YZ125 Stroker motor

I have always felt that going to 144 with just a bore would make it rev slow and the top end power would suffer. Been thinking about building with a bore and stroke to achieve a 144 or 151. Anybody here ridden one? Compared it to a full mod 125 or 144 big bore?

well,.......nobody building any strokers. Is it because they don't out perform or just cause they are so expensive?

I have always felt that going to 144 with just a bore would make it rev slow and the top end power would suffer. Been thinking about building with a bore and stroke to achieve a 144 or 151. Anybody here ridden one? Compared it to a full mod 125 or 144 big bore?

There is no comparison, the 164cc, 151cc, and 144cc out performs the 125 hands down.

If you need any other info please ask.

Gene

HI-TECH HORSEPOWER

I just picked up a YZ125.

I'm 130lbs ready to ride.

If I left my bore at 125, what would a stroker kit do for me.

What options are out there & what mods are needed.

I can only assume that the overbore market is strong because their gains are higher or cheaper than stroking.

I just picked up a YZ125.

I'm 130lbs ready to ride.

If I left my bore at 125, what would a stroker kit do for me.

What options are out there & what mods are needed.

I can only assume that the overbore market is strong because their gains are higher or cheaper than stroking.

There is more to deal with when over boring a cylinder to make the most out of the performance, if port timing isn't correct you can lose performance.

+4MM Stroker

balance crank

machine cases

re port cylinder

head mod

timming mod

Gene

If you need any more detail PM me.

I guess my question is more "How does a 144 big bore compare to a 144 acheived by a +2 bore and +4 stroke?"

Not really whats makes the most power but...the character of the powerband?

i think he want to know if it is better to gain the extra cc by stroking or boring. in my eyes i think that both setup would perform good(i cant tell you which is best). but i can tell you that for one of these motors to perform best it will take a lot more than just a crank or a bigger piston, there are numerous varibles, port time, crank case volume, port lengths. when yamaha builds a bike al these factors come into play. that is why i would love to see yamaha make a 167 or something like that because the entire motor and tranny would be made for it, thats i why i think the ktm 144 is so successful. i wish i could tell you more but just make sure you find some one good to build it and dont be scared to dump the extra money into everything else besides the intial bore or stroke, because those are what really make the most out of you bore or stroke

I guess my question is more "How does a 144 big bore compare to a 144 acheived by a +2 bore and +4 stroke?"

Not really whats makes the most power but...the character of the powerband?

Go with the +2 bore(56mm)/+4 stroke instead of the Big bore 144cc 58mm piston--For design/performance reasons.

The 56mm piston works better with the port designs and porting on the 125's than the 58mm piston. For exsample thats wy KTM changed there 144cc motor design(bore/stroke), they dont use a 58mm piston because of the port design on the 125.

You'll get a wider torque spread(bottom to top) with the 56mm bore/58.5

stroke.

Gene

Go with the +2 bore(56mm)/+4 stroke instead of the Big bore 144cc 58mm piston--For design/performance reasons.

The 56mm piston works better with the port designs and porting on the 125's than the 58mm piston. For exsample thats wy KTM changed there 144cc motor design(bore/stroke), they dont use a 58mm piston because of the port design on the 125.

You'll get a wider torque spread(bottom to top) with the 56mm bore/58.5

stroke.

Gene

Thanks Gene, That's what I'm looking for!!:thumbsup:

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