say i have my lt250r bored out .8 over with a wiseco would that change my displacement ??? if so how much ?? would it be like a 260 or sumthin

 

Yes it would, thats a 69mm piston which would make it a 261.73 cc cylinder.

 

How do you calculate the displacement 400fnsport ? I have a LT500R bored 120,000 over with an 89mm wiseco piston.

 

(bore in cm's)*(bore in cm's)*(stroke in cm's)*(0.0007854)= displacement in cc's

stock zilla: (86)*(86)*(86)*(0.0007854)= 499.56 cc's

120 over (not 120,000 over!): (89)*(89)*(86)*(0.0007854)= 535.02 cc's

140 over (max for LT500 with stock sleeve): (89.5)*(89.5)*(86)*(0.0007854)= 541.05 cc's

 

Triple knows what he is talking about[img]i/expressions/face-icon-small-happy.gif[/img]

 

Thanks guys.

 

hey triple, i have a quick question about a honda pro-x 310 kit if you don't mind.
i had it bored and a new piston sent to me. after installing it. i noticed the piston was about 1/4 inch from the top of the cylinder. compression is at 85 psi. i have a cylinder spacer on it. any chance they sent me the wrong piston. piston is a 72.20 mm
i'm thinking about removing the spacer and recheck the compression. thanks, airtime

 

That is definitely the wrong piston for your kit. The diameter of the piston isn't the only factor to consider. You also need to have the correct piston-pin-to-piston-top distance. If you look at your old piston, and compare it to the new one, you will notice a difference in that relationship. I would suggest ordering your parts from the original engine builder since different builders use different combinations of parts to form their kit. Aspects that matter are whether or not any or all of the following have been done: is the crank stroked; has the length of the connecting rod been changed; has a base spacer been added; and (as appears to be your situation) has a piston with different critical dimensions been utilized (perhaps by using a piston originally designed for a different application like a dirt bike).