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Im curious if this will help me out or not. Right now the bike is fast as hell, butt in my quest for more power for the dunes i decided i might need to buy a high compression piston. Yamaha has one. My bike has the full hmf and the yz cam , lid off re jetted. What more will this add? Can i still run pump gas? Anyone know any pros and cons it would be great.
 

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Help you out? With what?
Race gas
No cons
 

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Ya, run 91 or 92 in it and ride it hard and that top end will be burnt toast. 110 all the way for a cool engine.
 

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I put my 13:1 in and I have had no problems. I run 91 octane and it has never pinged (detonated) once. The power gain is minimal but it does add a little. I am going alcohol next for a good hp gain.
 

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I will let you know how it turns out because I am going to convert to alky. I am also going to try the web cams (Top end Hp profile.)
 

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I just ordered a 14:1 custom cut piston from sparks racing. I will be running mine on straight 112 now but the power should be awesome. I also sent my head off to ftz to have it ported.
 

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Originally posted by fatspice@Oct 11 2003, 07:45 PM
what would be the displacement of the engine after the 13:1 high compression piston?
changing the piston only doesnt have anything to do with the displacement........ u have to have the cylinder bored than get a larger piston to make up for the extra space in the cylinder............ this piston will only raise your compression, which will give you more torque and horsepower..... but will make you also have to run race gas, which is very expensive....... but it wont change the displacement
 

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When I talked to a guy at sparks racing they had tested the yfz with a 14:1 and they said the power was incredible. They also said porting makes quite a bit of difference. I have heard anywhere from 3-6hp. I can't wait to test mine out at the dunes to see the improvements.
 

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Porting is where a lot of your horsepower comes from too. A lot of horsepower is gained on top end mostly. But if you combine high comp, a good port job and the right cam cobination you could actually bring the horsepower up close to 50 or more! :woo
 
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