More Top End

[Mxer4lyf]

Hey i currently own a 2003 YZ250 and i was wondering how can i get more top end power. I currently have boyesen carbon fiber reeds and a pro circuit works pipe.

[canufeelme]

only thing i can think of is put a bigger piston in it.

[Yamaha_Freak]

porting....

[Mxer4lyf]

well i was thinkin about porting but would adding a new reed cage be the same (almost the same amont of power gain but cheaper)?

[ONLY2STROKES]

no...porting a 2stroke will give you the biggest gains..much much more than a reed valve.

[Mxer4lyf]

k
and wat about a silencer does the shorty kill lots of top end?

[ONLY2STROKES]

shorty's usually give a greater increse on top..make sure to repack it often.

[Mxer4lyf]

i thought shorty was for low end
but i heard that it dont kill the top

[ONLY2STROKES]

well the length and diameter of the core both are related to the power curve...from what i have gathered over some time is this...smaller diameter core and longer silencer=bottom end...larger diameter core and shorter=more up top...i know some guys that drag/hill race..will cut off inch by inch, till they get the best timeslip....silencers are real important and they must be designed to work with the pipe...

[nd4speed]

Tuning for Specific Powerbands


Component: Cylinder Head

Low To Midrange: 9.5:1 compression ratio, squish band 60% of bore area

Midrange and High-Rpm: 8:1 compression ratio, 40% squish

Component: Cylinder Ports

Low To Midrange: Exhaust port 90 ATDC, transfer ports 118 ATDC

Midrange and High-Rpm: Exhaust port 84 ATDC, transfer ports 116 ATDC

Component: Reeds

Low To Midrange: Dual-stage or .4mm fiberglass petals.

Compromise: Thick carbon fiber petals

Midrange and High-Rpm: Large area 30-degree valve

Component: Carburetor

Low To Midrange: Smaller diameter or sleeved down carb (26mm for 80cc, 34mm for 125cc, 36mm 250cc)

Midrange and High-Rpm: Larger carb (28mm for 80cc, 38mm for 125cc, 39.5mm 250cc)

Component: Pipe

Low To Midrange: Fatty or Torque

Midrange and High-Rpm: Desert or Rpm

Component: Silencer or Spark arrestor

Low To Midrange: Short, small diameter

Midrange and High-Rpm: Long, large diameter

Component: Ignition Timing Advance timing

Low To Midrange: Stock timing

Midrange and High-Rpm: Retard timing

Component: Flywheel

Low To Midrange: Add weight

Compromise: Stock flywheel

Midrange and High-Rpm: PVL internal flywheel

Component: Fuel

Low To Midrange: Super unleaded 93 octane

Midrange and High-Rpm: Racing fuel 105 octane