what is the cc's of a stock rod stock crank lt250r when bored 40 and 60 over? What is the formula for figuring this out?

 

I don't know the formula but I do know what mm they are 68mm(.040) and 68.50mm(.060). Hope this helps, if not I'm sorry

 

What is the stroke?

 

70mm

 

Does this make sense?

67mm x 70mm somehow equals the original displacement of 246 cc's. 67 x 70=4,690 divided by 246 19.06ish


68.5 x 70 = 4,795 divided by 19.06 = 251.57ish.... Would 68.5mm x 70mm would be around 252 cc's....

Close?

 

Hey,

i think this is right . . . the formula for the volume of a cylinder is Pi*r^2*h (not sure how to say r squared on the computer). r = radius of the bore and h = length of the stroke.

so . . . if stock bore/stroke is 67mm X 70mm then the displacement (aka, volume of the cylinder) = (3.14) * (33.5 * 33.5) * 70 = 246670.55mm^3 to convert mm^3 to cc^3 you divide by 1000. thus giving you a stock displacement of 246cc. (^3 means a number cubed)

so . . . .040 over = a bore of 68mm then your new displacement = 254cc

and . . . .060 over = a bore of 68.5mm then displacement is now = 258cc

like i said, i think that's the right way to do it. if not, i'd enjoy knowing the correct way.

cheers,
bigmac

 

Bore x Bore x .7854 x Stroke =cc's

 

40 over would be 254cc and 60 over would be 256cc

 

Hey,

jmc - i'm not exactly sure why, but yea, your formula works, but you have to divide by 1000 at the end to get from mm's to cc's.

racerx81 - how did you do your math? i'm just curious about how your got your 60 over number? following my math or jmc's math, both give you 258cc's at 60 over. but maybe i did something wrong?

cheers,
bigmac

 

According to Vito's the formula is:bore divided by 2=A

AxAx3.14xstroke divided by 1000=cc's

EX: 86mm Divided by 2=A

AxAX3.14xthe stroke divided by 1000=cc's

Or just go to www.mcdizzy.com,this site has all kind's of formula's to look at.