Exhaust theory

[Thesandman]

On my çs4910 I measured the ex port, muffler flange, muffler exit hole and exit hole cover. All in square inches@ .43, .68, .38 and cover @.3. after opening it up alot. What am I looking for? No restrictions? I expect to make ex port much larger eventually but for now what is common practice?

 

[Ketchup]

Not sure for 4910, but the ballpark for ported saws is 80-100% of exhaust port area at the muffler outlet. No restrictions in between. Infinite ways to skin that cat though.

 

[Funky sawman]

I do 120 percent larger on the outlet port, because I take into account the restriction that a usfs approved spark screen makes. Never had issues with power loss or idle issues, but much bigger will cause issues. I talking about stock saws here

 

[Ketchup]

I do 120 percent larger on the outlet port, because I take into account the restriction that a usfs approved spark screen makes. Never had issues with power loss or idle issues, but much bigger will cause issues. I talking about stock saws here

Good point. Screens restrict the outlet a lot. 120% with a screen has worked really well on several of my saws. And they help with noise.

Also, multiple ports won’t flow as much as a single port of the same total size.

 

[Woodwater]

the more beans you eat, the bigger the exhaust should be.

 

[huskihl]

Factory screen flows about 30% I believe. You’ll notice there is always some distance between the oem exit hole and the screen. So if using the factory screen, there’s not much to be had from opening the hole much more than 1/3 the size of the screen