what compresion?

[kfx400rider03]

well im gonna be buying a cp or je piston soon. i just not to sure what compresion to get. i dont want to run race but if there is a compresion that i could run a octane booster? i would run half and half on race gas to pump gas if i have to. but im not sure if that is safe to do. any input would be helpful
thanks

[leasureryan]

12.5:1 is the highest I would recommend. any higher and you need race fuel. pretty high comp stock

[kfx400rider03]

when im looking up je im only finding 12;8.1 for the lowest compresion on a stock bore. and how come the je pistons are about $50 cheap than cp on some websites? are cp that much better?

[atveric132]

call mike at atp and get there 12:5:1 you can run pump gas and there custom JE piston uses stock rings so its not as hard on the cylinder

[kfx400rider03]

i just went on there websie and saw that they have them but they are realy exspenive. $249 for the 12;5.1. i went on burgards website and they have a 12:1 piston for $185.
why is atp's so much more??? after i buy gaskeys it will be $300 for a piston:huh. and how much of a difrence in the 2 difrent piston is there going to be? cant be much can it?

[Stiles86]

i paid about 190 for a 13.5 je keep on looking good deals are out there... never had issues with je im not sure what the limits are for pump gas thoe

[monkeybutt914]

magic racing has the 12:8 on sale right now for $169.95

[kfx400rider03]

but 12;8.1 i have to run race gas right? and i saw a couple deals on the 12;8.1

would i have to run race gace with 12.1? found one on burgard.com

[honda250xman]

ebay man, you can get pretty much any size compression for around 160 shipped. i would think that 12:8:1 would be ok on pump gas but i wouldnt risk the motor. and octane booster isnt really recommended but it can be done

[monkeybutt914]

hey i found this in an article on thumper talk... it might help with ur decision.
http://www.thumpertalk.com/forum/showthread.php?t=716908

Race gas is a generic term that refers to various fuels available, but it always comes up when discussing compression ratios. The question you should ask regarding race gas is “Do I need to run high-octane fuel with my high-compression piston?” High-compression engines can lead to pre-ignition or detonation if run too lean on the jetting or when using too low of a fuel octane rating (like 87 or 89 Pump Octane Number). Commonly available high-compression pistons, such as a 12.5:1 or 13.5:1 piston, run fine on pump 93-octane fuel when jetted properly. The problem is oftentimes, riders/engine-builders make other modifications to an engine in conjunction with a high-compression piston, such as race cams or a pipe. Subsequently, the combination of all the high-performance modifications can make the engine too high strung for pump 93-octane fuel. However, if you simply replace a stock compression piston with a 12:5 or 13.5:1 high-compression piston, they run very well on pump 93-octane fuel.