93 octane vs 87 octane


basscrazy

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#1
I have been using 87 octane in my tank since I bought my busa. While riding today a friend of mine who rides a busa said my bike sounds funny. I told him thats the way my bike has always run. After a long high speed run, we stopped at the Sunoco station. (I was running on fumes) I reached for my normal 87. He recommended that I should try the 93. I did. My bike sounds cleaner (It's really hard to describe it except to say cleaner...) But the throttle is what impressed me. My bike has more pep. My baby has always run, but she runs better (very obvious...) So my question is why??? I have read all the posts about waisting money using the 93. The bike is not optimized to handle 93... ...and that the manual recommends 87. I am here to tell ya my bike runs better using 93. This was obvious to my riding mates. My bike is stock except for the PCIIIusb and Yosh Carbon RS3 bolt-ons. My map is the Yosh bolt-on map from Dynojet...... What gives???
 

Charlesbusa

Used to be a SoCal Busa
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#4
The stock busa is made to run 87.

After modifying the fuel map, it could be whatever you want. If you want it to run good on 87 again, take it to a dyno and have an expert make a custom map. Running the baseline map from dynojet's website is going to be perfect for your bike.
 

tinbender0

Cool Breeze
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#6
I'm running the same cans fom yoshi and map from commander.  I've never tried the regular gas though, I don't know why?
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?
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?? I guess you think more money for the gas so, It must be better....
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qball

Registered
#7
You say stock bike, but Power commander is a change to the fuel mapping. I think we have had this posting before. Your bike may run better with 93, Stock bike 87 is what the Suzuki set it up for.
 

V8N3T

More mods plz..
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#8
so a stock busa, and when I say stock I mean NO MODS to the fuel mapping, airbox, PC3...etc. I mean stock, no slipons, nothing....runs better on 87 than 93? Is this proven on a dyno result? or just speculation on what the MOM(motorcycle owners manual) says? Im just curious myself. Would like to see some numbers on a DYNO 93vs87 octane just for sh*ts and giggles.
 

qball

Registered
#9
Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression ratio only governs the maximum compression that can be achieved).

It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation (pre-ignition = engine knock) as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.

A simple explanation is the carbon bonds contain more energy than hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content on a volume basis (ie per liter or per gallon). The reason for this is that ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl radical for a H hydrogen which transforms the gas ethane (C2H6) (which is an alkane) into ethanol (which is an alcohol). Note that to a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

In the case of the alcohol fuels, like Methanol and Ethanol, since they are partially oxidized fuels they need to be run at much richer mixtures than gasoline. As a consequence the total amount of fuel burned per cycle, counter balances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred max power air fuel mixture of 12.5:1, it will release approximately 19,000 BTU of energy, where ethanol run at its preferred max power mixture of 6.5:1 will liberate approximately 24,400 BTU, and Methanol at a 4.5:1 AFR liberates about 27,650 BTU.

To account for these differences, a measure called the fuel's specific energy is sometimes used. It is defined as the energy released per air fuel ratio. For the case of gasoline compared to the alcohol fuels the specific energys are as follows.

Fuel Net energy Units
Gasoline 2.92 MJ/kg
Ethanol 3.00 MJ/kg
Methanol 3.08 MJ/kg
Using a fuel with a higher octane lets an engine run at a higher compression without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure, which is a function of elevation and weather conditions.

Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine power is a function of the fuel as well as the engine design and is related to octane ratings of the fuel... power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved.

Many high-performance engines are designed to operate with a high maximum compression and thus need a high quality (high energy) fuel usually associated with high octane numbers and thus demand high-octane premium gasoline.

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is mostly false—engines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal.

Using high octane fuel for an engine makes a difference when the engine is producing its maximum power. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. Depending on the engine design, this particular circumstance can be anywhere along the RPM range, but is usually easy to pin-point if you can examine a print-out of the power-output (torque values) of an engine. On a typical high-rev'ving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder; although the cylinder is already rising at the time the intake valve closes, the forward speed of the charge coming into the cylinder is high enough to continue to load the air-fuel mixture in.

When this occurs, if a fuel with below recommended octane is used, then the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a white paper that gives an example: [3] . In this example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load then the difference in octane will have even less effect. The example cited does not indicate at what elevation the test is being conducted or what the barometric pressure is. For each 1000 feet of altitude the atmospheric pressure will drop by a little less than 1 inHg (11 kPa/km). An engine that might require 93 octane at sea level may perform at maximum on a fuel rated at 91 octane if the elevation is over, say, 1000 feet. See also the APC article.
 
#10
you wouldnt think so but sometimes that seat of the pants feel you experience can be less power than you started with. only way you can prove a feeling is to have it dynoed once with 87 and once with 93.
 

V8N3T

More mods plz..
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#11
thanks for clearing things up, after reading that I now understand the common missunderstanding of gasoline.
 

Got-Busa?

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#13
If you didn't have it dynoed before/after or take it to the track, there is no way to know for sure.  Seat of the pants can do anything on any given day depending on weather.....
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NightCrawler

Love all. Trust a few. Do wrong to none.
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#19
The Busa will run with any pump gas. The manual says MINIMUM 87 octane ... that doesn't mean its the best fuel for it though. My bike runs best with 93 just as basscrazy stated. It idles much smoother and I get no jerks when taking off from a stop.

I see it like this ... if you go to a sporting event where the cheapest ticket is $20 and the most expensive ticket is $1,000, which will provide the better seat? Sure both tickets will allow you to view the live event just like both octanes will get the Busa moving, but would you really want to settle for minimum? Heck ... in grade school you can actually pass a class if you get straight "D"s. How would you feel if your child brought home nothing but "D"s though? "Minimum" seldomly means "best".

Bottom line, if you see no change going from 87 to 93, then save your money and go back to 87. But if you see the bike is running better with 93 (which I did), then keep running it. Again ... 87 octane is the MINIMUM, as long as you don't go under that you'll be fine. Plus and premium will cause no damage.
 

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