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Scot said:
I don't run 93. I run 87 in my Hayabusa. 1 point higher that what the OM calls for. If I could find 86, I'd run that-
Come up to some higher altitudes and you can even get 85... oooh... anyways I think the octane rating is a function of altitude but my bikes are high compression so I use th highest octane I can get which is 91 in these parts!

-al
 

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This has got to be the most stupid discussion ever.The modern sportbikes have compression ratios that only pure race engines had just a few years ago. There is no magic involved here. The combustion chamber shapes simply have gotten better and can tolerate thsi swill they call gasoline now days. There is no difference in "burn speed" in gasoline,it is the resistence to detonation. Detonation can destroy a motor very quickly,and even in small amounts slows engine performance by effectively "exploding" before the piston is in position to be blown the correct direction. I will say this simply. If high octane fuel slows combustion then why is 120+ octane used in 13000plus RPM Pro Stock Motors?
For me in every motor I run,unless it has very low static compression,gets high test fuel. The only real test is try pump high test,ride the bike around until the tank is almost empty and fill it up with a lesser octane,preferably from the same brand station. You should notice the bike runs worse,at least on every bike I have tried it on does. Oh, and another thing. After you discover the bike runs like shit,and then go back to high test,try "spiking" a little Cam-2 race gas in. Even the unleaded GT will clean out the motor in short order. The exhaust pipe and every part of the motor will look much better and the performance will "pick up" some more.
 

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Rule #34
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The resistance to detonation is caused by the "retardation" of the fuel igniting. Pre-ignition is what causes detonation. The pre signifies a specific time. (Before) Lengthening the amount of time it takes for fuel to ignite is what the increased octane rating does. This takes the "pre" out of the equation and consequently the detonation with it.

Losts of emotion in the last past. Little information.
 

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sonicrete said:
I will say this simply. If high octane fuel slows combustion then why is 120+ octane used in 13000plus RPM Pro Stock Motors?

Hard to say. Is that motor running a high compression ratio? Does that motor have a large bore and small stroke?

If so, that's why.
 

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Teabagger is a Fat Bitch
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i'm going to beat the dead horse some more here. :deadhorse i was at the yamaha shop this past weekend, a saftey sicker right on the tanks said nothing under 91
 

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OK. For the slow witted out here. Preignition and detonation are different things but the damage done internally is the same.

Preignition is caused by the effect of the compression heating of the fuel mixture and something in the combustion chamber setting it off before the spark. The common things are 1) The side electrode on the spark plug glowing red. This is the reason for copper core side electrode on some brand plugs and the main gain for "push wire" type side electrode.2)Carbon in the combustion chamber glowing. 3) A piece or edge of the headgasket .4) A glowing exhaust valve.

Detonation is caused by the rising pressure created by the moving flame front,igniting the remaining mixture in the combustion chamber. These two or more flame fronts collide.

The power loss/destruction is caused by the detonation/preignition occuring before the piston gets to the top on the compression stroke. The power point occurs approximately 10 degrees after top dead center. This is the point where the timing advance causes the burning fuel mixture raises the pressure to the highest point and should occur so all this pressure contributes to pushing the piston down. A gasoline engine is technically a constant volume process,where a diesel is a constant pressure process. A gasoline engine,all the fuel burns quickly(explodes) at or near TDC. A diesel has fuel injected as the burning continues throughout the power stroke.

If you played with enough engines and fuels you will discover a few things. The typical 87 octane stuff is very "oily". I know this is not reccomended but try to clean off some oily parts in it. There is just no "solvent" action. The fuel is "dead" and does not burn completely in any motor I have found,including lawn mowers. All pump gas is pretty lame these days regardless of the high prices. Any race gasoline will immediately clean out the entire motor and exhaust system. If you dissassemble a motor that runs race gasoline there will not be any carbon,just light grey deposits. The exhaust system will be the same way. I have done this more times than you can count with more brands and type bikes than you can count. Sometimes at the track we run out of gasoline for the electricity generator and sometimes use some race gas for the final few minutes before the track closes. The typical exhaust pipe was black but the generator was running fine. Just a few minutes and it will clean out.

The only argument here is fuel cost, not perfomance. The typical drag race motor has something like 18-1 compression but was based on an older KZ/GS two valve motor. Sometimes the 4 valve top end is better depending on the rules. The combustion chamber ends up being none,ie .040" squish everywhere except for the clearances in the pistons for the valves and spark plug.

A occasionly ride a 4 stroke dirt bike. It has a stock engine,normal compression. Considering the bike gets decent mileage I use race gas in it simply for the improved pulling power. At a point where typical fuel begins to bog down on hills the race fuel will pull nicely. For me the power/perfomance loss is not worth the $2.50 difference in fuel cost.

As a side note here. I have used Cam-2 race gasoline. This is Sunoco race gasoline. This mixes nicely with pump gasoline. Does not change jetting at any mix ratio,so "spiking" a little in any stock bike seems to help. I have also used VP brand fuels. Many dragracers only use VP. I have not had good results using any of the similar brands of VP compared to Cam-2. VP will not mix with pump gas,infact it also will not mix with the Cam-2. The bad effects of the VP was poor repeatabilty of the ET in hot weather. The effect of the bike sitting in the staging lanes slowed the bike down,a lot. The Cam-2 never did this. Most of the guys using/recommending VP store the fuel in an ice chest and only add the fuel to the bike right before the pass. The fuel tanks in these applications are only one pass capacity.
 
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