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Discussion Starter #1
Thinking about buying a 636 race bike. Im trying to plan what my future costs will be. My usage would be track days at first and then may do racing later. Mods to the engine include:

Full exhaust and mapped PC
Machined head
port and polish intake

The seller did say you can use 94 pump gas (highest you can find)and will be fine because his engine builder didnt take too much off the head.

BTW the seller used race gas for races and half/half for practices.

I appreciate your comments.
 

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Tito, brutal honesty:

1. why do you have a superbike motor (or worked SS-legal engine) for a trackday bike and learning tool? Why did the motor get rebuilt - damage, or because the previous owner built a superbike to race?

2. I've never raced a stock motor on racegas. There's more to be had in working on braking later and carrying more cornerspeed, getting good drives, and putting money in suspension. Race gas, at 5 gal/weekend/bike is $$ I don't need or want to spend... So I'd not buy a motor that needs it without good reason. My buddy races a 750 that makes 142-ish HP. He races it in Open classes (not 750, so what's the point?)... and the expense of the motor and gas is high. I race a 10R in the same classes for less (though he's a better racer and can outcorner my slow fat ass).
 

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Race gas (I'm assuming VP U4) isn't needed just starting out. The bike isn't holding you back at this point. Later on, maybe but there's plenty of experienced fast racers just running 92 and blowing people away. The extra costs can be spent other places like race tires, track time or racing schools. If you want to run it, here's what I would do.

Take it to a good shop and have them create 2 or 3 seperate maps for pump, 50/50 and full race fuel. Since the engine is modded, having a proper map will give you the best results AND prevent any engine problems from running to rich or lean.

Good luck.
 

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The basic situation is the head has been decked, increasing the compression ratio. You probably will not have a problem with premium pump gas.

calling something race gas is very misleading . There are probably 15 varieties of race gas out there, from leaded 115 octane to oxygenated 88 octane. In your case the higher octane might be better.

If the head is only lightly milled, pump gas should be fine.
 

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Discussion Starter #5
Thanks Ernie.

I appreciate your guys comments, but the reason I'm interested in this bike is not to compensate my inability to ride fast. I'm exploring my options at this point and just wanted to know more info.
 

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If you are within 1 second of the leaders pack and are in contention for contingency money.........sure spend $60/pail to stay with the leaders. If not save your money and spend it on track time and suspension.

[8]
 

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^^ i say save your money on the fuel, it's not worth the extra $5 a gallon if you aren't racing. pump gas will be sufficient. what options are you exploring that would warrant Race gas?
 

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Before ANYONE here can say if you NEED race fuel we need to know your compression ratio. If I had to GUESS based only on the info given I would say no. I doubt that simply mildly decking the head will rase your compression to the realm of needing the octane. As a mater of fact I bet you owuld make LESS power on a 110+ race fuel. If you really want to run it look towards U4. Just remember it CANNOT sit in the tank and lines between weekends.
 

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I use regular fuel, 87 octane and have won several races. If it isn't pinging or knocking you don't need to buy anything different. Octane doesn't give you power, it simply slows the rate of burn to allow a complete burn and most bang on that stroke. If the compression ratio was sigificantly raised you would hear the engine pinging on low octane fuel and then benefit from going higher.
 

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Originally posted by livethedream
I use regular fuel, 87 octane and have won several races. If it isn't pinging or knocking you don't need to buy anything different. Octane doesn't give you power, it simply slows the rate of burn to allow a complete burn and most bang on that stroke. If the compression ratio was sigificantly raised you would hear the engine pinging on low octane fuel and then benefit from going higher.
[:Stupid]LOL...no really our bikes are capable of making a lot more hp on 87 octane w/ PC3. I will post my dyno sheets friday when I complete my tuning for 87 octane map and ignition module.
 

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Octane is simply a measure of a fuels resistance to detonation. Premature detonation is caused by 2 main factors, heat and compression. Those two also tend to go hand in hand. Compression can generally be raised in two ways. Either by changing pistons or by removing material from the head and/or block face (often refered to as increasing the "squish"). There are a couple of other ways to increase the compression ratios but these are the most common. Once you begin to raise the compression ratio you may see a need for a higher octane rating. What this higher rating serves to do is prevent premature detonation of the fuel, aka pinging or knocking (named after the sound often heard from the motor). What happens is the air/fuel mixture enters the combustion chamber and the pistons begins to compress the charge (compression stroke remember?). While compressing the mixture it creates heat. The more compression the more heat is created. This heat combined with the residual heat in the block, head, and piston can cause the fule to ignite before the proper time. The premature ignition can cause severe damage to the motor, often reuslting in catastrophic failure. A fule with a higher octane rating has the ability to better resist premature detonation.

Will running a high octane fuel hurt a motor with out a higher compression ratio? No. Will it make more power? Not always. As a matter of fact it very well may make less. A fuels BTU per pound rating will give an indication of the amount of "energy" contained in that fuel. If the octane rating is higher then the motor calls for it may cause the fuel to ignite poorly in the cylinder. This can cause a slower flame front or incomlete bur in some cases. The best fuel for your stock motor is what the manufactuer calls for.

But what if you have alot of money and want to get EVERY horse from your motor. There are specitality fuels for this. The one that springs to mind and I am most familiar with is U4. But remeber you may pick up 3 to 4 horses but it isnt cheap. You also cannot leave the fuel in the bikes fuel system, it MUST be drined between uses.

All in all if you havent opened up your motor and make significant changes then you do not NEED race gas. If youre not running up front and need every horse to stay in the money spots then the moeny spent on drums of very expensive fuel would probably be better spent somewhere else.

If you have make changes to the motor and think you may have raised you CR then talk to your engine builder and ask them!!
 
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