Most mod work for added speed will come from the crank... Sleeve porting will help some ie. raising the exhaust port a tad bit to increase the exhaust exit flow. You must also match the block's exhaust port height to the sleeve... I've mod my EVO II and the motor now is a monster... If you've never mod'd a motor, don't try it unless you have a test motor you can play with... As far as the Crank, this is where the most speed boost comes from... There are a few things you can do to your Sirio to make it into a Super motor... Advancing the timing on the crank, smoothing rough or sharp edges around the exit of the center port, Mod's to the induction port is key as well and must be done with great care... Murnan does some great work on Sirio's and at a very fair price... You can spend $300.00 plus dollars for a Sirio WC12 or Collari... or you can buy a EVO II at almost have the price mod it you're self. Remember, Murnan does great work on Sirio's if you want your motor done by a pro...
http://murnanmodified.360k.com/index.html Also, it'll take almost a half gallon of fuel to completely break in a Sirio, so the power will get better as motor becomes completly broken in. I want to see a modded Collari as well... Not just the sleeve but the crank as well... From ever angle possible...
RC_Alan