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I purchased a cp piston to rebuild my 06. I wanted to avoid having to run race gas and from what I have read hear in this forum 12.5:1 is the highest you should go on pump gas. with the difference from 04-05 to the 06 head I was told to get a 13:1 cp and this would work out to 12.5:1 in my bike. the mechanic who will be doing some of the head work (port/polish and valves) said I would have to run race gas with this piston.

what do you gurus say????
 

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if the pistons were rated for the 04/05 bikes then I believe it is correct that the 13.1 should work out right. But I am not positive.
 

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a 13:1 in an 06 will equal 12.5:1: PUMP gas safe.

PDR[/b]
yup, plus depending on how much material he removes from the combustion chamber that will also lower the comp ratio some, you should be good.
 

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so in a 06 if you run a 13.5:1 hc piston it equals to 12.5:1? how does that work? so what does a 12.5:1 hc piston come out to be and what is the compression of a stock 06 piston?
 

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so in a 06 if you run a 13.5:1 hc piston it equals to 12.5:1?[/b]
no, see below

a 13:1 in an 06 will equal 12.5:1: PUMP gas safe.

PDR[/b]

how does that work?[/b]
the 06 has a shorter rod and a slightly larger combustion chamber


so what does a 12.5:1 hc piston come out to be ?[/b]
an 12.5:1 04 piston in an 06 will be around 12:1

what is the compression of a stock 06 piston?[/b]
11.4:1
 

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so in a 06 if you run a 13.5:1 hc piston it equals to 12.5:1? how does that work? so what does a 12.5:1 hc piston come out to be and what is the compression of a stock 06 piston?[/b]
if you read the post he is talking about puting a hc piston from a pre 06' in his 06'.........if the piston says its for an 06' then the compression it states (ex. 13.5:1) is what it actualy is
 

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if i get a 13.25:1 cp piston for my 2007 yfz450 will it go down to a 12:1? and pump gas safe
 
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