WR/YZF250 Hotup

Inexpensive Performance Modifications for Yamaha Thumpers
YZF250 Dyno Graph
YZF250 Dyno Graph

What a fun job this is, and even more fun to ride. The YZ250 we had was all stock and put out about 28hp with a slip on muffler. 
Head and barrel off and stock piston out, (it makes a good  ash tray). 

Wiseco make a good light high compression piston which comes with rings and piston pin, give the bore a very light hone and carefully fit the piston in the barrel, easier said than done.

The tricky bitís the head, itís a fine line between success and total failure so we spend a bit of time carefully porting and flow testing to ensure it doesnít become scrap metal.

The flow result indicates that weíve done a good job and on it goes, after some modifying to the gasket and checking that valve to piston clearance is acceptable we do the final assembly. Once every thing is dialed in itís back on the dyno for a final tune and look at that 35hp, that's about 30% increase.

Danny Bray has been racing this all year and not had any engine failures  so itís also reliable as well as fast. 
Check out the graphs for yourself.
 

What it costs*:

  • Wiseco piston kit $190.00
  • Port and flow head $350.00
  • Gaskets $150.00
  • Strip and assemble $295.00
  • Dyno and tune $195
YZ250F on Dynojet Dyno
YZ250F on the dyno
Superflow 110 Flowbench.jpg
Flowbench

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