250x .40 over bore???

[rap169]

I have an 87 250x . I want to bore the cylinder .40 over. The stock ccs are 246.4 . What will the cc's be after the bore? Is there a calculation for this. i know that the piston is 74mm and stoke of 57.3 Its gonna be a wiesco piston. anybody have this size bore? and what kind of gain did u notice from it? would i have to rejet for this? thanks in advance.

[wheeltrax]

I dont know what the calculation is going to be after that. but you dont really notice that much of a gain. The different piston will make a difference over stock because its lighter for one and there made better. But its not going to be anything bar ripping in terms of power increase.

[spliffy]

I'm Not Sure On the cc's But I Do Know That You Won't Barely See Any Power Increase In It... As Long As You Have It That Torn Apart It Would Be Worth Your While To Go .080 Over (Doesnt Cost Any More) & Throw A Cam In It... I Suggest The Web Drop In Cam.. You Don't Need Hardened Rockers With That One , You Will Have To Rejet To Get The Ultimate Perf Out Of It , But You Will Notice A Good Amount Of Power Increase From A Stock Cam & Bore... Also Throw A K&N On It After That. :macho

[outlaw319]

here ya go!!!!
bore x bore x stroke x .0007854=cc's
for every .020 over = .5 mm stock 250 bore is 74mm .040=75mm
stock 250X
74 x 74 x 57.3 x .0007854= 246.43872 (246cc)
250x bored .040
75 x 75 x 57.3 x .0007854= 253.14423 (253cc)
Hope this helps!

[rap169]

yes that calculation is what i was hoping for. Thanks. I already have a k&N. full RCM Race pipe, and jet work. But i dont want to take my cylinder to the limit. I want to leave room if i need to put new rings in the future for larger bore. I plan on a cam too whiles its apart, and possible head work. Is the web cam a race cam, or all around. I plan on mx race once in a while, and trail riding now and then, i want something good, but nothing tooo radical that i cant drive it on the trail. Thanks

[outlaw319]

Webcams sell both a race cam and all around cam! I would go with an "all around" cam since you're not wanting something to radical. If you get a full "race cam, then you'll need a set of valve springs to go with! More $$$$! Some headwork (porting) will definitly help out the restrictive head on your quad! If you want to race some MX I would suggest some suspension mods more than engine:D .

[rap169]

already got the suspension....400ex a-arms and shocks, raptor rear shock.

[outlaw319]

does the Raptor rear make a big difference? does it bolt right on, or do you have to modify?
I'm currently installing an 350 swing arm and rear shock on mine, and my old 250R LSR standard length A-arms and "R" works shocks!

[rap169]

it bolted right on....i love it. I broke my original one on the top mount, it snapped right off, and was leaking badly. The raptor shock made a huge difference. I left the raptor spring on it and i weigh 165. I dont think its too stiff either. This was a cheap alternative to buying a aftermarket shock. And i didnt have the money to spend at the time....so i my opionion it was a great investment.