mark524
Expert Class
Posts: 297
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posted June 26, 2007 06:36 PM
How does 87 octane make more power?
I keep reading about how 93 octane actually takes away power. I don't understand how that's possible. I've put 93 in all my bikes just because I never knew how low I could go and avoid detonation. I know that you won't gain power with octane unless you tune for it, but I don't see how on a stock bike 87 makes more power than 93. Please explain
  
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Mi11z
Parking Attendant
Posts: 16
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posted June 26, 2007 06:37 PM
Ive never heard of that, ive always put 93 in mine also
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mark524
Expert Class
Posts: 297
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posted June 26, 2007 06:41 PM
look in brock's diaries. He says something like " I hate 94 octane, it kills power." It's part 1.
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mark524
Expert Class
Posts: 297
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posted June 26, 2007 06:44 PM
 Edited By: mark524 on 26 Jun 2007 19:45
http://www.dragbike.com/dbnews/anmviewer.asp?a=2079&z=2
4th paragraph
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MasterBlaster
Expert Class
Posts: 297
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posted June 26, 2007 06:49 PM
The higher the octane, the more additives and less actual fuel. Less fuel equalls less energy.
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fastestbusaaround
Needs a life
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posted June 26, 2007 07:19 PM
I thought that higher octane meant delayed explosion, resulting in less detonation, resulting in lower power?
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BlackMagic14
Needs a job
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posted June 26, 2007 07:22 PM
FBA is essentially correct I usually run 89 and it is a noticeable difference then 93... I bet Smokin could give a more detailed answer
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Mi11z
Parking Attendant
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posted June 26, 2007 07:43 PM
so would 89 be better then 110?
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fastestbusaaround
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posted June 26, 2007 07:46 PM
Ya think?:d
MR9 is 87 octane...
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gms118
Expert Class
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posted June 26, 2007 07:50 PM
I have heard this before, but i didnt believe it. I think its worth a try.
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Mi11z
Parking Attendant
Posts: 16
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posted June 26, 2007 07:53 PM
I have heard this before, but i didnt believe it. I think its worth a try.
+1
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BrooklynNYZX12
Zone Head
Posts: 520
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posted June 26, 2007 08:27 PM
With the newer design cylinder heads,using higher octane fuel has a similar effect on horsepower that retarding the ignition timing would have.So putting 93 in a bike that requires 87 would actually take some horsepower away.Entropy might be able to explain this better but a higher octane fuel is more resistant to burning/combustion than the lower octane 87's are.The higher octanes in essence burn at a slower more controlled rate.I think the advanced cylinder head/engine combos that the manufacturers produce don't require this higher octane to make power.VP MR9 probably makes the most horsepower out of all the aftermarket fuels,I think the octane is 87.When the engines are modified with very high compression ratios I think the need for higher octane would be required.I can't explain this technically,some of the experts would have to weigh in on this.D.Meyer,Entropy.
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Nelson Taylor
Zone Head
Posts: 927
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posted June 26, 2007 08:33 PM
I ran 93 in my bike when I first got it and have never ran it again. 87 is all my bike see's when racing. Brooklyn got right, 87 burns faster than 93. Now for long distance rides I would use 93.
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BlackMagic14
Needs a job
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posted June 26, 2007 08:52 PM
If you are using nitrous you need a high octane fuel but as far as on motor I think the 14 can handle 89 easily i havnt gone as low as 87 just not one hundred percent sure there will be no detonation and I dont wan to risk it
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SteddyTeddy
Pro
Posts: 1664
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posted June 27, 2007 04:30 AM
Edited By: SteddyTeddy on 27 Jun 2007 05:38
quote:
I have heard this before, but i didnt believe it. I think its worth a try.
You better believe it! We prove it at the drag strip all the time. If you do some searching you will find a couple sites that explain it in full detail. Simple answer is, higher octane fuel is harder to detontate and burns slower. It it used in high compression motors to keep them from predetonating. With heat, high compression and low octane fuel, a motor can bacially detonate the fuel without a spark. You want to run the lowest octane you can get away with without hearing that octane ping. That ping is very bad on a motor.
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V2K_CCTX
Expert Class
Posts: 259
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posted June 27, 2007 04:34 AM
Effects of octane rating
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).
Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitues the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Octane rating is a measure of detonation resistance, not deflagration characteristics.
It might seem odd that fuels with higher octane ratings explode 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 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 that carbon-carbon bonds contain more energy than carbon-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 (per litre 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) into ethanol. 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 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 volume 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 (about 20 MJ) of energy, where ethanol run at its preferred max power mixture of 6.5:1 will liberate approximately 24,400 BTU (25.7 MJ), and Methanol at a 4.5:1 AFR liberates about 27,650 BTU (29.1 MJ).
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 energies 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 falseĀengines 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 or even imaginary.
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-revving 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: [1] . 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.
The octane rating was developed by the chemist Russell Marker. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.
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87gtNOS
Zone Head
Posts: 620
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posted June 27, 2007 06:00 AM
ok, perhaps a dumb question sitting here at my work desk....
But what octane is the recommended for the ZX14?
I assumed it was 91+ , so that is what I have been running. And yes, I FULLY understand about fuels and octane ratings, etc....
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07 ZX14 - YEAH BABY!
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V2K_CCTX
Expert Class
Posts: 259
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posted June 27, 2007 06:57 AM
The rule of thumb has always been, run the lowest octane you can and still not knock/ping detonate. Sounds lik emost here are running 87 or 89. Will try lower octane on my next tank!
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bigdtd
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Interceptors
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posted June 27, 2007 07:00 AM
it has been discussed at length, the high octane burns slower and is less likely to detonate, the manufacturer recommends it and it gives extra protection against engine damage(pinging) with some power sacrifice
detonation occurs with high compression or heat more frequently
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raband
Expert Class
Posts: 121
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posted June 27, 2007 07:08 AM
quote:
The rule of thumb has always been, run the lowest octane you can and still not knock/ping detonate. Sounds lik emost here are running 87 or 89. Will try lower octane on my next tank!
Don't most modern engines/ecu's have knock sensors that adjust timing etc accordingly for the fuel used? Running a lower octane may be fine and not knock, but the engine could have adjusted accordingly by retarding timing a bit?
Haven't noticed on the 14 yet, but often in my car or when I had the XX I'd be noticing a lack in power and remeber back to filling up with a lower octane fuel. Was interesting in that it wasnt me trying lower octane and seeing if I noticed the difference, but was by noticing a difference and then working out the reason - sort of a blind test. Was actually noticable in the real world.
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fastestbusaaround
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posted June 27, 2007 08:40 AM
My 10R knocks if I go lower than 91, so the ECU doesn't make up for that...doubt that the 14 does either...
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ninja_knight
Zone Head
Posts: 666
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posted June 27, 2007 08:54 AM
If you have been using 93 octane for months and your bike hasn't seen anything else, will you damage the engine by suddenly switching it to 87? Kind of like switching someone to decaffeinated out of the blue without their knowledge?
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ouijonbu
Novice Class
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posted June 27, 2007 11:46 AM
alcon,
The makers of the bike call for a rating above 90, so does this mwan we run 87 or what. someone put this in leymans terms.
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