fail etc. To correct Lantesh with his comment on octane rating it is not the fuels resistance to ignition but rather the fuels resistance to detonation. The spark from the spark plugs will ignite both standard and higher grade octanes on queue. It is no more difficult to make the ignition of the fuel to happen for the engine with either octane but the higher octane will resist the uncontrolled pre-ignition when it is not meant to happen.
So in summary the higher octane fuel is better for the engine and not harmful. If the Storm or the big bore 1700 engine has indeed a higher compression than the 1600 engine then it will benefit more so than the standard bike but trust me the 1600 (like mine) will still burn all the fuel injected into it's chamber when the spark plug tells it to but will do it with less deposits left behind by using 98 octane fuel.
Ok someone just hit one of my pet peeves...personally, I think that the current dyno trend closely resembles something secreted from the north end of a southbound male bovine.
I worked in the first shop in my area to have a dyno. At the time I loved it. I would get an engine close, then ride it and fine tune the bike. Now people are obsessed with the top number. 99.999% of them do not even know what they are looking at, when they see the chart, or at what point the horsepower and torque curves should cross. Dynos have become the crutch of those who really could not tune an air fuel mixture and a timing advance curve otherwise.
The first thing people should realize about a dyno is that the horsepower curve is absolutely useless for street. if you are looking for that peak number, you are one of the people who does not know what they are looking at (sorry to be so blunt, but it is true). That number is only pertinent at a very very narrow RPM window. One that you very rarely ever see on the street.
One fact that very few people realize is that real engine builders only use the horsepower peak to set the rev limiter. it means nothing else to the builder. What Carrol Shelby said about horsepower selling cars, but torque winning races was absolutely true. it is the torque curve that makes you feel like the acceleration is going to dislocate your arms and peal the skin off your face. Torque is what makes a bike or car feel fast. Tuning in a good torque curve is what makes a satisfying performer. When you just look at horsepower the engine is "peaky" and feels like a weak two stroke. The engine builder knows this and knows that power is always a compromise. You trade off a little peak power to make it pull harder through a wider RPM range
on my own daily rider, I have an air/fuel meter. I adjust for proper air fuel ratio for what I want the bike to do. If my mixture is perfect, what can dyno tuning do for me, besides print out a paper, with a result I all ready know?
this is true, to a point
what you say about octane being a detonation retardant is 100% true. Octane does not change the burn rate of gasoline, only the flash point at which it ignites. There is absolutely no reason to run fuel with a higher octane rating than what is necessary to suppress preignition. What that means in Layman's terms is that if your engine is not "pinging" there is absolutely no gain in running higher octane gasoline.
All the old bench racing stories about someone's brother's friend's cousin putting racing fuel in his car/motorcycle and gaining enough horsepower to beat every other car in the county, are just that. Bench racing STORIES.
For those who want a little more out of their bikes, there is some room to "tune" an engine though. Factory ignition curves are often made "foolproof" . Meaning that any fool can operate within these parameters. If you choose to run higher octane gasoline all the time, you can advance the timing, and run a more aggressive advance curve. This does give more power and a better throttle response
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