Building a YZ144 to run against a 150SX

My research has shown me that the best way to build a YZ144 is to change the stroke and bore. There is currently a kit on ebay. I'm just wondering if anybody has some feedback that has done it. The new KTM 150SX is a very impressive machine, especially with the new linkage suspension. The Athena big bore kit only produces only a modest power increase that is insufficient against the KTM. I'm curious if it can be done.

If it was my money I'd be sending it to Eric Gorr (Forward Motion). He will modify your current cylinder or you could try to find an extra on ebay. He will port the cylinder based on your preferences before having the cylinder replated. A YZ144 requires no change to the stroke, only the bore is increased.

Check out this site for lots of good info:

If you want a 150sx eater you need to build a 167, I beleive both Eric and max rpm both build them. It's not cheap but the gains are impressive and they stroke it like you mentioned wanting.

There is no need to stroke it - just good port work will get you there.

The 150 will have slightly better low end - but beyond that the 144 can be amazing when done well.

To each his own dyno depending, some here will get this concept, some wont - but the yz144 kit when developed fully will put out approximatively 25 percent more power than a stock yz125. If you measure 33 on your dyno for a stocker - you can get 41+ from a 144 with more power everywhere.

On that same "scale" the ktm 150 is around 38 peak.

The "lowest" reading on that graph is a relatively highly modified yz125. A stocker on this graph puts out about 23.

The highest reading is a new 11 RMZ450 with 10 hours on it.

The Red is a full mod 10 honda 250f.

The brown is a stockish honda 250f with good race fuel and mapping to suit

The blue is a full blown yz144, all bore no stroke.


Hope this sheds some light on your questions - on this scale a 150sx puts down about 27 in stock form (impressive no doubt for a stock bike).

I agree with Derek here, in the land of OZ where they run the 150cc School buy class the Aussie YRD YZ 144 have been beeting the KTM 150s on the track.

Obviously ride imput is required but 1 & 2nd in the national championship is impressive.

Mine rips

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