How do you figure out your Exhaust Blow down duration

[crawl9]

Is their a formula to figure what blowdown duration on a 2-stroke. I have the degrees when the exhaust opens and the port opens and the port sizes.
thanks

 

[Jman271]

The blown down is the time when your exh opens until the transfers open. If you have a degree wheel, you could chart it in deg. I just did my 03 125sx, the exh opened @ 81 deg from tdc, then the main transfers opened @ 112deg, which gave me 31 deg of blown down. The rear transfers were staggered by a few deg, they opened @ 115 deg. Not sure if that counts towards the blow down, since they are secondary, but I figured I would throw that in there. Also how wide they are would make a diff too. As far as what the perfect time is, that is the million $$$ question, b/c the key to 2 making power in a 2 stroke relys on the blow down. Hope that was what you were looking for.