Stock displacement is 246cc, max allowed is 255, so you're allowed to gain 9cc's in area, so working in reverse...
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.
Yeah Stock bore and stroke on the honda 250's are 72mm stroke and 66mm bore, how ever running a displacement calculator I found that a 67mm piston would put you at 253cc and the next size over bore would put you at 257cc which is illegal in UAS racing. I think this alone is a good reason to change the displacement rules regarding the 250cc 2 strokes. only being able to rebore a couple piston sizes isn't realistic. and at the 68mm piston you'd be 261cc still some 40cc less than a wankle.
http://www.mk5cortinaestate.co.uk/calculator2.php
Stock displacement is 246cc, max allowed is 255, so you're allowed to gain 9cc's in area, so working in reverse...
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.
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.