Honda trx 250 r over-bores

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.

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.
 
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

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.
 
Long stroke and 68.5mm bore
 

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This 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.
 
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.

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
 
This 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.
Just the aggravation of sending out to be replated lol
 
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