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- Thread starter I AM B17
- Start date

66 * 66 * 3.1415 = 13684.374.....add 900mm*2 = 14584.374..... divide by 3.1415 = 4642.487, take the square root = 68.136mm

68.136mm is the max allowed bore, Stock bore is 66mm.

http://www.mk5cortinaestate.co.uk/calculator2.php

66 * 66 * 3.1415 = 13684.374.....add 900mm*2 = 14584.374..... divide by 3.1415 = 4642.487, take the square root = 68.136mm

68.136mm is the max allowed bore, Stock bore is 66mm.

Dont mean to nit pick Ted, but 68mm bore will yield a 261cc capacity. Also most 250's after 2001 are 66.4 stock bore and 72 stroke.

http://www.mk5cortinaestate.co.uk/calculator2.php

Actually Tim, thats a really good point to argue. I hope you also argue the case of 450mx competing with the 250mx 2 strokes in AMA. Also that the 125's couldnt even get a look in until they allowed the 144cc conversion.

66 * 66 * 3.1415 = 13684.374.....add 900mm*2 = 14584.374..... divide by 3.1415 = 4642.487, take the square root = 68.136mm

68.136mm is the max allowed bore, Stock bore is 66mm.

Ted,

If I'm not mistaken on my math, 67.2mm bore will get you to 255cc. ------

r^2 x pi = square mm of bore cross-section

square mm of x-section x 255 / 246 gets the desired (max) square mm x-section for 255cc

s-mm-x-section / pi , then take the square root and multiply by 2 to get the bore size for 255cc

Should be about 67.2mm

PM

Just the aggravation of sending out to be replated lolThis whole thread is irrelevant now, at the time 250cc was the max under UAS. Now it's 300cc.

And, the TRX cylinders were steel bore cylinders. Most use the CR250 style cylinders, which are Nikasil plated. Which negates needing to bore them when rebuilding.