2mm stroker

[CR480R]

If an engines stroke was increased 2mm without corrective porting would there be any performance gains? Any losses? Would it affect port timing much?

[Kane]

I can't see much for loss but the only real gain would be through the added compression and a bit more torque from the added stroke as well. Those gains would really be modest without the porting to take advantage of the added stroke. As well you want to do a head check to insure the piston crown clearance if you do the stroke.

[CR480R]

The reason I ask is I am in need of a crank for my '91 kdx250 bottom end... I think the more plentiful '92 and newer KX cranks will physically interchange but they have 2mm additional stroke... Would it be better to make a cylinder spacer? or step-cut the head for the proper squish clearance?

[flotek]

Originally Posted by cr480r

If an engines stroke was increased 2mm without corrective porting would there be any performance gains? Any losses? Would it affect port timing much?

you could do either , if it was me id drop the ports and use a 1mm spacer or gasket with same head. it would gain some noticable lowend torque just be sure your squish clearance is okay and the cases wont require any trenching .and obviously be sure everything is interchangable too

[CR480R]

Originally Posted by eviltwin

you could do either , if it was me id drop the ports and use a 1mm spacer or gasket with same head. it would gain some noticable lowend torque just be sure your squish clearance is okay and the cases wont require any trenching .and obviously be sure everything is interchangable too

Thanks Evil.. I am going to try it... I have to split the case either way and ebay is flooded with these cranks... if it dont work... not much $$ wasted... If it doesnt run good I will just have it ported to match...