Inexpensive Performance Modifications
for Yamaha Thumpers
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 bit’s the head, it’s a fine line between success
and total failure so we spend a bit of time carefully porting and flow
testing to ensure it doesn’t become scrap metal.
The flow result indicates that we’ve 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 it’s 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 it’s 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
Article on WR450 Engine Rebuild
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* Prices are subject to change without notice |
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