torque

[Roma]

I own a 2001 YZ-250F. The bike does have a PC pipe and header and 2 teeth larger on the rear sproket. I rode an 04 YZ-250F with the exaxt same mods and while I loved how light the 04 felt I could not help notice how much more torque and low end my bike has. What did they change in 04 to make it so 2 stroke like? If I buy an 04 can I make it like mine by adding more flywheel or changing cams? I race mx but like the torque of the 01. This is my first post.

 

[stangale]

You're right.
(I have an 01 and an 04.)
It's too early for the aftermarket to offer us more low/mid grunt to go with the wonderful top end.
In the meantime, use the clutch like a 2-stroke when you have to, and maintain more corner speed so you don't have to use it (I know - easier said than done.)
Best,
Stan Gale
Los Angeles

 

[Rich Rohrich]

You could use the Falicon adjustable cam sprockets to shift the power around with the stock cams but it will take some work tuning it for the characteristics you want.

Probably the easiest and least expensive way to gain some significant torque at lower rpm is to use a properly designed megaphone exhaust system like the Thunder Alley system. Pipes can work wonders if they are designed properly, but most of the pipes that are being sold for these bikes are too short and too big to increase torque or provide any usefull increases in performance.

A 2mm big bore has an even greater influence on low & midrange torque but it will drop the peak torque rpm by about 600 rpm and isn't legal if you ride races that enforce to the AMA rulebook.

A big bore and a megaphone pipe makes a huge change in the torque available from these engines without giving up the good characteristics it already has.

There are lots of good affordable options already available for these engines, it just takes looking beyond the pages of the popular magazines for the answers. :thumb: