Kennedy just told you, put a degree wheel on the end of the crank and when the exhaust starts to open see what the wheel is, you can put it at zero then continue turning the engine over until the transfer ports open and read the wheel again that will tell you your blowdown time, if you don't understand how to set up a degree wheel or own one then dont bother trying to figure it out, and like they already said 28 isn't what you want and if you don't have porting tools to correct this, then send your cylinder to the guys that understand it and have the tools