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How do i understand port timing numbers?

idiotwithasaw

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Ok say I have degreed my saw, now what. What do my numbers tell me, I don't come from a mechanical engineering background, this is just a hobby for me. Feel free to talk down to me like I'm a little slow and explain. What numbers are ideal? What makes them ideal? I understand not every saw is the same and a lot of factors change things, like port shapes,etc. Right now I'm just looking for general information like you would get if we were in school.

I have a lot of questions and I hope others feel free to come here and ask as well. I want to make this site a place where we can come to learn.
 

Danders

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A degree wheel is just going to give you the ability to know when the exhaust, transfers and intake are opening and closing. If your exhaust is opening 100 deg after top dead center, it also has to be closing 100 degrees before top dead center. With 360 degrees in a circle, we can calculate how long, in crank degrees, a given port is going to be open based on the opening and closing points. 160 degrees in the example exhaust port. This tells you duration but nothing about flow.

You're right that saws are different so there isn't a single magic set of numbers that works on every saw. I don't have a lot of practical experience with this, I've only done three saws. I've relied heavily on other folks advice around port timing.
 
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