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Discussion Starter · #1 ·
i have recently had my yfz rebuilt with a wiseco 13:1 HC piston and ive been told it may not be a high compression because im using stock battery and that the stock battery wont turn it over if its high compression so im wondering is that true if so im goin to be pretty mad man considering i paid high dollar for the parts i wanted

im running striaght 110 octane gas in it since rebuilt and if its not high compression it will harm my engine right?
 

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You are running high compression. The battery has nothing to do with HC. The person who told you that must be smoking some crazy $hit. Also, 110 is good stuff!
 

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would race fuel 110 and that pump 110 be the same?
 

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Discussion Starter · #5 ·
110 pump gas is the same thing and thats what i use in mine i dont pay 10 dollars a gallon for VP or Klotz or Torco

bout my high compression the guy that told me said that its like weight lifting u can only lift so much weight reffering to stock battery said it wont last long if any at all said that i would have to buy a CBR battery or some other kind that was more juice to turn over the higher compression piston

i still have the stock battery from 2006 and it works great so im worryin if i do have a stock compression or high compression piston
 

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Discussion Starter · #7 ·
this is what the guy who told me said, not sayin he is wrong but im just tryin to get more answers

"the problems that I've experienced on motors with the hc piston is not the initial fire up. But after firing the bike up several times it eventually drains the battery because it only has around 80 cranking amps. Everytime the battery would turn the motor much slower until it eventually stopped turning at all. The motorcycle battery has like 140/150 cranking amps, maybe even higher than that. I have also seen a couple guys get their motors built and think they have one thing only to find out they have OEM parts. Some shops are crooked and pocket the difference in the parts. Not saying this has happened to anyone here but be cautious of this. The best way to tell if you have a hc piston is to do a compression test. A hc piston is around 150psi as a stock piston is in the area of 125psi. Individual #'s will be different give or take. When I was running a hc piston, on the initial build it was 175psi. I was scared to try and crank the bike lol. Once the motor loosened up it dropped down to around 155/160psi."
 

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How are you checking compression? These motors have auto compression releases which should substantially lower cranking compression. I'm amazed that this engine is still running this much compresion with above said.
 

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He is just trying to scare you. He isnt completely wrong but he isnt completely right either.

the stock battery will be fine, the YFZ has an auto decomp system which will bleed out enough pressure to allow the motor to start.

I've had 15:1 compression being started just fine with the stock battery.
 
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